diff --git a/.editorconfig b/.editorconfig
new file mode 100644
index 00000000000..bfe127253e2
--- /dev/null
+++ b/.editorconfig
@@ -0,0 +1,12 @@
+# See: https://editorconfig.org
+root = true
+
+[*]
+charset = utf-8
+
+[*.hs]
+indent_style = space
+indent_size = 2
+
+[Makefile]
+indent_style = tab
diff --git a/.github/mergify.yml b/.github/mergify.yml
index 46eae2f7a80..7f7712394dd 100644
--- a/.github/mergify.yml
+++ b/.github/mergify.yml
@@ -52,15 +52,7 @@ pull_request_rules:
         - label=merge+no rebase
       - '#approved-reviews-by>=2'
       - '#changes-requested-reviews-by=0'
-      # oy
-      # lifted these from branch protection imports
-      - check-success=fourmolu
-      - check-success=hlint
-      - check-success=Meta checks
-      - check-success=Doctest Cabal
-      - check-success=Validate post job
-      - check-success=Bootstrap post job
-      - 'check-success=docs/readthedocs.org:cabal'
+      - '#check-failure=0'
 
   # rebase+merge strategy
   - actions:
@@ -73,6 +65,7 @@ pull_request_rules:
       - label=merge delay passed
       - '#approved-reviews-by>=2'
       - '-label~=^blocked:'
+      - '#check-failure=0'
 
   # merge+squash strategy
   - actions:
@@ -85,6 +78,7 @@ pull_request_rules:
       - label=merge delay passed
       - '#approved-reviews-by>=2'
       - '-label~=^blocked:'
+      - '#check-failure=0'
 
   # merge+no rebase strategy
   - actions:
@@ -97,6 +91,11 @@ pull_request_rules:
       - label=merge delay passed
       - '#approved-reviews-by>=2'
       - '-label~=^blocked:'
+      - '#check-failure=0'
+      # unlike the others, we need to force this one to be up to date
+      # because it's intended for when Mergify doesn't have permission
+      # to rebase
+      - '#commits-behind=0'
 
   # merge strategy for release branches
   - actions:
@@ -109,6 +108,7 @@ pull_request_rules:
       - -body~=backport
       - '#approved-reviews-by>=2'
       - '-label~=^blocked:'
+      - '#check-failure=0'
 
   # merge+squash strategy for release branches
   - actions:
@@ -121,6 +121,7 @@ pull_request_rules:
       - -body~=backport
       - '#approved-reviews-by>=2'
       - '-label~=^blocked:'
+      - '#check-failure=0'
 
   # merge strategy for backports: require 1 approver instead of 2
   - actions:
@@ -133,6 +134,7 @@ pull_request_rules:
       - body~=backport
       - '#approved-reviews-by>=1'
       - '-label~=^blocked:'
+      - '#check-failure=0'
 
   # merge+squash strategy for backports: require 1 approver instead of 2
   - actions:
@@ -145,6 +147,7 @@ pull_request_rules:
       - body~=backport
       - '#approved-reviews-by>=1'
       - '-label~=^blocked:'
+      - '#check-failure=0'
 
   # backports should be labeled as such
   - actions:
diff --git a/.github/workflows/format.yml b/.github/workflows/format.yml
index d54310be613..116537cf2ea 100644
--- a/.github/workflows/format.yml
+++ b/.github/workflows/format.yml
@@ -17,3 +17,4 @@ jobs:
           Cabal/**/*.hs
           Cabal-syntax/**/*.hs
           cabal-install/**/*.hs
+          cabal-validate/**/*.hs
diff --git a/.github/workflows/validate.yml b/.github/workflows/validate.yml
index 947b47a5f12..23fe4e5e7d1 100644
--- a/.github/workflows/validate.yml
+++ b/.github/workflows/validate.yml
@@ -124,6 +124,11 @@ jobs:
           rm -rf ~/.config/cabal
           rm -rf ~/.cache/cabal
 
+      - name: "WIN: Setup TMP environment variable"
+        if: runner.os == 'Windows'
+        run: |
+           echo "TMP=${{ runner.temp }}" >> "$GITHUB_ENV"
+
       - uses: actions/checkout@v4
 
       # See https://github.com/haskell/cabal/blob/master/CONTRIBUTING.md#hackage-revisions
@@ -236,29 +241,24 @@ jobs:
           name: cabal-${{ runner.os }}-${{ env.CABAL_ARCH }}
           path: ${{ env.CABAL_EXEC_TAR }}
 
-      - name: Validate lib-tests
+      - name: Validate tests
         env:
           # `rawSystemStdInOut reports text decoding errors`
           # test does not find ghc without the full path in windows
           GHCPATH: ${{ steps.setup-haskell.outputs.ghc-exe }}
-        run: sh validate.sh $FLAGS -s lib-tests
-
-      - name: Validate lib-suite
-        run: sh validate.sh $FLAGS -s lib-suite
-
-      - name: Validate cli-tests
-        run: sh validate.sh $FLAGS -s cli-tests
-
-      - name: Validate cli-suite
-        run: sh validate.sh $FLAGS -s cli-suite
-
-      - name: Validate solver-benchmarks-tests
-        if: matrix.ghc == env.GHC_FOR_SOLVER_BENCHMARKS
-        run: sh validate.sh $FLAGS -s solver-benchmarks-tests
-
-      - name: Validate solver-benchmarks-run
-        if: matrix.ghc == env.GHC_FOR_SOLVER_BENCHMARKS
-        run: sh validate.sh $FLAGS -s solver-benchmarks-run
+        run: |
+          set +e
+          rc=0
+          tests="lib-tests lib-suite cli-tests cli-suite"
+          if [ "${{ matrix.ghc }}" = "${{ env.GHC_FOR_SOLVER_BENCHMARKS }}" ]; then
+            tests="$tests solver-benchmarks-tests solver-benchmarks-run"
+          fi
+          for test in $tests; do
+            echo Validate "$test"
+            sh validate.sh $FLAGS -s "$test" || rc=1
+            echo End "$test"
+          done
+          exit $rc
 
   validate-old-ghcs:
     name: Validate old ghcs ${{ matrix.extra-ghc }}
@@ -312,11 +312,13 @@ jobs:
           restore-keys: ${{ runner.os }}-${{ env.GHC_FOR_RELEASE }}-
 
       - name: Validate build
+        id: build
         run: sh validate.sh ${{ env.COMMON_FLAGS }} -s build
 
       - name: "Validate lib-suite-extras --extra-hc ghc-${{ matrix.extra-ghc }}"
         env:
           EXTRA_GHC: ghc-${{ matrix.extra-ghc }}
+        continue-on-error: true
         run: sh validate.sh ${{ env.COMMON_FLAGS }} --lib-only -s lib-suite-extras --extra-hc "${{ env.EXTRA_GHC }}"
 
   build-alpine:
@@ -399,7 +401,6 @@ jobs:
         # We need to build an array dynamically to inject the appropiate env var in a previous job,
         # see https://docs.github.com/en/actions/learn-github-actions/expressions#fromjson
         ghc: ${{ fromJSON (needs.validate.outputs.GHC_FOR_RELEASE) }}
-
     defaults:
       run:
         shell: ${{ matrix.sys.shell }}
@@ -416,12 +417,17 @@ jobs:
           esac
           echo "CABAL_ARCH=$arch" >> "$GITHUB_ENV"
 
-      - name: Work around XDG directories existence (haskell-actions/setup#62)
+      - name: "MAC: Work around XDG directories existence (haskell-actions/setup#62)"
         if: runner.os == 'macOS'
         run: |
           rm -rf ~/.config/cabal
           rm -rf ~/.cache/cabal
 
+      - name: "WIN: Setup TMP environment variable"
+        if: runner.os == 'Windows'
+        run: |
+           echo "TMP=${{ runner.temp }}" >> "$GITHUB_ENV"
+
       - uses: actions/checkout@v4
 
       - uses: haskell-actions/setup@v2
@@ -451,6 +457,8 @@ jobs:
     name: Create a GitHub prerelease with the binary artifacts
     runs-on: ubuntu-latest
     if: github.ref == 'refs/heads/master'
+    permissions:
+      contents: write
 
     # IMPORTANT! Any job added to the workflow should be added here too
     needs: [validate, validate-old-ghcs, build-alpine, dogfooding]
@@ -459,32 +467,15 @@ jobs:
       # for now this is hardcoded. is there a better way?
       - uses: actions/download-artifact@v4
         with:
-          name: cabal-Windows-x86_64
-
-      - uses: actions/download-artifact@v4
-        with:
-          name: cabal-Linux-x86_64
-
-      - uses: actions/download-artifact@v4
-        with:
-          name: cabal-Linux-static-x86_64
-
-      - uses: actions/download-artifact@v4
-        with:
-          name: cabal-macOS-aarch64
+          pattern: cabal-*
+          path: binaries
 
       - name: Create GitHub prerelease
-        uses: marvinpinto/action-automatic-releases@v1.2.1
+        uses: softprops/action-gh-release@v2
         with:
-          repo_token: ${{ secrets.GITHUB_TOKEN }}
-          automatic_release_tag: cabal-head
+          tag_name: cabal-head
           prerelease: true
-          title: cabal-head
-          files: |
-            cabal-head-Windows-x86_64.tar.gz
-            cabal-head-Linux-x86_64.tar.gz
-            cabal-head-Linux-static-x86_64.tar.gz
-            cabal-head-macOS-aarch64.tar.gz
+          files: binaries/cabal-*
 
   prerelease-lts:
     name: Create a GitHub LTS prerelease with the binary artifacts
@@ -498,39 +489,22 @@ jobs:
     steps:
     - uses: actions/download-artifact@v4
       with:
-        name: cabal-Windows-x86_64
-
-    - uses: actions/download-artifact@v4
-      with:
-        name: cabal-Linux-x86_64
-
-    - uses: actions/download-artifact@v4
-      with:
-        name: cabal-Linux-static-x86_64
-
-    - uses: actions/download-artifact@v4
-      with:
-        name: cabal-macOS-x86_64
+        pattern: cabal-*
+        path: binaries
 
     - run: |
         # bash-ism, but we forced bash above
         mv cabal-{,lts-}head-Windows-x86_64.tar.gz
         mv cabal-{,lts-}head-Linux-x86_64.tar.gz
         mv cabal-{,lts-}head-Linux-static-x86_64.tar.gz
-        mv cabal-{,lts-}head-macOS-x86_64.tar.gz
+        mv cabal-{,lts-}head-macOS-aarch64.tar.gz
 
     - name: Create GitHub prerelease
-      uses: marvinpinto/action-automatic-releases@v1.2.1
+      uses: softprops/action-gh-release@v2
       with:
-        repo_token: ${{ secrets.GITHUB_TOKEN }}
-        automatic_release_tag: cabal-lts-head
+        tag_name: cabal-lts-head
         prerelease: true
-        title: cabal-lts-head
-        files: |
-          cabal-lts-head-Windows-x86_64.tar.gz
-          cabal-lts-head-Linux-x86_64.tar.gz
-          cabal-lts-head-Linux-static-x86_64.tar.gz
-          cabal-lts-head-macOS-x86_64.tar.gz
+        files: binaries/cabal-*
 
   # We use this job as a summary of the workflow
   # It will fail if any of the previous jobs does
diff --git a/.github/workflows/whitespace.yml b/.github/workflows/whitespace.yml
index b6604798f1e..a6869a59e3f 100644
--- a/.github/workflows/whitespace.yml
+++ b/.github/workflows/whitespace.yml
@@ -7,10 +7,21 @@ on:
 
 jobs:
   whitespace:
+    defaults:
+      run:
+        shell: bash
     runs-on: ubuntu-latest
 
     steps:
+
     - uses: actions/checkout@v4
-    - uses: andreasabel/fix-whitespace-action@v1
-      with:
-        verbose:    true
+
+    - run: |
+        # no longer using the action because apparently we're supposed to use the Makefile here
+        wget -q https://github.com/agda/fix-whitespace/releases/download/v0.1/fix-whitespace-0.1-linux.binary
+        mkdir -p "$HOME/.local/bin"
+        mv fix-whitespace-0.1-linux.binary "$HOME/.local/bin/fix-whitespace"
+        chmod +x "$HOME/.local/bin/fix-whitespace"
+        echo "$HOME/.local/bin" >> $GITHUB_PATH
+
+    - run: make whitespace
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 9a06d1c8329..93835320bb2 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -196,7 +196,9 @@ the code base.
 
 We use automated whitespace convention checking. Violations can be fixed by
 running [fix-whitespace](https://hackage.haskell.org/package/fix-whitespace). If
-you push a fix of a whitespace violation, please do so in a _separate commit_.
+you push a fix of a whitespace violation, please do so in a _separate commit_. For convenience,
+`make whitespace` will show violations and `make fix-whitespace` will fix them, if the
+`fix-whitespace` utility is installed.
 
 ## Other Conventions
 
@@ -346,13 +348,37 @@ description: {
 }
 ```
 
+Changelogs may also be written in "markdown-frontmatter" format. This is useful if your
+description contains braces, which must be escaped with backslashes in `.cabal` file
+format. The front matter is in YAML syntax, not `.cabal` file syntax, and the file
+_must_ begin with a line containing only hyphens.
+
+```markdown
+---
+synopsis: Add feature xyz
+packages: [cabal-install]
+prs: 0000
+issues: [0000, 0000]
+significance: significant
+---
+
+- Detail number 1
+- Detail number 2
+
+```
+The package list must be enclosed in square brackets and comma-separated, but this
+isn't needed for `prs` or `issues`; those are free-form and any YAML syntax will
+be accepted. Note that the number signs on PR and issue numbers are required in
+`.cabal` file syntax, but won't work in markdown-frontmatter syntax because they
+signify comments in YAML.
+
 Only the `synopsis` and `prs` fields are required, but you should also set the others where applicable.
 
 | Field          | Description                                                                                                        |
 | -----          | -----------                                                                                                        |
 | `synopsis`     | Brief description of the change. Often just the pr title.                                                          |
 | `description`  | Longer description, with a list of sub-changes. Not needed for small/atomic changes.                               |
-| `packages`     | Packages affected by the change (`cabal-install`, `Cabal`...). Omit if it's an overarching or non-package change.  |
+| `packages`     | Packages affected by the change (`cabal-install`, `Cabal`...). Omit if it's a non-package change.                  |
 | `prs`          | Space-separated hash-prefixed pull request numbers containing the change (usually just one).                       |
 | `issues`       | Space-separated hash-prefixed issue numbers that the change fixes/closes/affects.                                  |
 | `significance` | Set to `significant` if the change is significant, that is if it warrants being put near the top of the changelog. |
@@ -377,7 +403,7 @@ There are a few main venues of communication:
 
 * Many developers idle on `#hackage` on [`irc.libera.chat`](https://libera.chat). The `#ghc` channel is also a decently good bet.
   * You can join the channel using a web client, even anonymously: https://web.libera.chat/#hackage
-  * Alternatively you can join it using [matrix](https://matrix.org/): https://matrix.to/#/#hackage:libera.chat
+  * Alternatively you can join it using [matrix](https://matrix.org/): https://matrix.to/#/#hackage:matrix.org
 
 ## Releases
 
diff --git a/Cabal-syntax/Cabal-syntax.cabal b/Cabal-syntax/Cabal-syntax.cabal
index 0893f4f2588..42fb7f7d51e 100644
--- a/Cabal-syntax/Cabal-syntax.cabal
+++ b/Cabal-syntax/Cabal-syntax.cabal
@@ -135,6 +135,7 @@ library
     Distribution.Types.ConfVar
     Distribution.Types.Dependency
     Distribution.Types.DependencyMap
+    Distribution.Types.DependencySatisfaction
     Distribution.Types.ExeDependency
     Distribution.Types.Executable
     Distribution.Types.Executable.Lens
@@ -158,6 +159,8 @@ library
     Distribution.Types.Library.Lens
     Distribution.Types.LibraryName
     Distribution.Types.LibraryVisibility
+    Distribution.Types.MissingDependency
+    Distribution.Types.MissingDependencyReason
     Distribution.Types.Mixin
     Distribution.Types.Module
     Distribution.Types.ModuleReexport
diff --git a/Cabal-syntax/src/Distribution/Compat/Binary.hs b/Cabal-syntax/src/Distribution/Compat/Binary.hs
index 8849fc13b10..4927ec1e69b 100644
--- a/Cabal-syntax/src/Distribution/Compat/Binary.hs
+++ b/Cabal-syntax/src/Distribution/Compat/Binary.hs
@@ -20,4 +20,4 @@ decodeOrFailIO :: Binary a => ByteString -> IO (Either String a)
 decodeOrFailIO bs =
   catch (evaluate (decode bs) >>= return . Right) handler
   where
-    handler (ErrorCallWithLocation str _) = return $ Left str
+    handler (ErrorCall str) = return $ Left str
diff --git a/Cabal-syntax/src/Distribution/Compat/NonEmptySet.hs b/Cabal-syntax/src/Distribution/Compat/NonEmptySet.hs
index 17e3811e9a4..9e227459e84 100644
--- a/Cabal-syntax/src/Distribution/Compat/NonEmptySet.hs
+++ b/Cabal-syntax/src/Distribution/Compat/NonEmptySet.hs
@@ -12,6 +12,7 @@ module Distribution.Compat.NonEmptySet
 
     -- * Deletion
   , delete
+  , filter
 
     -- * Conversions
   , toNonEmpty
@@ -116,6 +117,9 @@ delete x (NES xs)
   where
     res = Set.delete x xs
 
+filter :: (a -> Bool) -> NonEmptySet a -> Set.Set a
+filter predicate (NES set) = Set.filter predicate set
+
 -------------------------------------------------------------------------------
 -- Conversions
 -------------------------------------------------------------------------------
diff --git a/Cabal-syntax/src/Distribution/PackageDescription/Configuration.hs b/Cabal-syntax/src/Distribution/PackageDescription/Configuration.hs
index e811c361221..eebf760094d 100644
--- a/Cabal-syntax/src/Distribution/PackageDescription/Configuration.hs
+++ b/Cabal-syntax/src/Distribution/PackageDescription/Configuration.hs
@@ -56,12 +56,13 @@ import Distribution.System
 import Distribution.Types.Component
 import Distribution.Types.ComponentRequestedSpec
 import Distribution.Types.DependencyMap
+import Distribution.Types.DependencySatisfaction (DependencySatisfaction (..))
+import Distribution.Types.MissingDependency (MissingDependency (..))
 import Distribution.Types.PackageVersionConstraint
 import Distribution.Utils.Generic
 import Distribution.Utils.Path (sameDirectory)
 import Distribution.Version
 
-import qualified Data.Map.Lazy as Map
 import Data.Tree (Tree (Node))
 
 ------------------------------------------------------------------------------
@@ -144,15 +145,17 @@ parseCondition = condOr
 
 ------------------------------------------------------------------------------
 
--- | Result of dependency test. Isomorphic to @Maybe d@ but renamed for
+-- | Result of dependency test. Isomorphic to @Maybe@ but renamed for
 --   clarity.
-data DepTestRslt d = DepOk | MissingDeps d
+data DepTestRslt
+  = DepOk
+  | MissingDeps [MissingDependency]
 
-instance Semigroup d => Monoid (DepTestRslt d) where
+instance Monoid DepTestRslt where
   mempty = DepOk
   mappend = (<>)
 
-instance Semigroup d => Semigroup (DepTestRslt d) where
+instance Semigroup DepTestRslt where
   DepOk <> x = x
   x <> DepOk = x
   (MissingDeps d) <> (MissingDeps d') = MissingDeps (d <> d')
@@ -190,13 +193,13 @@ resolveWithFlags
   -> [PackageVersionConstraint]
   -- ^ Additional constraints
   -> [CondTree ConfVar [Dependency] PDTagged]
-  -> ([Dependency] -> DepTestRslt [Dependency])
+  -> ([Dependency] -> DepTestRslt)
   -- ^ Dependency test function.
-  -> Either [Dependency] (TargetSet PDTagged, FlagAssignment)
+  -> Either [MissingDependency] (TargetSet PDTagged, FlagAssignment)
   -- ^ Either the missing dependencies (error case), or a pair of
   -- (set of build targets with dependencies, chosen flag assignments)
 resolveWithFlags dom enabled os arch impl constrs trees checkDeps =
-  either (Left . fromDepMapUnion) Right $ explore (build mempty dom)
+  explore (build mempty dom)
   where
     -- simplify trees by (partially) evaluating all conditions and converting
     -- dependencies to dependency maps.
@@ -216,7 +219,7 @@ resolveWithFlags dom enabled os arch impl constrs trees checkDeps =
     -- computation overhead in the successful case.
     explore
       :: Tree FlagAssignment
-      -> Either DepMapUnion (TargetSet PDTagged, FlagAssignment)
+      -> Either [MissingDependency] (TargetSet PDTagged, FlagAssignment)
     explore (Node flags ts) =
       let targetSet =
             TargetSet $
@@ -229,7 +232,7 @@ resolveWithFlags dom enabled os arch impl constrs trees checkDeps =
             DepOk
               | null ts -> Right (targetSet, flags)
               | otherwise -> tryAll $ map explore ts
-            MissingDeps mds -> Left (toDepMapUnion mds)
+            MissingDeps mds -> Left mds
 
     -- Builds a tree of all possible flag assignments.  Internal nodes
     -- have only partial assignments.
@@ -238,18 +241,18 @@ resolveWithFlags dom enabled os arch impl constrs trees checkDeps =
     build assigned ((fn, vals) : unassigned) =
       Node assigned $ map (\v -> build (insertFlagAssignment fn v assigned) unassigned) vals
 
-    tryAll :: [Either DepMapUnion a] -> Either DepMapUnion a
+    tryAll :: Monoid a => [Either a b] -> Either a b
     tryAll = foldr mp mz
 
     -- special version of `mplus' for our local purposes
-    mp :: Either DepMapUnion a -> Either DepMapUnion a -> Either DepMapUnion a
+    mp :: Monoid a => Either a b -> Either a b -> Either a b
     mp m@(Right _) _ = m
     mp _ m@(Right _) = m
     mp (Left xs) (Left ys) = Left (xs <> ys)
 
     -- `mzero'
-    mz :: Either DepMapUnion a
-    mz = Left (DepMapUnion Map.empty)
+    mz :: Monoid a => Either a b
+    mz = Left mempty
 
     env :: FlagAssignment -> FlagName -> Either FlagName Bool
     env flags flag = (maybe (Left flag) Right . lookupFlagAssignment flag) flags
@@ -323,27 +326,6 @@ extractConditions f gpkg =
     , extractCondition (f . benchmarkBuildInfo) . snd <$> condBenchmarks gpkg
     ]
 
--- | A map of package constraints that combines version ranges using 'unionVersionRanges'.
-newtype DepMapUnion = DepMapUnion {unDepMapUnion :: Map PackageName (VersionRange, NonEmptySet LibraryName)}
-
-instance Semigroup DepMapUnion where
-  DepMapUnion x <> DepMapUnion y =
-    DepMapUnion $
-      Map.unionWith unionVersionRanges' x y
-
-unionVersionRanges'
-  :: (VersionRange, NonEmptySet LibraryName)
-  -> (VersionRange, NonEmptySet LibraryName)
-  -> (VersionRange, NonEmptySet LibraryName)
-unionVersionRanges' (vr, cs) (vr', cs') = (unionVersionRanges vr vr', cs <> cs')
-
-toDepMapUnion :: [Dependency] -> DepMapUnion
-toDepMapUnion ds =
-  DepMapUnion $ Map.fromListWith unionVersionRanges' [(p, (vr, cs)) | Dependency p vr cs <- ds]
-
-fromDepMapUnion :: DepMapUnion -> [Dependency]
-fromDepMapUnion m = [Dependency p vr cs | (p, (vr, cs)) <- Map.toList (unDepMapUnion m)]
-
 freeVars :: CondTree ConfVar c a -> [FlagName]
 freeVars t = [f | PackageFlag f <- freeVars' t]
   where
@@ -453,7 +435,7 @@ finalizePD
   :: FlagAssignment
   -- ^ Explicitly specified flag assignments
   -> ComponentRequestedSpec
-  -> (Dependency -> Bool)
+  -> (Dependency -> DependencySatisfaction)
   -- ^ Is a given dependency satisfiable from the set of
   -- available packages?  If this is unknown then use
   -- True.
@@ -465,7 +447,7 @@ finalizePD
   -- ^ Additional constraints
   -> GenericPackageDescription
   -> Either
-      [Dependency]
+      [MissingDependency]
       (PackageDescription, FlagAssignment)
   -- ^ Either missing dependencies or the resolved package
   -- description along with the flag assignments chosen.
@@ -526,7 +508,11 @@ finalizePD
           | otherwise -> [b, not b]
       -- flagDefaults = map (\(n,x:_) -> (n,x)) flagChoices
       check ds =
-        let missingDeps = filter (not . satisfyDep) ds
+        let missingDeps =
+              [ MissingDependency dependency reason
+              | (dependency, Unsatisfied reason) <-
+                  map (\dependency -> (dependency, satisfyDep dependency)) ds
+              ]
          in if null missingDeps
               then DepOk
               else MissingDeps missingDeps
diff --git a/Cabal-syntax/src/Distribution/Pretty.hs b/Cabal-syntax/src/Distribution/Pretty.hs
index 3ddb806d81b..fcb0a7f0d0b 100644
--- a/Cabal-syntax/src/Distribution/Pretty.hs
+++ b/Cabal-syntax/src/Distribution/Pretty.hs
@@ -10,6 +10,8 @@ module Distribution.Pretty
   , showTokenStr
   , showFreeText
   , showFreeTextV3
+  , commaSpaceSep
+  , commaSep
 
     -- * Deprecated
   , Separator
@@ -118,3 +120,11 @@ lines_ s =
    in l : case s' of
         [] -> []
         (_ : s'') -> lines_ s''
+
+-- | Separate a list of documents by commas and spaces.
+commaSpaceSep :: Pretty a => [a] -> PP.Doc
+commaSpaceSep = PP.hsep . PP.punctuate PP.comma . map pretty
+
+-- | Separate a list of documents by commas.
+commaSep :: Pretty a => [a] -> PP.Doc
+commaSep = PP.hcat . PP.punctuate PP.comma . map pretty
diff --git a/Cabal-syntax/src/Distribution/Types/Dependency.hs b/Cabal-syntax/src/Distribution/Types/Dependency.hs
index 222a699a3f9..a152c9e3a68 100644
--- a/Cabal-syntax/src/Distribution/Types/Dependency.hs
+++ b/Cabal-syntax/src/Distribution/Types/Dependency.hs
@@ -78,31 +78,21 @@ instance NFData Dependency where rnf = genericRnf
 -- "pkg"
 --
 -- >>> prettyShow $ Dependency (mkPackageName "pkg") anyVersion $ NES.insert (LSubLibName $ mkUnqualComponentName "sublib") mainLibSet
--- "pkg:{pkg, sublib}"
+-- "pkg:{pkg,sublib}"
 --
 -- >>> prettyShow $ Dependency (mkPackageName "pkg") anyVersion $ NES.singleton (LSubLibName $ mkUnqualComponentName "sublib")
 -- "pkg:sublib"
 --
 -- >>> prettyShow $ Dependency (mkPackageName "pkg") anyVersion $ NES.insert (LSubLibName $ mkUnqualComponentName "sublib-b") $ NES.singleton (LSubLibName $ mkUnqualComponentName "sublib-a")
--- "pkg:{sublib-a, sublib-b}"
+-- "pkg:{sublib-a,sublib-b}"
 instance Pretty Dependency where
-  pretty (Dependency name ver sublibs) = withSubLibs (pretty name) <+> pver
+  pretty (Dependency name ver sublibs) = prettyLibraryNames name (NES.toNonEmpty sublibs) <+> pver
     where
       -- TODO: change to isAnyVersion after #6736
       pver
         | isAnyVersionLight ver = PP.empty
         | otherwise = pretty ver
 
-      withSubLibs doc = case NES.toList sublibs of
-        [LMainLibName] -> doc
-        [LSubLibName uq] -> doc <<>> PP.colon <<>> pretty uq
-        _ -> doc <<>> PP.colon <<>> PP.braces prettySublibs
-
-      prettySublibs = PP.hsep $ PP.punctuate PP.comma $ prettySublib <$> NES.toList sublibs
-
-      prettySublib LMainLibName = PP.text $ unPackageName name
-      prettySublib (LSubLibName un) = PP.text $ unUnqualComponentName un
-
 -- |
 --
 -- >>> simpleParsec "mylib:sub" :: Maybe Dependency
diff --git a/Cabal-syntax/src/Distribution/Types/DependencySatisfaction.hs b/Cabal-syntax/src/Distribution/Types/DependencySatisfaction.hs
new file mode 100644
index 00000000000..56ce74c1c45
--- /dev/null
+++ b/Cabal-syntax/src/Distribution/Types/DependencySatisfaction.hs
@@ -0,0 +1,14 @@
+module Distribution.Types.DependencySatisfaction
+  ( DependencySatisfaction (..)
+  ) where
+
+import Distribution.Types.MissingDependencyReason (MissingDependencyReason)
+
+-- | Whether or not a dependency constraint is satisfied.
+data DependencySatisfaction
+  = -- | The dependency constraint is satisfied.
+    Satisfied
+  | -- | The dependency constraint is not satisfied.
+    --
+    -- Includes a reason for explanation.
+    Unsatisfied MissingDependencyReason
diff --git a/Cabal-syntax/src/Distribution/Types/LibraryName.hs b/Cabal-syntax/src/Distribution/Types/LibraryName.hs
index 2b8f53f4f89..e31d1e82423 100644
--- a/Cabal-syntax/src/Distribution/Types/LibraryName.hs
+++ b/Cabal-syntax/src/Distribution/Types/LibraryName.hs
@@ -10,6 +10,7 @@ module Distribution.Types.LibraryName
   , libraryNameString
 
     -- * Pretty & Parse
+  , prettyLibraryNames
   , prettyLibraryNameComponent
   , parsecLibraryNameComponent
   ) where
@@ -21,6 +22,7 @@ import Distribution.Parsec
 import Distribution.Pretty
 import Distribution.Types.UnqualComponentName
 
+import qualified Data.List.NonEmpty as NEL
 import qualified Distribution.Compat.CharParsing as P
 import qualified Text.PrettyPrint as Disp
 
@@ -42,6 +44,22 @@ prettyLibraryNameComponent :: LibraryName -> Disp.Doc
 prettyLibraryNameComponent LMainLibName = Disp.text "lib"
 prettyLibraryNameComponent (LSubLibName str) = Disp.text "lib:" <<>> pretty str
 
+-- | Pretty print a 'LibraryName' after a package name.
+--
+-- Produces output like @foo@, @foo:bar@, or @foo:{bar,baz}@
+prettyLibraryNames :: Pretty a => a -> NonEmpty LibraryName -> Disp.Doc
+prettyLibraryNames package libraries =
+  let doc = pretty package
+
+      prettyComponent LMainLibName = pretty package
+      prettyComponent (LSubLibName component) = Disp.text $ unUnqualComponentName component
+
+      prettyComponents = commaSep $ prettyComponent <$> NEL.toList libraries
+   in case libraries of
+        LMainLibName :| [] -> doc
+        LSubLibName component :| [] -> doc <<>> Disp.colon <<>> pretty component
+        _ -> doc <<>> Disp.colon <<>> Disp.braces prettyComponents
+
 parsecLibraryNameComponent :: CabalParsing m => m LibraryName
 parsecLibraryNameComponent = do
   _ <- P.string "lib"
diff --git a/Cabal-syntax/src/Distribution/Types/MissingDependency.hs b/Cabal-syntax/src/Distribution/Types/MissingDependency.hs
new file mode 100644
index 00000000000..57d90276d8c
--- /dev/null
+++ b/Cabal-syntax/src/Distribution/Types/MissingDependency.hs
@@ -0,0 +1,34 @@
+module Distribution.Types.MissingDependency
+  ( MissingDependency (..)
+  ) where
+
+import Distribution.Compat.Prelude
+import Distribution.Pretty
+import Distribution.Types.Dependency
+  ( Dependency
+  , simplifyDependency
+  )
+import Distribution.Types.LibraryName
+  ( prettyLibraryNames
+  )
+import Distribution.Types.MissingDependencyReason
+  ( MissingDependencyReason (..)
+  )
+
+import qualified Text.PrettyPrint as PP
+
+-- | A missing dependency and information on why it's missing.
+data MissingDependency = MissingDependency Dependency MissingDependencyReason
+  deriving (Show)
+
+instance Pretty MissingDependency where
+  pretty (MissingDependency dependency reason) =
+    let prettyReason =
+          case reason of
+            MissingLibrary libraries ->
+              PP.text "missing" <+> prettyLibraryNames PP.empty libraries
+            MissingPackage -> PP.text "missing"
+            MissingComponent name -> PP.text "missing component" <+> pretty name
+            WrongVersion versions ->
+              PP.text "installed:" <+> commaSpaceSep versions
+     in pretty (simplifyDependency dependency) <+> PP.parens prettyReason
diff --git a/Cabal-syntax/src/Distribution/Types/MissingDependencyReason.hs b/Cabal-syntax/src/Distribution/Types/MissingDependencyReason.hs
new file mode 100644
index 00000000000..c1c37800f21
--- /dev/null
+++ b/Cabal-syntax/src/Distribution/Types/MissingDependencyReason.hs
@@ -0,0 +1,25 @@
+module Distribution.Types.MissingDependencyReason
+  ( MissingDependencyReason (..)
+  ) where
+
+import Data.List.NonEmpty (NonEmpty)
+import Distribution.Types.LibraryName (LibraryName)
+import Distribution.Types.PackageName (PackageName)
+import Distribution.Types.Version (Version)
+
+-- | A reason for a depency failing to solve.
+--
+-- This helps pinpoint dependencies that are installed with an incorrect
+-- version vs. dependencies that are not installed at all.
+data MissingDependencyReason
+  = -- | One or more libraries is missing.
+    MissingLibrary (NonEmpty LibraryName)
+  | -- | A package is not installed.
+    MissingPackage
+  | -- | A package is installed, but the versions don't match.
+    --
+    -- Contains the available versions.
+    WrongVersion [Version]
+  | -- | A component is not installed.
+    MissingComponent PackageName
+  deriving (Show)
diff --git a/Cabal-syntax/src/Distribution/Utils/Generic.hs b/Cabal-syntax/src/Distribution/Utils/Generic.hs
index 997e0132f5a..ca48c8e820a 100644
--- a/Cabal-syntax/src/Distribution/Utils/Generic.hs
+++ b/Cabal-syntax/src/Distribution/Utils/Generic.hs
@@ -100,11 +100,13 @@ import qualified Data.Set as Set
 
 import qualified Control.Exception as Exception
 import System.Directory
-  ( removeFile
+  ( copyFile
+  , getTemporaryDirectory
+  , removeFile
   , renameFile
   )
 import System.FilePath
-  ( splitFileName
+  ( takeFileName
   , (<.>)
   )
 import System.IO
@@ -153,8 +155,8 @@ wrapLine width = wrap 0 []
 
 -- | Gets the contents of a file, but guarantee that it gets closed.
 --
--- The file is read lazily but if it is not fully consumed by the action then
--- the remaining input is truncated and the file is closed.
+-- The file is read lazily; if it is not fully consumed by the action then an
+-- exception is thrown.
 withFileContents :: FilePath -> (String -> IO a) -> IO a
 withFileContents name action =
   withFile
@@ -167,18 +169,38 @@ withFileContents name action =
 -- The file is either written successfully or an IO exception is raised and
 -- the original file is left unchanged.
 --
--- On windows it is not possible to delete a file that is open by a process.
--- This case will give an IO exception but the atomic property is not affected.
+-- On Unix:
+--
+-- - If the temp directory (@$TMPDIR@) is in a filesystem different than the
+--   destination path, the renaming will be emulated via 'copyFile' then
+--   'deleteFile'.
+--
+-- On Windows:
+--
+-- - This operation is not guaranteed to be atomic, see 'renameFile'.
+--
+-- - It is not possible to delete a file that is open by a process. This case
+--   will give an IO exception but the atomic property is not affected.
+--
+-- - If the temp directory (@TMP@/@TEMP@/..., see haddocks on
+--   'getTemporaryDirectory') is in a different drive than the destination path,
+--   the write will be emulated via 'copyFile', then 'deleteFile'.
 writeFileAtomic :: FilePath -> LBS.ByteString -> IO ()
 writeFileAtomic targetPath content = do
-  let (targetDir, targetFile) = splitFileName targetPath
+  let targetFile = takeFileName targetPath
+  tmpDir <- getTemporaryDirectory
   Exception.bracketOnError
-    (openBinaryTempFileWithDefaultPermissions targetDir $ targetFile <.> "tmp")
+    (openBinaryTempFileWithDefaultPermissions tmpDir $ targetFile <.> "tmp")
     (\(tmpPath, handle) -> hClose handle >> removeFile tmpPath)
     ( \(tmpPath, handle) -> do
         LBS.hPut handle content
         hClose handle
-        renameFile tmpPath targetPath
+        Exception.catch
+          (renameFile tmpPath targetPath)
+          ( \(_ :: Exception.SomeException) -> do
+              copyFile tmpPath targetPath
+              removeFile tmpPath
+          )
     )
 
 -- ------------------------------------------------------------
diff --git a/Cabal-syntax/src/Distribution/Utils/Structured.hs b/Cabal-syntax/src/Distribution/Utils/Structured.hs
index 83ae28995a8..ec8463bd6d3 100644
--- a/Cabal-syntax/src/Distribution/Utils/Structured.hs
+++ b/Cabal-syntax/src/Distribution/Utils/Structured.hs
@@ -277,7 +277,7 @@ structuredDecodeOrFailIO :: (Binary.Binary a, Structured a) => LBS.ByteString ->
 structuredDecodeOrFailIO bs =
   catch (evaluate (structuredDecode bs) >>= return . Right) handler
   where
-    handler (ErrorCallWithLocation str _) = return $ Left str
+    handler (ErrorCall str) = return $ Left str
 
 -- | Lazily reconstruct a value previously written to a file.
 structuredDecodeFileOrFail :: (Binary.Binary a, Structured a) => FilePath -> IO (Either String a)
diff --git a/Cabal-tests/tests/ParserTests/regressions/issue-5846.format b/Cabal-tests/tests/ParserTests/regressions/issue-5846.format
index 749a9c20524..93e53fc48bd 100644
--- a/Cabal-tests/tests/ParserTests/regressions/issue-5846.format
+++ b/Cabal-tests/tests/ParserTests/regressions/issue-5846.format
@@ -5,7 +5,7 @@ version:       5846
 library
     default-language: Haskell2010
     build-depends:
-        lib1:{a, b},
+        lib1:{a,b},
         lib2:c,
         lib3:d >=1,
-        lib4:{a, b} >=1
+        lib4:{a,b} >=1
diff --git a/Cabal-tests/tests/UnitTests/Distribution/Simple/Utils.hs b/Cabal-tests/tests/UnitTests/Distribution/Simple/Utils.hs
index 2e544c8c52d..48e8aae9c1d 100644
--- a/Cabal-tests/tests/UnitTests/Distribution/Simple/Utils.hs
+++ b/Cabal-tests/tests/UnitTests/Distribution/Simple/Utils.hs
@@ -23,16 +23,14 @@ import Test.Tasty.HUnit
 withTempFileTest :: Assertion
 withTempFileTest = do
   fileName <- newIORef ""
-  tempDir  <- getTemporaryDirectory
-  withTempFile tempDir ".foo" $ \fileName' _handle -> do
+  withTempFile ".foo" $ \fileName' _handle -> do
     writeIORef fileName fileName'
   fileExists <- readIORef fileName >>= doesFileExist
   assertBool "Temporary file not deleted by 'withTempFile'!" (not fileExists)
 
 withTempFileRemovedTest :: Assertion
 withTempFileRemovedTest = do
-  tempDir <- getTemporaryDirectory
-  withTempFile tempDir ".foo" $ \fileName handle -> do
+  withTempFile ".foo" $ \fileName handle -> do
     hClose handle
     removeFile fileName
 
@@ -58,9 +56,8 @@ rawSystemStdInOutTextDecodingTest ghcPath
     -- so skip the test if it's not.
     | show localeEncoding /= "UTF-8" = return ()
     | otherwise = do
-  tempDir  <- getTemporaryDirectory
-  res <- withTempFile tempDir ".hs" $ \filenameHs handleHs -> do
-    withTempFile tempDir ".exe" $ \filenameExe handleExe -> do
+  res <- withTempFile ".hs" $ \filenameHs handleHs -> do
+    withTempFile ".exe" $ \filenameExe handleExe -> do
       -- Small program printing not utf8
       hPutStrLn handleHs "import Data.ByteString"
       hPutStrLn handleHs "main = Data.ByteString.putStr (Data.ByteString.pack [32, 32, 255])"
diff --git a/Cabal/Cabal.cabal b/Cabal/Cabal.cabal
index b9a7e0838ab..a9e108d1f7b 100644
--- a/Cabal/Cabal.cabal
+++ b/Cabal/Cabal.cabal
@@ -248,6 +248,7 @@ library
     Distribution.Types.ConfVar,
     Distribution.Types.Dependency,
     Distribution.Types.DependencyMap,
+    Distribution.Types.DependencySatisfaction,
     Distribution.Types.ExeDependency,
     Distribution.Types.Executable,
     Distribution.Types.Executable.Lens,
@@ -271,6 +272,8 @@ library
     Distribution.Types.Library.Lens,
     Distribution.Types.LibraryName,
     Distribution.Types.LibraryVisibility,
+    Distribution.Types.MissingDependency,
+    Distribution.Types.MissingDependencyReason,
     Distribution.Types.Mixin,
     Distribution.Types.Module,
     Distribution.Types.ModuleReexport,
diff --git a/Cabal/src/Distribution/Simple.hs b/Cabal/src/Distribution/Simple.hs
index ada1d6c7aad..3533cf78336 100644
--- a/Cabal/src/Distribution/Simple.hs
+++ b/Cabal/src/Distribution/Simple.hs
@@ -1094,6 +1094,7 @@ defaultInstallHook_setupHooks inst_hooks pkg_descr localbuildinfo _ flags = do
         defaultRegisterFlags
           { regInPlace = installInPlace flags
           , regPackageDB = installPackageDB flags
+          , registerCommonFlags = installCommonFlags flags
           }
   when (hasLibs pkg_descr) $
     register pkg_descr localbuildinfo registerFlags
diff --git a/Cabal/src/Distribution/Simple/Configure.hs b/Cabal/src/Distribution/Simple/Configure.hs
index 033f3c9de54..56d8517b3b9 100644
--- a/Cabal/src/Distribution/Simple/Configure.hs
+++ b/Cabal/src/Distribution/Simple/Configure.hs
@@ -106,9 +106,11 @@ import qualified Distribution.Simple.SetupHooks.Internal as SetupHooks
 import Distribution.Simple.Utils
 import Distribution.System
 import Distribution.Types.ComponentRequestedSpec
+import Distribution.Types.DependencySatisfaction (DependencySatisfaction (..))
 import Distribution.Types.GivenComponent
 import qualified Distribution.Types.LocalBuildConfig as LBC
 import Distribution.Types.LocalBuildInfo
+import Distribution.Types.MissingDependencyReason (MissingDependencyReason (..))
 import Distribution.Types.PackageVersionConstraint
 import Distribution.Utils.LogProgress
 import Distribution.Utils.NubList
@@ -154,7 +156,6 @@ import System.Directory
   ( canonicalizePath
   , createDirectoryIfMissing
   , doesFileExist
-  , getTemporaryDirectory
   , removeFile
   )
 import System.FilePath
@@ -1480,7 +1481,7 @@ dependencySatisfiable
   -> Map (PackageName, ComponentName) PromisedComponent
   -> Map (PackageName, ComponentName) InstalledPackageInfo
   -- ^ required dependencies
-  -> (Dependency -> Bool)
+  -> (Dependency -> DependencySatisfaction)
 dependencySatisfiable
   use_external_internal_deps
   exact_config
@@ -1506,16 +1507,14 @@ dependencySatisfiable
             internalDepSatisfiable
           else -- Backward compatibility for the old sublibrary syntax
 
-            ( sublibs == mainLibSet
-                && Map.member
-                  ( pn
-                  , CLibName $
-                      LSubLibName $
-                        packageNameToUnqualComponentName depName
-                  )
-                  requiredDepsMap
-            )
-              || all visible sublibs
+            let depComponentName =
+                  CLibName $ LSubLibName $ packageNameToUnqualComponentName depName
+                invisibleLibraries = NES.filter (not . visible) sublibs
+             in if sublibs == mainLibSet && Map.member (pn, depComponentName) requiredDepsMap
+                  then Satisfied
+                  else case nonEmpty $ Set.toList invisibleLibraries of
+                    Nothing -> Satisfied
+                    Just invisibleLibraries' -> Unsatisfied $ MissingLibrary invisibleLibraries'
     | isInternalDep =
         if use_external_internal_deps
           then -- When we are doing per-component configure, we now need to
@@ -1532,12 +1531,31 @@ dependencySatisfiable
       isInternalDep = pn == depName
 
       depSatisfiable =
-        not . null $ PackageIndex.lookupDependency installedPackageSet depName vr
+        let allVersions = PackageIndex.lookupPackageName installedPackageSet depName
+            eligibleVersions =
+              [ version
+              | (version, _infos) <- PackageIndex.eligibleDependencies allVersions
+              ]
+         in if null $ PackageIndex.matchingDependencies vr allVersions
+              then
+                if null eligibleVersions
+                  then Unsatisfied $ MissingPackage
+                  else Unsatisfied $ WrongVersion eligibleVersions
+              else Satisfied
 
       internalDepSatisfiable =
-        Set.isSubsetOf (NES.toSet sublibs) packageLibraries
+        let missingLibraries = (NES.toSet sublibs) `Set.difference` packageLibraries
+         in case nonEmpty $ Set.toList missingLibraries of
+              Nothing -> Satisfied
+              Just missingLibraries' -> Unsatisfied $ MissingLibrary missingLibraries'
+
       internalDepSatisfiableExternally =
-        all (\ln -> not $ null $ PackageIndex.lookupInternalDependency installedPackageSet pn vr ln) sublibs
+        -- TODO: Might need to propagate information on which versions _are_ available, if any...
+        let missingLibraries =
+              NES.filter (null . PackageIndex.lookupInternalDependency installedPackageSet pn vr) sublibs
+         in case nonEmpty $ Set.toList missingLibraries of
+              Nothing -> Satisfied
+              Just missingLibraries' -> Unsatisfied $ MissingLibrary missingLibraries'
 
       -- Check whether a library exists and is visible.
       -- We don't disambiguate between dependency on non-existent or private
@@ -1572,7 +1590,7 @@ configureFinalizedPackage
   -> ConfigFlags
   -> ComponentRequestedSpec
   -> [PackageVersionConstraint]
-  -> (Dependency -> Bool)
+  -> (Dependency -> DependencySatisfaction)
   -- ^ tests if a dependency is satisfiable.
   -- Might say it's satisfiable even when not.
   -> Compiler
@@ -2674,10 +2692,9 @@ checkForeignDeps pkg lbi verbosity =
 
     builds :: String -> [ProgArg] -> IO Bool
     builds program args =
-      do
-        tempDir <- makeSymbolicPath <$> getTemporaryDirectory
-        withTempFileCwd mbWorkDir tempDir ".c" $ \cName cHnd ->
-          withTempFileCwd mbWorkDir tempDir "" $ \oNname oHnd -> do
+      withTempFileCwd ".c" $ \cName cHnd ->
+        withTempFileCwd "" $ \oNname oHnd ->
+          do
             hPutStrLn cHnd program
             hClose cHnd
             hClose oHnd
@@ -2689,8 +2706,8 @@ checkForeignDeps pkg lbi verbosity =
                 (withPrograms lbi)
                 (getSymbolicPath cName : "-o" : getSymbolicPath oNname : args)
             return True
-        `catchIO` (\_ -> return False)
-        `catchExit` (\_ -> return False)
+            `catchIO` (\_ -> return False)
+            `catchExit` (\_ -> return False)
 
     explainErrors Nothing [] = return () -- should be impossible!
     explainErrors _ _
diff --git a/Cabal/src/Distribution/Simple/Errors.hs b/Cabal/src/Distribution/Simple/Errors.hs
index c1cc75b5ad1..253b2f0dfbe 100644
--- a/Cabal/src/Distribution/Simple/Errors.hs
+++ b/Cabal/src/Distribution/Simple/Errors.hs
@@ -31,6 +31,7 @@ import Distribution.Simple.InstallDirs
 import Distribution.Simple.PreProcess.Types (Suffix)
 import Distribution.Simple.SetupHooks.Errors
 import Distribution.System (OS)
+import Distribution.Types.MissingDependency (MissingDependency)
 import Distribution.Types.VersionRange.Internal ()
 import Distribution.Version
 import Text.PrettyPrint
@@ -126,7 +127,7 @@ data CabalException
   | CantFindForeignLibraries [String]
   | ExpectedAbsoluteDirectory FilePath
   | FlagsNotSpecified [FlagName]
-  | EncounteredMissingDependency [Dependency]
+  | EncounteredMissingDependency [MissingDependency]
   | CompilerDoesn'tSupportThinning
   | CompilerDoesn'tSupportReexports
   | CompilerDoesn'tSupportBackpack
@@ -552,7 +553,7 @@ exceptionMessage e = case e of
             . nest 4
             . sep
             . punctuate comma
-            . map (pretty . simplifyDependency)
+            . map pretty
             $ missing
          )
   CompilerDoesn'tSupportThinning ->
diff --git a/Cabal/src/Distribution/Simple/GHC/Build.hs b/Cabal/src/Distribution/Simple/GHC/Build.hs
index 1972e9d903f..c12fb7b2427 100644
--- a/Cabal/src/Distribution/Simple/GHC/Build.hs
+++ b/Cabal/src/Distribution/Simple/GHC/Build.hs
@@ -12,7 +12,7 @@ import Distribution.Simple.Flag (Flag)
 import Distribution.Simple.GHC.Build.ExtraSources
 import Distribution.Simple.GHC.Build.Link
 import Distribution.Simple.GHC.Build.Modules
-import Distribution.Simple.GHC.Build.Utils (isHaskell)
+import Distribution.Simple.GHC.Build.Utils (compilerBuildWay, isHaskell)
 import Distribution.Simple.LocalBuildInfo
 import Distribution.Simple.Program.Builtin (ghcProgram)
 import Distribution.Simple.Program.Db (requireProgram)
@@ -73,6 +73,7 @@ build numJobs pkg_descr pbci = do
     verbosity = buildVerbosity pbci
     isLib = buildIsLib pbci
     lbi = localBuildInfo pbci
+    bi = buildBI pbci
     clbi = buildCLBI pbci
     isIndef = componentIsIndefinite clbi
     mbWorkDir = mbWorkDirLBI lbi
@@ -111,9 +112,22 @@ build numJobs pkg_descr pbci = do
 
   (ghcProg, _) <- liftIO $ requireProgram verbosity ghcProgram (withPrograms lbi)
 
+  -- Ways which are wanted from configuration flags
   let wantedWays@(wantedLibWays, _, wantedExeWay) = buildWays lbi
 
-  liftIO $ info verbosity ("Wanted build ways(" ++ show isLib ++ "): " ++ show (if isLib then wantedLibWays isIndef else [wantedExeWay]))
+  -- Ways which are needed due to the compiler configuration
+  let doingTH = usesTemplateHaskellOrQQ bi
+      defaultGhcWay = compilerBuildWay (buildCompiler pbci)
+      wantedLibBuildWays =
+        if isLib
+          then wantedLibWays isIndef
+          else [wantedExeWay]
+      finalLibBuildWays =
+        wantedLibBuildWays
+          ++ [defaultGhcWay | doingTH && defaultGhcWay `notElem` wantedLibBuildWays]
+
+  liftIO $ info verbosity ("Wanted build ways(" ++ show isLib ++ "): " ++ show wantedLibBuildWays)
+  liftIO $ info verbosity ("Final lib build ways(" ++ show isLib ++ "): " ++ show finalLibBuildWays)
   -- We need a separate build and link phase, and C sources must be compiled
   -- after Haskell modules, because C sources may depend on stub headers
   -- generated from compiling Haskell modules (#842, #3294).
@@ -127,7 +141,7 @@ build numJobs pkg_descr pbci = do
             | otherwise ->
                 (Nothing, Just mainFile)
           Nothing -> (Nothing, Nothing)
-  buildOpts <- buildHaskellModules numJobs ghcProg hsMainFile inputModules buildTargetDir (wantedLibWays isIndef) pbci
+  buildOpts <- buildHaskellModules numJobs ghcProg hsMainFile inputModules buildTargetDir finalLibBuildWays pbci
   extraSources <- buildAllExtraSources nonHsMainFile ghcProg buildTargetDir wantedWays pbci
   linkOrLoadComponent
     ghcProg
diff --git a/Cabal/src/Distribution/Simple/GHC/Build/Link.hs b/Cabal/src/Distribution/Simple/GHC/Build/Link.hs
index 3f9f00c9d28..ef9f33d79c9 100644
--- a/Cabal/src/Distribution/Simple/GHC/Build/Link.hs
+++ b/Cabal/src/Distribution/Simple/GHC/Build/Link.hs
@@ -735,7 +735,9 @@ runReplOrWriteFlags ghcProg lbi rflags ghcOpts pkg_name target =
         Flag out_dir -> do
           let uid = componentUnitId clbi
               this_unit = prettyShow uid
-              reexported_modules = [mn | LibComponentLocalBuildInfo{} <- [clbi], IPI.ExposedModule mn (Just{}) <- componentExposedModules clbi]
+              reexported_modules =
+                [ mn | LibComponentLocalBuildInfo{componentExposedModules = exposed_mods} <- [clbi], IPI.ExposedModule mn (Just{}) <- exposed_mods
+                ]
               hidden_modules = otherModules bi
               extra_opts =
                 concat $
diff --git a/Cabal/src/Distribution/Simple/GHC/Internal.hs b/Cabal/src/Distribution/Simple/GHC/Internal.hs
index 0686f30ba1b..6e27b41bc83 100644
--- a/Cabal/src/Distribution/Simple/GHC/Internal.hs
+++ b/Cabal/src/Distribution/Simple/GHC/Internal.hs
@@ -85,7 +85,7 @@ import Distribution.Utils.Path
 import Distribution.Verbosity
 import Distribution.Version (Version)
 import Language.Haskell.Extension
-import System.Directory (getDirectoryContents, getTemporaryDirectory)
+import System.Directory (getDirectoryContents)
 import System.Environment (getEnv)
 import System.FilePath
   ( takeDirectory
@@ -221,9 +221,8 @@ configureToolchain _implInfo ghcProg ghcInfo =
     -- we need to find out if ld supports the -x flag
     configureLd' :: Verbosity -> ConfiguredProgram -> IO ConfiguredProgram
     configureLd' verbosity ldProg = do
-      tempDir <- getTemporaryDirectory
-      ldx <- withTempFile tempDir ".c" $ \testcfile testchnd ->
-        withTempFile tempDir ".o" $ \testofile testohnd -> do
+      ldx <- withTempFile ".c" $ \testcfile testchnd ->
+        withTempFile ".o" $ \testofile testohnd -> do
           hPutStrLn testchnd "int foo() { return 0; }"
           hClose testchnd
           hClose testohnd
@@ -236,7 +235,7 @@ configureToolchain _implInfo ghcProg ghcInfo =
             , "-o"
             , testofile
             ]
-          withTempFile tempDir ".o" $ \testofile' testohnd' ->
+          withTempFile ".o" $ \testofile' testohnd' ->
             do
               hClose testohnd'
               _ <-
diff --git a/Cabal/src/Distribution/Simple/Haddock.hs b/Cabal/src/Distribution/Simple/Haddock.hs
index ba025a85549..ec4e60ff685 100644
--- a/Cabal/src/Distribution/Simple/Haddock.hs
+++ b/Cabal/src/Distribution/Simple/Haddock.hs
@@ -1133,8 +1133,6 @@ renderArgs verbosity mbWorkDir tmpFileOpts version comp platform args k = do
                 withResponseFile
                   verbosity
                   tmpFileOpts
-                  mbWorkDir
-                  outputDir
                   "haddock-response.txt"
                   (if haddockSupportsUTF8 then Just utf8 else Nothing)
                   renderedArgs
@@ -1144,7 +1142,7 @@ renderArgs verbosity mbWorkDir tmpFileOpts version comp platform args k = do
     (Flag pfile, _) ->
       withPrologueArgs ["--prologue=" ++ pfile]
     (_, Flag prologueText) ->
-      withTempFileEx tmpFileOpts mbWorkDir outputDir "haddock-prologue.txt" $
+      withTempFileEx tmpFileOpts "haddock-prologue.txt" $
         \prologueFileName h -> do
           when haddockSupportsUTF8 (hSetEncoding h utf8)
           hPutStrLn h prologueText
diff --git a/Cabal/src/Distribution/Simple/PackageIndex.hs b/Cabal/src/Distribution/Simple/PackageIndex.hs
index 927e10ae878..e6944430755 100644
--- a/Cabal/src/Distribution/Simple/PackageIndex.hs
+++ b/Cabal/src/Distribution/Simple/PackageIndex.hs
@@ -68,6 +68,7 @@ module Distribution.Simple.PackageIndex
   , lookupSourcePackageId
   , lookupPackageId
   , lookupPackageName
+  , lookupInternalPackageName
   , lookupDependency
   , lookupInternalDependency
 
@@ -93,6 +94,10 @@ module Distribution.Simple.PackageIndex
   , dependencyCycles
   , dependencyGraph
   , moduleNameIndex
+
+    -- ** Filters on lookup results
+  , eligibleDependencies
+  , matchingDependencies
   ) where
 
 import qualified Data.Map.Strict as Map
@@ -474,7 +479,18 @@ lookupPackageName
   -> [(Version, [a])]
 lookupPackageName index name =
   -- Do not match internal libraries
-  case Map.lookup (name, LMainLibName) (packageIdIndex index) of
+  lookupInternalPackageName index name LMainLibName
+
+-- | Does a lookup by source package name and library name.
+--
+-- Also looks up internal packages.
+lookupInternalPackageName
+  :: PackageIndex a
+  -> PackageName
+  -> LibraryName
+  -> [(Version, [a])]
+lookupInternalPackageName index name library =
+  case Map.lookup (name, library) (packageIdIndex index) of
     Nothing -> []
     Just pvers -> Map.toList pvers
 
@@ -509,23 +525,46 @@ lookupInternalDependency
   -> LibraryName
   -> [(Version, [IPI.InstalledPackageInfo])]
 lookupInternalDependency index name versionRange libn =
-  case Map.lookup (name, libn) (packageIdIndex index) of
-    Nothing -> []
-    Just pvers ->
-      [ (ver, pkgs')
-      | (ver, pkgs) <- Map.toList pvers
-      , ver `withinRange` versionRange
-      , let pkgs' = filter eligible pkgs
-      , -- Enforce the invariant
-      not (null pkgs')
-      ]
+  matchingDependencies versionRange $
+    lookupInternalPackageName index name libn
+
+-- | Filter a set of installed packages to ones eligible as dependencies.
+--
+-- When we select for dependencies, we ONLY want to pick up indefinite
+-- packages, or packages with no instantiations.  We'll do mix-in linking to
+-- improve any such package into an instantiated one later.
+--
+-- INVARIANT: List of eligible 'IPI.InstalledPackageInfo' is non-empty.
+eligibleDependencies
+  :: [(Version, [IPI.InstalledPackageInfo])]
+  -> [(Version, [IPI.InstalledPackageInfo])]
+eligibleDependencies versions =
+  [ (ver, pkgs')
+  | (ver, pkgs) <- versions
+  , let pkgs' = filter eligible pkgs
+  , -- Enforce the invariant
+  not (null pkgs')
+  ]
   where
-    -- When we select for dependencies, we ONLY want to pick up indefinite
-    -- packages, or packages with no instantiations.  We'll do mix-in
-    -- linking to improve any such package into an instantiated one
-    -- later.
     eligible pkg = IPI.indefinite pkg || null (IPI.instantiatedWith pkg)
 
+-- | Get eligible dependencies from a list of versions.
+--
+-- This can be used to filter the output of 'lookupPackageName' or
+-- 'lookupInternalPackageName'.
+--
+-- INVARIANT: List of eligible 'IPI.InstalledPackageInfo' is non-empty.
+matchingDependencies
+  :: VersionRange
+  -> [(Version, [IPI.InstalledPackageInfo])]
+  -> [(Version, [IPI.InstalledPackageInfo])]
+matchingDependencies versionRange versions =
+  let eligibleVersions = eligibleDependencies versions
+   in [ (ver, pkgs)
+      | (ver, pkgs) <- eligibleVersions
+      , ver `withinRange` versionRange
+      ]
+
 --
 
 -- * Case insensitive name lookups
diff --git a/Cabal/src/Distribution/Simple/PreProcess.hs b/Cabal/src/Distribution/Simple/PreProcess.hs
index 61dd8163733..e56627893c1 100644
--- a/Cabal/src/Distribution/Simple/PreProcess.hs
+++ b/Cabal/src/Distribution/Simple/PreProcess.hs
@@ -511,8 +511,6 @@ ppHsc2hs bi lbi clbi =
             withResponseFile
               verbosity
               defaultTempFileOptions
-              mbWorkDir
-              (makeSymbolicPath $ takeDirectory outFile)
               "hsc2hs-response.txt"
               Nothing
               pureArgs
diff --git a/Cabal/src/Distribution/Simple/Program/Ar.hs b/Cabal/src/Distribution/Simple/Program/Ar.hs
index 004b02cca1a..2e9b432385f 100644
--- a/Cabal/src/Distribution/Simple/Program/Ar.hs
+++ b/Cabal/src/Distribution/Simple/Program/Ar.hs
@@ -154,7 +154,7 @@ createArLibArchive verbosity lbi targetPath files = do
                 (initial, middle, final)
                 (map getSymbolicPath files)
           ]
-      else withResponseFile verbosity defaultTempFileOptions mbWorkDir tmpDir "ar.rsp" Nothing (map getSymbolicPath files) $
+      else withResponseFile verbosity defaultTempFileOptions "ar.rsp" Nothing (map getSymbolicPath files) $
         \path -> runProgramInvocation verbosity $ invokeWithResponseFile path
 
     unless
diff --git a/Cabal/src/Distribution/Simple/Program/Ld.hs b/Cabal/src/Distribution/Simple/Program/Ld.hs
index 5c2a33809ae..00ed5d182d7 100644
--- a/Cabal/src/Distribution/Simple/Program/Ld.hs
+++ b/Cabal/src/Distribution/Simple/Program/Ld.hs
@@ -83,8 +83,6 @@ combineObjectFiles verbosity lbi ldProg target files = do
     middle = ld middleArgs
     final = ld finalArgs
 
-    targetDir = takeDirectorySymbolicPath target
-
     invokeWithResponseFile :: FilePath -> ProgramInvocation
     invokeWithResponseFile atFile =
       ld $ simpleArgs ++ ['@' : atFile]
@@ -106,7 +104,7 @@ combineObjectFiles verbosity lbi ldProg target files = do
 
   if oldVersionManualOverride || responseArgumentsNotSupported
     then run $ multiStageProgramInvocation simple (initial, middle, final) (map getSymbolicPath files)
-    else withResponseFile verbosity defaultTempFileOptions mbWorkDir targetDir "ld.rsp" Nothing (map getSymbolicPath files) $
+    else withResponseFile verbosity defaultTempFileOptions "ld.rsp" Nothing (map getSymbolicPath files) $
       \path -> runProgramInvocation verbosity $ invokeWithResponseFile path
   where
     tmpfile = target <.> "tmp" -- perhaps should use a proper temp file
diff --git a/Cabal/src/Distribution/Simple/Program/ResponseFile.hs b/Cabal/src/Distribution/Simple/Program/ResponseFile.hs
index ee8271545f1..dec6cb0ae50 100644
--- a/Cabal/src/Distribution/Simple/Program/ResponseFile.hs
+++ b/Cabal/src/Distribution/Simple/Program/ResponseFile.hs
@@ -27,10 +27,6 @@ import Distribution.Verbosity
 withResponseFile
   :: Verbosity
   -> TempFileOptions
-  -> Maybe (SymbolicPath CWD (Dir Pkg))
-  -- ^ Working directory
-  -> SymbolicPath Pkg (Dir Response)
-  -- ^ Directory to create response file in.
   -> String
   -- ^ Template for response file name.
   -> Maybe TextEncoding
@@ -39,8 +35,8 @@ withResponseFile
   -- ^ Arguments to put into response file.
   -> (FilePath -> IO a)
   -> IO a
-withResponseFile verbosity tmpFileOpts mbWorkDir responseDir fileNameTemplate encoding arguments f =
-  withTempFileEx tmpFileOpts mbWorkDir responseDir fileNameTemplate $ \responsePath hf -> do
+withResponseFile verbosity tmpFileOpts fileNameTemplate encoding arguments f =
+  withTempFileEx tmpFileOpts fileNameTemplate $ \responsePath hf -> do
     let responseFileName = getSymbolicPath responsePath
     traverse_ (hSetEncoding hf) encoding
     let responseContents =
diff --git a/Cabal/src/Distribution/Simple/Utils.hs b/Cabal/src/Distribution/Simple/Utils.hs
index 3688f602759..d51601e5c27 100644
--- a/Cabal/src/Distribution/Simple/Utils.hs
+++ b/Cabal/src/Distribution/Simple/Utils.hs
@@ -250,6 +250,7 @@ import System.Directory
   , getDirectoryContents
   , getModificationTime
   , getPermissions
+  , getTemporaryDirectory
   , removeDirectoryRecursive
   , removeFile
   )
@@ -1733,23 +1734,17 @@ defaultTempFileOptions = TempFileOptions{optKeepTempFiles = False}
 
 -- | Use a temporary filename that doesn't already exist
 withTempFile
-  :: FilePath
-  -- ^ Temp dir to create the file in
-  -> String
+  :: String
   -- ^ File name template. See 'openTempFile'.
   -> (FilePath -> Handle -> IO a)
   -> IO a
-withTempFile tmpDir template f = withFrozenCallStack $
-  withTempFileCwd Nothing (makeSymbolicPath tmpDir) template $
+withTempFile template f = withFrozenCallStack $
+  withTempFileCwd template $
     \fp h -> f (getSymbolicPath fp) h
 
 -- | Use a temporary filename that doesn't already exist.
 withTempFileCwd
-  :: Maybe (SymbolicPath CWD (Dir Pkg))
-  -- ^ Working directory
-  -> SymbolicPath Pkg (Dir tmpDir)
-  -- ^ Temp dir to create the file in
-  -> String
+  :: String
   -- ^ File name template. See 'openTempFile'.
   -> (SymbolicPath Pkg File -> Handle -> IO a)
   -> IO a
@@ -1758,20 +1753,17 @@ withTempFileCwd = withFrozenCallStack $ withTempFileEx defaultTempFileOptions
 -- | A version of 'withTempFile' that additionally takes a 'TempFileOptions'
 -- argument.
 withTempFileEx
-  :: forall a tmpDir
+  :: forall a
    . TempFileOptions
-  -> Maybe (SymbolicPath CWD (Dir Pkg))
-  -- ^ Working directory
-  -> SymbolicPath Pkg (Dir tmpDir)
-  -- ^ Temp dir to create the file in
   -> String
   -- ^ File name template. See 'openTempFile'.
   -> (SymbolicPath Pkg File -> Handle -> IO a)
   -> IO a
-withTempFileEx opts mbWorkDir tmpDir template action =
+withTempFileEx opts template action = do
+  tmp <- getTemporaryDirectory
   withFrozenCallStack $
     Exception.bracket
-      (openTempFile (i tmpDir) template)
+      (openTempFile tmp template)
       ( \(name, handle) -> do
           hClose handle
           unless (optKeepTempFiles opts) $
@@ -1779,12 +1771,11 @@ withTempFileEx opts mbWorkDir tmpDir template action =
               removeFile $
                 name
       )
-      (withLexicalCallStack (\(fn, h) -> action (mkRelToPkg fn) h))
+      (withLexicalCallStack (\(fn, h) -> action (mkRelToPkg tmp fn) h))
   where
-    i = interpretSymbolicPath mbWorkDir -- See Note [Symbolic paths] in Distribution.Utils.Path
-    mkRelToPkg :: FilePath -> SymbolicPath Pkg File
-    mkRelToPkg fp =
-      tmpDir </> makeRelativePathEx (takeFileName fp)
+    mkRelToPkg :: FilePath -> FilePath -> SymbolicPath Pkg File
+    mkRelToPkg tmp fp =
+      makeSymbolicPath tmp </> makeRelativePathEx (takeFileName fp)
 
 -- 'openTempFile' returns a path of the form @i tmpDir </> fn@, but we
 -- want 'withTempFileEx' to return @tmpDir </> fn@. So we split off
diff --git a/Makefile b/Makefile
index 7b272c55e09..12d38557de6 100644
--- a/Makefile
+++ b/Makefile
@@ -29,18 +29,26 @@ init: ## Set up git hooks and ignored revisions
 
 .PHONY: style
 style: ## Run the code styler
-	@fourmolu -q -i Cabal Cabal-syntax cabal-install
+	@fourmolu -q -i Cabal Cabal-syntax cabal-install cabal-validate
 
 .PHONY: style-modified
 style-modified: ## Run the code styler on modified files
-	@git ls-files --modified Cabal Cabal-syntax cabal-install \
+	@git ls-files --modified Cabal Cabal-syntax cabal-install cabal-validate \
 		| grep '.hs$$' | xargs -P $(PROCS) -I {} fourmolu -q -i {}
 
 .PHONY: style-commit
 style-commit: ## Run the code styler on the previous commit
-	@git diff --name-only HEAD $(COMMIT) Cabal Cabal-syntax cabal-install \
+	@git diff --name-only HEAD $(COMMIT) Cabal Cabal-syntax cabal-install cabal-validate \
 		| grep '.hs$$' | xargs -P $(PROCS) -I {} fourmolu -q -i {}
 
+.PHONY: whitespace
+whitespace: ## Run fix-whitespace in check mode
+	fix-whitespace --check --verbose
+
+.PHONY: fix-whitespace
+fix-whitespace: ## Run fix-whitespace in fix mode
+	fix-whitespace --verbose
+
 # source generation: SPDX
 
 SPDX_LICENSE_HS:=Cabal-syntax/src/Distribution/SPDX/LicenseId.hs
diff --git a/cabal-install/src/Distribution/Client/CmdOutdated.hs b/cabal-install/src/Distribution/Client/CmdOutdated.hs
index ed40a1a85e6..7674e67286f 100644
--- a/cabal-install/src/Distribution/Client/CmdOutdated.hs
+++ b/cabal-install/src/Distribution/Client/CmdOutdated.hs
@@ -129,6 +129,9 @@ import Distribution.Types.ComponentRequestedSpec
 import Distribution.Types.Dependency
   ( Dependency (..)
   )
+import Distribution.Types.DependencySatisfaction
+  ( DependencySatisfaction (..)
+  )
 import Distribution.Types.PackageVersionConstraint
   ( PackageVersionConstraint (..)
   , simplifyPackageVersionConstraint
@@ -443,7 +446,7 @@ depsFromPkgDesc verbosity comp platform = do
         finalizePD
           mempty
           (ComponentRequestedSpec True True)
-          (const True)
+          (const Satisfied)
           platform
           cinfo
           []
diff --git a/cabal-install/src/Distribution/Client/Config.hs b/cabal-install/src/Distribution/Client/Config.hs
index 2faf9e1756d..f7b01512ca4 100644
--- a/cabal-install/src/Distribution/Client/Config.hs
+++ b/cabal-install/src/Distribution/Client/Config.hs
@@ -160,6 +160,7 @@ import qualified Distribution.Deprecated.ParseUtils as ParseUtils
 import Distribution.Parsec (ParsecParser, parsecFilePath, parsecOptCommaList, parsecToken)
 import Distribution.Simple.Command
   ( CommandUI (commandOptions)
+  , OptionField
   , ShowOrParseArgs (..)
   , commandDefaultFlags
   )
@@ -1314,6 +1315,19 @@ configFieldDescriptions src =
             ParseArgs
        ]
   where
+    toSavedConfig
+      :: (FieldDescr a -> FieldDescr SavedConfig)
+      -- Lifting function.
+      -> [OptionField a]
+      -- Option fields.
+      -> [String]
+      -- Fields to exclude, by name.
+      -> [FieldDescr a]
+      -- Field replacements.
+      --
+      -- If an option is found with the same name as one of these replacement
+      -- fields, the replacement field is used instead of the option.
+      -> [FieldDescr SavedConfig]
     toSavedConfig lift options exclusions replacements =
       [ lift (fromMaybe field replacement)
       | opt <- options
diff --git a/cabal-install/src/Distribution/Client/Configure.hs b/cabal-install/src/Distribution/Client/Configure.hs
index 6634f874071..5f82329eb52 100644
--- a/cabal-install/src/Distribution/Client/Configure.hs
+++ b/cabal-install/src/Distribution/Client/Configure.hs
@@ -116,6 +116,9 @@ import Distribution.Simple.Utils as Utils
 import Distribution.System
   ( Platform
   )
+import Distribution.Types.DependencySatisfaction
+  ( DependencySatisfaction (..)
+  )
 import Distribution.Types.GivenComponent
   ( GivenComponent (..)
   )
@@ -555,7 +558,7 @@ configurePackage
       pkg = case finalizePD
         flags
         (enableStanzas stanzas)
-        (const True)
+        (const Satisfied)
         platform
         comp
         []
diff --git a/cabal-install/src/Distribution/Client/Dependency.hs b/cabal-install/src/Distribution/Client/Dependency.hs
index ae731cdc64b..d59bc611c44 100644
--- a/cabal-install/src/Distribution/Client/Dependency.hs
+++ b/cabal-install/src/Distribution/Client/Dependency.hs
@@ -127,6 +127,9 @@ import Distribution.System
   ( Platform
   )
 import Distribution.Types.Dependency
+import Distribution.Types.DependencySatisfaction
+  ( DependencySatisfaction (..)
+  )
 import Distribution.Verbosity
   ( normal
   )
@@ -1092,7 +1095,7 @@ configuredPackageProblems
         case finalizePD
           specifiedFlags
           compSpec
-          (const True)
+          (const Satisfied)
           platform
           cinfo
           []
diff --git a/cabal-install/src/Distribution/Client/GenBounds.hs b/cabal-install/src/Distribution/Client/GenBounds.hs
index 935db05fa43..2603a75d302 100644
--- a/cabal-install/src/Distribution/Client/GenBounds.hs
+++ b/cabal-install/src/Distribution/Client/GenBounds.hs
@@ -63,6 +63,9 @@ import Distribution.Types.ComponentRequestedSpec
   ( defaultComponentRequestedSpec
   )
 import Distribution.Types.Dependency
+import Distribution.Types.DependencySatisfaction
+  ( DependencySatisfaction (..)
+  )
 import Distribution.Utils.Path (relativeSymbolicPath)
 import Distribution.Version
   ( LowerBound (..)
@@ -134,7 +137,7 @@ genBounds verbosity packageDBs repoCtxt comp platform progdb globalFlags freezeF
         finalizePD
           mempty
           defaultComponentRequestedSpec
-          (const True)
+          (const Satisfied)
           platform
           cinfo
           []
diff --git a/cabal-install/src/Distribution/Client/HttpUtils.hs b/cabal-install/src/Distribution/Client/HttpUtils.hs
index 956241ab307..3cdadf9304c 100644
--- a/cabal-install/src/Distribution/Client/HttpUtils.hs
+++ b/cabal-install/src/Distribution/Client/HttpUtils.hs
@@ -467,7 +467,6 @@ curlTransport prog =
   where
     gethttp verbosity uri etag destPath reqHeaders = do
       withTempFile
-        (takeDirectory destPath)
         "curl-headers.txt"
         $ \tmpFile tmpHandle -> do
           hClose tmpHandle
@@ -675,10 +674,9 @@ wgetTransport prog =
 
     posthttpfile verbosity uri path auth =
       withTempFile
-        (takeDirectory path)
         (takeFileName path)
         $ \tmpFile tmpHandle ->
-          withTempFile (takeDirectory path) "response" $
+          withTempFile "response" $
             \responseFile responseHandle -> do
               hClose responseHandle
               (body, boundary) <- generateMultipartBody path
@@ -702,7 +700,7 @@ wgetTransport prog =
                 evaluate $ force (code, resp)
 
     puthttpfile verbosity uri path auth headers =
-      withTempFile (takeDirectory path) "response" $
+      withTempFile "response" $
         \responseFile responseHandle -> do
           hClose responseHandle
           let args =
@@ -824,7 +822,6 @@ powershellTransport prog =
 
     posthttpfile verbosity uri path auth =
       withTempFile
-        (takeDirectory path)
         (takeFileName path)
         $ \tmpFile tmpHandle -> do
           (body, boundary) <- generateMultipartBody path
diff --git a/cabal-install/src/Distribution/Client/Install.hs b/cabal-install/src/Distribution/Client/Install.hs
index 84a590e3c74..b6a8198ae5c 100644
--- a/cabal-install/src/Distribution/Client/Install.hs
+++ b/cabal-install/src/Distribution/Client/Install.hs
@@ -244,6 +244,9 @@ import Distribution.System
   , buildOS
   , buildPlatform
   )
+import Distribution.Types.DependencySatisfaction
+  ( DependencySatisfaction (..)
+  )
 import Distribution.Types.Flag
   ( FlagAssignment
   , PackageFlag (..)
@@ -1676,7 +1679,7 @@ installReadyPackage
       pkg = case finalizePD
         flags
         (enableStanzas stanzas)
-        (const True)
+        (const Satisfied)
         platform
         cinfo
         []
diff --git a/cabal-install/src/Distribution/Client/InstallSymlink.hs b/cabal-install/src/Distribution/Client/InstallSymlink.hs
index 7a470843779..46e1edaebef 100644
--- a/cabal-install/src/Distribution/Client/InstallSymlink.hs
+++ b/cabal-install/src/Distribution/Client/InstallSymlink.hs
@@ -74,6 +74,9 @@ import Distribution.Simple.Utils (info, withTempDirectory)
 import Distribution.System
   ( Platform
   )
+import Distribution.Types.DependencySatisfaction
+  ( DependencySatisfaction (..)
+  )
 import Distribution.Types.UnqualComponentName
 
 import System.Directory
@@ -205,7 +208,7 @@ symlinkBinaries
           case finalizePD
             flags
             (enableStanzas stanzas)
-            (const True)
+            (const Satisfied)
             platform
             cinfo
             []
diff --git a/cabal-install/src/Distribution/Client/ProjectBuilding/UnpackedPackage.hs b/cabal-install/src/Distribution/Client/ProjectBuilding/UnpackedPackage.hs
index f1486388b8c..9e3b91d1753 100644
--- a/cabal-install/src/Distribution/Client/ProjectBuilding/UnpackedPackage.hs
+++ b/cabal-install/src/Distribution/Client/ProjectBuilding/UnpackedPackage.hs
@@ -44,10 +44,14 @@ import Distribution.Client.FileMonitor
 import Distribution.Client.JobControl
 import Distribution.Client.Setup
   ( CommonSetupFlags
-  , filterCommonFlags
+  , filterBenchmarkFlags
+  , filterBuildFlags
   , filterConfigureFlags
+  , filterCopyFlags
   , filterHaddockArgs
   , filterHaddockFlags
+  , filterRegisterFlags
+  , filterReplFlags
   , filterTestFlags
   )
 import Distribution.Client.SetupWrapper
@@ -272,9 +276,7 @@ buildAndRegisterUnpackedPackage
         | otherwise = return ()
 
       mbWorkDir = useWorkingDir scriptOptions
-      commonFlags v =
-        flip filterCommonFlags v $
-          setupHsCommonFlags verbosity mbWorkDir builddir
+      commonFlags = setupHsCommonFlags verbosity mbWorkDir builddir
 
       configureCommand = Cabal.configureCommand defaultProgramDb
       configureFlags v =
@@ -284,19 +286,26 @@ buildAndRegisterUnpackedPackage
             plan
             rpkg
             pkgshared
-            (commonFlags v)
+            commonFlags
       configureArgs _ = setupHsConfigureArgs pkg
 
       buildCommand = Cabal.buildCommand defaultProgramDb
-      buildFlags v = setupHsBuildFlags comp_par_strat pkg pkgshared $ commonFlags v
+      buildFlags v =
+        flip filterBuildFlags v $
+          setupHsBuildFlags
+            comp_par_strat
+            pkg
+            pkgshared
+            commonFlags
       buildArgs _ = setupHsBuildArgs pkg
 
       copyFlags destdir v =
-        setupHsCopyFlags
-          pkg
-          pkgshared
-          (commonFlags v)
-          destdir
+        flip filterCopyFlags v $
+          setupHsCopyFlags
+            pkg
+            pkgshared
+            commonFlags
+            destdir
       -- In theory, we could want to copy less things than those that were
       -- built, but instead, we simply copy the targets that were built.
       copyArgs = buildArgs
@@ -306,23 +315,25 @@ buildAndRegisterUnpackedPackage
         flip filterTestFlags v $
           setupHsTestFlags
             pkg
-            (commonFlags v)
+            commonFlags
       testArgs _ = setupHsTestArgs pkg
 
       benchCommand = Cabal.benchmarkCommand
       benchFlags v =
-        setupHsBenchFlags
-          pkg
-          pkgshared
-          (commonFlags v)
+        flip filterBenchmarkFlags v $
+          setupHsBenchFlags
+            pkg
+            pkgshared
+            commonFlags
       benchArgs _ = setupHsBenchArgs pkg
 
       replCommand = Cabal.replCommand defaultProgramDb
       replFlags v =
-        setupHsReplFlags
-          pkg
-          pkgshared
-          (commonFlags v)
+        flip filterReplFlags v $
+          setupHsReplFlags
+            pkg
+            pkgshared
+            commonFlags
       replArgs _ = setupHsReplArgs pkg
 
       haddockCommand = Cabal.haddockCommand
@@ -332,7 +343,7 @@ buildAndRegisterUnpackedPackage
             pkg
             pkgshared
             buildTimeSettings
-            (commonFlags v)
+            commonFlags
       haddockArgs v =
         flip filterHaddockArgs v $
           setupHsHaddockArgs pkg
@@ -394,11 +405,12 @@ buildAndRegisterUnpackedPackage
           distTempDirectory
           $ \pkgConfDest -> do
             let registerFlags v =
-                  setupHsRegisterFlags
-                    pkg
-                    pkgshared
-                    (commonFlags v)
-                    pkgConfDest
+                  flip filterRegisterFlags v $
+                    setupHsRegisterFlags
+                      pkg
+                      pkgshared
+                      commonFlags
+                      pkgConfDest
             setup (Cabal.registerCommand) Cabal.registerCommonFlags (\v -> return (registerFlags v)) (const [])
 
       withLogging :: (Maybe Handle -> IO r) -> IO r
diff --git a/cabal-install/src/Distribution/Client/ProjectPlanning.hs b/cabal-install/src/Distribution/Client/ProjectPlanning.hs
index 50423b2d1df..93baa8bf78f 100644
--- a/cabal-install/src/Distribution/Client/ProjectPlanning.hs
+++ b/cabal-install/src/Distribution/Client/ProjectPlanning.hs
@@ -176,6 +176,9 @@ import Distribution.System
 import Distribution.Types.AnnotatedId
 import Distribution.Types.ComponentInclude
 import Distribution.Types.ComponentName
+import Distribution.Types.DependencySatisfaction
+  ( DependencySatisfaction (..)
+  )
 import Distribution.Types.DumpBuildInfo
 import Distribution.Types.GivenComponent
 import Distribution.Types.LibraryName
@@ -2130,7 +2133,7 @@ elaborateInstallPlan
             elabPkgDescription = case PD.finalizePD
               flags
               elabEnabledSpec
-              (const True)
+              (const Satisfied)
               platform
               (compilerInfo compiler)
               []
diff --git a/cabal-install/src/Distribution/Client/Setup.hs b/cabal-install/src/Distribution/Client/Setup.hs
index 78e864d1a65..aebba9462c0 100644
--- a/cabal-install/src/Distribution/Client/Setup.hs
+++ b/cabal-install/src/Distribution/Client/Setup.hs
@@ -35,12 +35,15 @@ module Distribution.Client.Setup
   , defaultConfigExFlags
   , buildCommand
   , BuildFlags (..)
+  , filterBuildFlags
   , filterTestFlags
   , replCommand
+  , filterReplFlags
   , testCommand
   , benchmarkCommand
   , testOptions
   , benchmarkOptions
+  , filterBenchmarkFlags
   , configureExOptions
   , reconfigureCommand
   , installCommand
@@ -87,7 +90,9 @@ module Distribution.Client.Setup
   , haddockCommand
   , cleanCommand
   , copyCommand
+  , filterCopyFlags
   , registerCommand
+  , filterRegisterFlags
   , liftOptions
   , yesNoOpt
   ) where
@@ -183,7 +188,7 @@ import Distribution.Simple.InstallDirs
   )
 import Distribution.Simple.Program (ProgramDb, defaultProgramDb)
 import Distribution.Simple.Setup
-  ( BenchmarkFlags
+  ( BenchmarkFlags (benchmarkCommonFlags)
   , BooleanFlag (..)
   , BuildFlags (..)
   , CleanFlags (..)
@@ -192,7 +197,7 @@ import Distribution.Simple.Setup
   , CopyFlags (..)
   , HaddockFlags (..)
   , RegisterFlags (..)
-  , ReplFlags
+  , ReplFlags (..)
   , TestFlags
   , boolOpt
   , boolOpt'
@@ -1144,6 +1149,21 @@ buildCommand =
   where
     parent = Cabal.buildCommand defaultProgramDb
 
+-- | Given some 'BuildFlags' for the version of @Cabal@ that
+-- @cabal-install@ was built with, and a target older 'Version' of
+-- @Cabal@ that we want to pass these flags to, convert the
+-- flags into a form that will be accepted by the older
+-- @Setup@ script.  Generally speaking, this just means filtering
+-- out flags that the old @Cabal@ library doesn't understand, but
+-- in some cases it may also mean "emulating" a feature using
+-- some more legacy flags.
+filterBuildFlags :: BuildFlags -> Version -> BuildFlags
+filterBuildFlags flags cabalLibVersion =
+  flags
+    { buildCommonFlags =
+        filterCommonFlags (buildCommonFlags flags) cabalLibVersion
+    }
+
 -- ------------------------------------------------------------
 
 -- * Test flags
@@ -1236,6 +1256,21 @@ replCommand =
   where
     parent = Cabal.replCommand defaultProgramDb
 
+-- | Given some 'ReplFlags' for the version of @Cabal@ that
+-- @cabal-install@ was built with, and a target older 'Version' of
+-- @Cabal@ that we want to pass these flags to, convert the
+-- flags into a form that will be accepted by the older
+-- @Setup@ script.  Generally speaking, this just means filtering
+-- out flags that the old @Cabal@ library doesn't understand, but
+-- in some cases it may also mean "emulating" a feature using
+-- some more legacy flags.
+filterReplFlags :: ReplFlags -> Version -> ReplFlags
+filterReplFlags flags cabalLibVersion =
+  flags
+    { replCommonFlags =
+        filterCommonFlags (replCommonFlags flags) cabalLibVersion
+    }
+
 -- ------------------------------------------------------------
 
 -- * Test command
@@ -1331,6 +1366,21 @@ benchmarkCommand =
     parent = Cabal.benchmarkCommand
     progDb = defaultProgramDb
 
+-- | Given some 'BenchmarkFlags' for the version of @Cabal@ that
+-- @cabal-install@ was built with, and a target older 'Version' of
+-- @Cabal@ that we want to pass these flags to, convert the
+-- flags into a form that will be accepted by the older
+-- @Setup@ script.  Generally speaking, this just means filtering
+-- out flags that the old @Cabal@ library doesn't understand, but
+-- in some cases it may also mean "emulating" a feature using
+-- some more legacy flags.
+filterBenchmarkFlags :: BenchmarkFlags -> Version -> BenchmarkFlags
+filterBenchmarkFlags flags cabalLibVersion =
+  flags
+    { benchmarkCommonFlags =
+        filterCommonFlags (benchmarkCommonFlags flags) cabalLibVersion
+    }
+
 -- ------------------------------------------------------------
 
 -- * Fetch command
@@ -2404,21 +2454,25 @@ filterHaddockArgs args cabalLibVersion
     -- Cabal < 2.3 doesn't know about per-component haddock
     args_2_3_0 = []
 
+-- | Given some 'HaddockFlags' for the version of @Cabal@ that
+-- @cabal-install@ was built with, and a target older 'Version' of
+-- @Cabal@ that we want to pass these flags to, convert the
+-- flags into a form that will be accepted by the older
+-- @Setup@ script.  Generally speaking, this just means filtering
+-- out flags that the old @Cabal@ library doesn't understand, but
+-- in some cases it may also mean "emulating" a feature using
+-- some more legacy flags.
 filterHaddockFlags :: HaddockFlags -> Version -> HaddockFlags
-filterHaddockFlags flags cabalLibVersion =
-  let flags' = filterHaddockFlags' flags cabalLibVersion
-   in flags'
-        { haddockCommonFlags =
-            filterCommonFlags (haddockCommonFlags flags') cabalLibVersion
-        }
-
-filterHaddockFlags' :: HaddockFlags -> Version -> HaddockFlags
-filterHaddockFlags' flags cabalLibVersion
+filterHaddockFlags flags cabalLibVersion
   | cabalLibVersion >= mkVersion [2, 3, 0] = flags_latest
   | cabalLibVersion < mkVersion [2, 3, 0] = flags_2_3_0
   | otherwise = flags_latest
   where
-    flags_latest = flags
+    flags_latest =
+      flags
+        { haddockCommonFlags =
+            filterCommonFlags (haddockCommonFlags flags) cabalLibVersion
+        }
 
     flags_2_3_0 =
       flags_latest
@@ -2490,6 +2544,9 @@ testOptions showOrParseArgs =
       | "test-" `isPrefixOf` name = name
       | otherwise = "test-" ++ name
 
+-- | Options for the @bench@ command.
+--
+-- Not to be confused with the @benchmarkOptions@ field of the `BenchmarkFlags` record!
 benchmarkOptions :: ShowOrParseArgs -> [OptionField BenchmarkFlags]
 benchmarkOptions showOrParseArgs =
   [ opt
@@ -3317,6 +3374,35 @@ registerCommand =
     { commandUsage = \pname -> "Usage: " ++ pname ++ " v1-register [FLAGS]\n"
     }
 
+-- | Given some 'RegisterFlags' for the version of @Cabal@ that
+-- @cabal-install@ was built with, and a target older 'Version' of
+-- @Cabal@ that we want to pass these flags to, convert the
+-- flags into a form that will be accepted by the older
+-- @Setup@ script.  Generally speaking, this just means filtering
+-- out flags that the old @Cabal@ library doesn't understand, but
+-- in some cases it may also mean "emulating" a feature using
+-- some more legacy flags.
+filterRegisterFlags :: RegisterFlags -> Version -> RegisterFlags
+filterRegisterFlags flags cabalLibVersion =
+  flags
+    { registerCommonFlags =
+        filterCommonFlags (registerCommonFlags flags) cabalLibVersion
+    }
+
+-- | Given some 'CopyFlags' for the version of @Cabal@ that
+-- @cabal-install@ was built with, and a target older 'Version' of
+-- @Cabal@ that we want to pass these flags to, convert the
+-- flags into a form that will be accepted by the older
+-- @Setup@ script.  Generally speaking, this just means filtering
+-- out flags that the old @Cabal@ library doesn't understand, but
+-- in some cases it may also mean "emulating" a feature using
+-- some more legacy flags.
+filterCopyFlags :: CopyFlags -> Version -> CopyFlags
+filterCopyFlags flags cabalLibVersion =
+  flags
+    { copyCommonFlags = filterCommonFlags (copyCommonFlags flags) cabalLibVersion
+    }
+
 -- ------------------------------------------------------------
 
 -- * ActAsSetup flags
diff --git a/cabal-install/tests/IntegrationTests2.hs b/cabal-install/tests/IntegrationTests2.hs
index e6373cd18b8..22c7da0c37f 100644
--- a/cabal-install/tests/IntegrationTests2.hs
+++ b/cabal-install/tests/IntegrationTests2.hs
@@ -103,7 +103,9 @@ main = do
   removeDirectoryRecursive configDir <|> return ()
   createDirectoryIfMissing True configDir
   -- sigh
-  callProcess "cabal" ["user-config", "init", "-f"]
+  -- NOTE: This is running the `cabal` from the user environment, which is
+  -- generally not the `cabal` being tested!
+  callProcess "cabal" ["-v0", "user-config", "init", "-f"]
   callProcess "cabal" ["update"]
   defaultMainWithIngredients
     (defaultIngredients ++ [includingOptions projectConfigOptionDescriptions])
@@ -1982,230 +1984,272 @@ testNixFlags = do
 -- Tests whether config options are commented or not
 testConfigOptionComments :: Assertion
 testConfigOptionComments = do
-  _ <- createDefaultConfigFile verbosity [] (basedir </> "config" </> "default-config")
-  defaultConfigFile <- readFile (basedir </> "config" </> "default-config")
-
-  "  url" @=? findLineWith False "url" defaultConfigFile
-  "  -- secure" @=? findLineWith True "secure" defaultConfigFile
-  "  -- root-keys" @=? findLineWith True "root-keys" defaultConfigFile
-  "  -- key-threshold" @=? findLineWith True "key-threshold" defaultConfigFile
-
-  "-- ignore-expiry" @=? findLineWith True "ignore-expiry" defaultConfigFile
-  "-- http-transport" @=? findLineWith True "http-transport" defaultConfigFile
-  "-- nix" @=? findLineWith True "nix" defaultConfigFile
-  "-- store-dir" @=? findLineWith True "store-dir" defaultConfigFile
-  "-- active-repositories" @=? findLineWith True "active-repositories" defaultConfigFile
-  "-- local-no-index-repo" @=? findLineWith True "local-no-index-repo" defaultConfigFile
-  "remote-repo-cache"  @=? findLineWith False "remote-repo-cache" defaultConfigFile
-  "-- logs-dir"  @=? findLineWith True "logs-dir" defaultConfigFile
-  "-- default-user-config" @=? findLineWith True "default-user-config" defaultConfigFile
-  "-- verbose" @=? findLineWith True "verbose" defaultConfigFile
-  "-- compiler" @=? findLineWith True "compiler" defaultConfigFile
-  "-- cabal-file" @=? findLineWith True "cabal-file" defaultConfigFile
-  "-- with-compiler" @=? findLineWith True "with-compiler" defaultConfigFile
-  "-- with-hc-pkg" @=? findLineWith True "with-hc-pkg" defaultConfigFile
-  "-- program-prefix" @=? findLineWith True "program-prefix" defaultConfigFile
-  "-- program-suffix" @=? findLineWith True "program-suffix" defaultConfigFile
-  "-- library-vanilla" @=? findLineWith True "library-vanilla" defaultConfigFile
-  "-- library-profiling" @=? findLineWith True "library-profiling" defaultConfigFile
-  "-- shared" @=? findLineWith True "shared" defaultConfigFile
-  "-- static" @=? findLineWith True "static" defaultConfigFile
-  "-- executable-dynamic" @=? findLineWith True "executable-dynamic" defaultConfigFile
-  "-- executable-static" @=? findLineWith True "executable-static" defaultConfigFile
-  "-- profiling" @=? findLineWith True "profiling" defaultConfigFile
-  "-- executable-profiling" @=? findLineWith True "executable-profiling" defaultConfigFile
-  "-- profiling-detail" @=? findLineWith True "profiling-detail" defaultConfigFile
-  "-- library-profiling-detail" @=? findLineWith True "library-profiling-detail" defaultConfigFile
-  "-- optimization" @=? findLineWith True "optimization" defaultConfigFile
-  "-- debug-info" @=? findLineWith True "debug-info" defaultConfigFile
-  "-- build-info" @=? findLineWith True "build-info" defaultConfigFile
-  "-- library-for-ghci" @=? findLineWith True "library-for-ghci" defaultConfigFile
-  "-- split-sections" @=? findLineWith True "split-sections" defaultConfigFile
-  "-- split-objs" @=? findLineWith True "split-objs" defaultConfigFile
-  "-- executable-stripping" @=? findLineWith True "executable-stripping" defaultConfigFile
-  "-- library-stripping" @=? findLineWith True "library-stripping" defaultConfigFile
-  "-- configure-option" @=? findLineWith True "configure-option" defaultConfigFile
-  "-- user-install"  @=? findLineWith True "user-install" defaultConfigFile
-  "-- package-db"  @=? findLineWith True "package-db" defaultConfigFile
-  "-- flags" @=? findLineWith True "flags" defaultConfigFile
-  "-- extra-include-dirs" @=? findLineWith True "extra-include-dirs" defaultConfigFile
-  "-- deterministic" @=? findLineWith True "deterministic" defaultConfigFile
-  "-- cid" @=? findLineWith True "cid" defaultConfigFile
-  "-- extra-lib-dirs" @=? findLineWith True "extra-lib-dirs" defaultConfigFile
-  "-- extra-lib-dirs-static" @=? findLineWith True "extra-lib-dirs-static" defaultConfigFile
-  "-- extra-framework-dirs" @=? findLineWith True "extra-framework-dirs" defaultConfigFile
-  "-- extra-prog-path"  @=? findLineWith False "extra-prog-path" defaultConfigFile
-  "-- instantiate-with" @=? findLineWith True "instantiate-with" defaultConfigFile
-  "-- tests" @=? findLineWith True "tests" defaultConfigFile
-  "-- coverage" @=? findLineWith True "coverage" defaultConfigFile
-  "-- library-coverage" @=? findLineWith True "library-coverage" defaultConfigFile
-  "-- exact-configuration" @=? findLineWith True "exact-configuration" defaultConfigFile
-  "-- benchmarks" @=? findLineWith True "benchmarks" defaultConfigFile
-  "-- relocatable"  @=? findLineWith True "relocatable" defaultConfigFile
-  "-- response-files" @=? findLineWith True "response-files" defaultConfigFile
-  "-- allow-depending-on-private-libs" @=? findLineWith True "allow-depending-on-private-libs" defaultConfigFile
-  "-- cabal-lib-version" @=? findLineWith True "cabal-lib-version" defaultConfigFile
-  "-- append" @=? findLineWith True "append" defaultConfigFile
-  "-- backup" @=? findLineWith True "backup" defaultConfigFile
-  "-- constraint" @=? findLineWith True "constraint" defaultConfigFile
-  "-- preference" @=? findLineWith True "preference" defaultConfigFile
-  "-- solver"  @=? findLineWith True "solver" defaultConfigFile
-  "-- allow-older"  @=? findLineWith True "allow-older" defaultConfigFile
-  "-- allow-newer"  @=? findLineWith True "allow-newer" defaultConfigFile
-  "-- write-ghc-environment-files" @=? findLineWith True "write-ghc-environment-files" defaultConfigFile
-  "-- documentation"  @=? findLineWith True "documentation" defaultConfigFile
-  "-- doc-index-file"  @=? findLineWith True "doc-index-file" defaultConfigFile
-  "-- only-download"  @=? findLineWith True "only-download" defaultConfigFile
-  "-- target-package-db" @=? findLineWith True "target-package-db" defaultConfigFile
-  "-- max-backjumps"  @=? findLineWith True "max-backjumps" defaultConfigFile
-  "-- reorder-goals"  @=? findLineWith True "reorder-goals" defaultConfigFile
-  "-- count-conflicts"  @=? findLineWith True "count-conflicts" defaultConfigFile
-  "-- fine-grained-conflicts"  @=? findLineWith True "fine-grained-conflicts" defaultConfigFile
-  "-- minimize-conflict-set"  @=? findLineWith True "minimize-conflict-set" defaultConfigFile
-  "-- independent-goals"  @=? findLineWith True "independent-goals" defaultConfigFile
-  "-- prefer-oldest"  @=? findLineWith True "prefer-oldest" defaultConfigFile
-  "-- shadow-installed-packages"  @=? findLineWith True "shadow-installed-packages" defaultConfigFile
-  "-- strong-flags"  @=? findLineWith True "strong-flags" defaultConfigFile
-  "-- allow-boot-library-installs"  @=? findLineWith True "allow-boot-library-installs" defaultConfigFile
-  "-- reject-unconstrained-dependencies"  @=? findLineWith True "reject-unconstrained-dependencies" defaultConfigFile
-  "-- reinstall"  @=? findLineWith True "reinstall" defaultConfigFile
-  "-- avoid-reinstalls"  @=? findLineWith True "avoid-reinstalls" defaultConfigFile
-  "-- force-reinstalls"  @=? findLineWith True "force-reinstalls" defaultConfigFile
-  "-- upgrade-dependencies"  @=? findLineWith True "upgrade-dependencies" defaultConfigFile
-  "-- index-state" @=? findLineWith True "index-state" defaultConfigFile
-  "-- root-cmd" @=? findLineWith True "root-cmd" defaultConfigFile
-  "-- symlink-bindir" @=? findLineWith True "symlink-bindir" defaultConfigFile
-  "build-summary"  @=? findLineWith False "build-summary" defaultConfigFile
-  "-- build-log" @=? findLineWith True "build-log" defaultConfigFile
-  "remote-build-reporting"  @=? findLineWith False "remote-build-reporting" defaultConfigFile
-  "-- report-planning-failure"  @=? findLineWith True "report-planning-failure" defaultConfigFile
-  "-- per-component"  @=? findLineWith True "per-component" defaultConfigFile
-  "-- run-tests" @=? findLineWith True "run-tests" defaultConfigFile
-  "jobs"  @=? findLineWith False "jobs" defaultConfigFile
-  "-- keep-going"  @=? findLineWith True "keep-going" defaultConfigFile
-  "-- offline"  @=? findLineWith True "offline" defaultConfigFile
-  "-- lib" @=? findLineWith True "lib" defaultConfigFile
-  "-- package-env" @=? findLineWith True "package-env" defaultConfigFile
-  "-- overwrite-policy" @=? findLineWith True "overwrite-policy" defaultConfigFile
-  "-- install-method" @=? findLineWith True "install-method" defaultConfigFile
-  "installdir"  @=? findLineWith False "installdir" defaultConfigFile
-  "-- token" @=? findLineWith True "token" defaultConfigFile
-  "-- username" @=? findLineWith True "username" defaultConfigFile
-  "-- password" @=? findLineWith True "password" defaultConfigFile
-  "-- password-command" @=? findLineWith True "password-command" defaultConfigFile
-  "-- builddir" @=? findLineWith True "builddir" defaultConfigFile
-
-  "  -- keep-temp-files" @=? findLineWith True "keep-temp-files" defaultConfigFile
-  "  -- hoogle" @=? findLineWith True "hoogle" defaultConfigFile
-  "  -- html" @=? findLineWith True "html" defaultConfigFile
-  "  -- html-location" @=? findLineWith True "html-location" defaultConfigFile
-  "  -- executables" @=? findLineWith True "executables" defaultConfigFile
-  "  -- foreign-libraries" @=? findLineWith True "foreign-libraries" defaultConfigFile
-  "  -- all" @=? findLineWith True "all" defaultConfigFile
-  "  -- internal" @=? findLineWith True "internal" defaultConfigFile
-  "  -- css" @=? findLineWith True "css" defaultConfigFile
-  "  -- hyperlink-source" @=? findLineWith True "hyperlink-source" defaultConfigFile
-  "  -- quickjump" @=? findLineWith True "quickjump" defaultConfigFile
-  "  -- hscolour-css" @=? findLineWith True "hscolour-css" defaultConfigFile
-  "  -- contents-location" @=? findLineWith True "contents-location" defaultConfigFile
-  "  -- index-location" @=? findLineWith True "index-location" defaultConfigFile
-  "  -- base-url" @=? findLineWith True "base-url" defaultConfigFile
-  "  -- resources-dir" @=? findLineWith True "resources-dir" defaultConfigFile
-  "  -- output-dir" @=? findLineWith True "output-dir" defaultConfigFile
-  "  -- use-unicode" @=? findLineWith True "use-unicode" defaultConfigFile
-
-  "  -- interactive" @=? findLineWith True "interactive" defaultConfigFile
-  "  -- quiet" @=? findLineWith True "quiet" defaultConfigFile
-  "  -- no-comments" @=? findLineWith True "no-comments" defaultConfigFile
-  "  -- minimal" @=? findLineWith True "minimal" defaultConfigFile
-  "  -- cabal-version" @=? findLineWith True "cabal-version" defaultConfigFile
-  "  -- license" @=? findLineWith True "license" defaultConfigFile
-  "  -- extra-doc-file" @=? findLineWith True "extra-doc-file" defaultConfigFile
-  "  -- test-dir" @=? findLineWith True "test-dir" defaultConfigFile
-  "  -- simple" @=? findLineWith True "simple" defaultConfigFile
-  "  -- language" @=? findLineWith True "language" defaultConfigFile
-  "  -- application-dir" @=? findLineWith True "application-dir" defaultConfigFile
-  "  -- source-dir" @=? findLineWith True "source-dir" defaultConfigFile
-
-  "  -- prefix"  @=? findLineWith True "prefix" defaultConfigFile
-  "  -- bindir"@=? findLineWith True "bindir" defaultConfigFile
-  "  -- libdir" @=? findLineWith True "libdir" defaultConfigFile
-  "  -- libsubdir" @=? findLineWith True "libsubdir" defaultConfigFile
-  "  -- dynlibdir" @=? findLineWith True "dynlibdir" defaultConfigFile
-  "  -- libexecdir" @=? findLineWith True "libexecdir" defaultConfigFile
-  "  -- libexecsubdir" @=? findLineWith True "libexecsubdir" defaultConfigFile
-  "  -- datadir" @=? findLineWith True "datadir" defaultConfigFile
-  "  -- datasubdir" @=? findLineWith True "datasubdir" defaultConfigFile
-  "  -- docdir" @=? findLineWith True "docdir" defaultConfigFile
-  "  -- htmldir" @=? findLineWith True "htmldir" defaultConfigFile
-  "  -- haddockdir" @=? findLineWith True "haddockdir" defaultConfigFile
-  "  -- sysconfdir" @=? findLineWith True "sysconfdir" defaultConfigFile
-
-  "  -- alex-location" @=? findLineWith True "alex-location" defaultConfigFile
-  "  -- ar-location" @=? findLineWith True "ar-location" defaultConfigFile
-  "  -- c2hs-location" @=? findLineWith True "c2hs-location" defaultConfigFile
-  "  -- cpphs-location" @=? findLineWith True "cpphs-location" defaultConfigFile
-  "  -- doctest-location" @=? findLineWith True "doctest-location" defaultConfigFile
-  "  -- gcc-location" @=? findLineWith True "gcc-location" defaultConfigFile
-  "  -- ghc-location" @=? findLineWith True "ghc-location" defaultConfigFile
-  "  -- ghc-pkg-location" @=? findLineWith True "ghc-pkg-location" defaultConfigFile
-  "  -- ghcjs-location" @=? findLineWith True "ghcjs-location" defaultConfigFile
-  "  -- ghcjs-pkg-location" @=? findLineWith True "ghcjs-pkg-location" defaultConfigFile
-  "  -- greencard-location" @=? findLineWith True "greencard-location" defaultConfigFile
-  "  -- haddock-location" @=? findLineWith True "haddock-location" defaultConfigFile
-  "  -- happy-location" @=? findLineWith True "happy-location" defaultConfigFile
-  "  -- haskell-suite-location" @=? findLineWith True "haskell-suite-location" defaultConfigFile
-  "  -- haskell-suite-pkg-location" @=? findLineWith True "haskell-suite-pkg-location" defaultConfigFile
-  "  -- hmake-location" @=? findLineWith True "hmake-location" defaultConfigFile
-  "  -- hpc-location" @=? findLineWith True "hpc-location" defaultConfigFile
-  "  -- hscolour-location" @=? findLineWith True "hscolour-location" defaultConfigFile
-  "  -- jhc-location" @=? findLineWith True "jhc-location" defaultConfigFile
-  "  -- ld-location" @=? findLineWith True "ld-location" defaultConfigFile
-  "  -- pkg-config-location" @=? findLineWith True "pkg-config-location" defaultConfigFile
-  "  -- runghc-location" @=? findLineWith True "runghc-location" defaultConfigFile
-  "  -- strip-location" @=? findLineWith True "strip-location" defaultConfigFile
-  "  -- tar-location" @=? findLineWith True "tar-location" defaultConfigFile
-  "  -- uhc-location" @=? findLineWith True "uhc-location" defaultConfigFile
-
-  "  -- alex-options" @=? findLineWith True "alex-options" defaultConfigFile
-  "  -- ar-options" @=? findLineWith True "ar-options" defaultConfigFile
-  "  -- c2hs-options" @=? findLineWith True "c2hs-options" defaultConfigFile
-  "  -- cpphs-options" @=? findLineWith True "cpphs-options" defaultConfigFile
-  "  -- doctest-options" @=? findLineWith True "doctest-options" defaultConfigFile
-  "  -- gcc-options" @=? findLineWith True "gcc-options" defaultConfigFile
-  "  -- ghc-options" @=? findLineWith True "ghc-options" defaultConfigFile
-  "  -- ghc-pkg-options" @=? findLineWith True "ghc-pkg-options" defaultConfigFile
-  "  -- ghcjs-options" @=? findLineWith True "ghcjs-options" defaultConfigFile
-  "  -- ghcjs-pkg-options" @=? findLineWith True "ghcjs-pkg-options" defaultConfigFile
-  "  -- greencard-options" @=? findLineWith True "greencard-options" defaultConfigFile
-  "  -- haddock-options" @=? findLineWith True "haddock-options" defaultConfigFile
-  "  -- happy-options" @=? findLineWith True "happy-options" defaultConfigFile
-  "  -- haskell-suite-options" @=? findLineWith True "haskell-suite-options" defaultConfigFile
-  "  -- haskell-suite-pkg-options" @=? findLineWith True "haskell-suite-pkg-options" defaultConfigFile
-  "  -- hmake-options" @=? findLineWith True "hmake-options" defaultConfigFile
-  "  -- hpc-options" @=? findLineWith True "hpc-options" defaultConfigFile
-  "  -- hsc2hs-options" @=? findLineWith True "hsc2hs-options" defaultConfigFile
-  "  -- hscolour-options" @=? findLineWith True "hscolour-options" defaultConfigFile
-  "  -- jhc-options" @=? findLineWith True "jhc-options" defaultConfigFile
-  "  -- ld-options" @=? findLineWith True "ld-options" defaultConfigFile
-  "  -- pkg-config-options" @=? findLineWith True "pkg-config-options" defaultConfigFile
-  "  -- runghc-options" @=? findLineWith True "runghc-options" defaultConfigFile
-  "  -- strip-options" @=? findLineWith True "strip-options" defaultConfigFile
-  "  -- tar-options" @=? findLineWith True "tar-options" defaultConfigFile
-  "  -- uhc-options" @=? findLineWith True "uhc-options" defaultConfigFile
-  where
-    -- | Find lines containing a target string.
+  let
+    -- | Find the first line containing a target setting name.
+    --
+    -- If `isComment` is set, only comment lines will be found.
     findLineWith :: Bool -> String -> String -> String
     findLineWith isComment target text =
       case findLinesWith isComment target text of
         [] -> text
-        (l : _) -> removeCommentValue l
+        (l : _) -> removeColonAndAfter l
+
+    -- | Find lines containing a target setting name.
     findLinesWith :: Bool -> String -> String -> [String]
     findLinesWith isComment target
-      | isComment = filter (isInfixOf (" " ++ target ++ ":")) . lines
+      | isComment = filter (isInfixOf ("-- " ++ target ++ ":")) . lines
       | otherwise = filter (isInfixOf (target ++ ":")) . lines
-    removeCommentValue :: String -> String
-    removeCommentValue = takeWhile (/= ':')
+
+    -- | Transform @-- puppy: doggy@ into @-- puppy@.
+    removeColonAndAfter :: String -> String
+    removeColonAndAfter = takeWhile (/= ':')
+
+  cwd <- getCurrentDirectory
+  let configFile = cwd </> basedir </> "config" </> "default-config"
+  _ <- createDefaultConfigFile verbosity [] configFile
+  defaultConfigFile <- readFile configFile
+
+  let
+    -- TODO: These assertions are fairly weak. Potential improvements:
+    --
+    -- - Include the section name in the assertion, so that (e.g.) a
+    --   `keep-temp-files` setting in the `haddock` section won't be confused
+    --   with a `keep-temp-files` setting in the `init` section.
+    --
+    -- - Check all matching lines to confirm that settings are not listed
+    --   multiple times. For example, `cabal-file` is listed twice right now,
+    --   once under the `haddock` settings!
+    --
+    -- - Consume the file as we go, ensuring that the settings are in a given
+    --   order.
+    --
+    -- - Check the generated config file into Git (replacing e.g. `$HOME` with
+    --   a sentinel value) so changes show up in PR diffs.
+    assertHasLine' :: Bool -> String -> String -> Assertion
+    assertHasLine' isComment expected settingName =
+      let actual = findLineWith isComment settingName defaultConfigFile
+          messagePrefix =
+            "Did not find expected line for setting "
+            <> show settingName
+            <> " in configuration file "
+            <> configFile
+      in assertEqual messagePrefix expected actual
+
+    assertHasLine :: String -> String -> Assertion
+    assertHasLine = assertHasLine' False
+
+    assertHasCommentLine :: String -> String -> Assertion
+    assertHasCommentLine = assertHasLine' True
+
+
+  "  url" `assertHasLine` "url"
+  "  -- secure" `assertHasCommentLine` "secure"
+  "  -- root-keys" `assertHasCommentLine` "root-keys"
+  "  -- key-threshold" `assertHasCommentLine` "key-threshold"
+
+  "-- ignore-expiry" `assertHasCommentLine` "ignore-expiry"
+  "-- http-transport" `assertHasCommentLine` "http-transport"
+  "-- nix" `assertHasCommentLine` "nix"
+  "-- store-dir" `assertHasCommentLine` "store-dir"
+  "-- active-repositories" `assertHasCommentLine` "active-repositories"
+  "-- local-no-index-repo" `assertHasCommentLine` "local-no-index-repo"
+  "remote-repo-cache" `assertHasLine` "remote-repo-cache"
+  "-- logs-dir" `assertHasCommentLine` "logs-dir"
+  "-- default-user-config" `assertHasCommentLine` "default-user-config"
+  "-- verbose" `assertHasCommentLine` "verbose"
+  "-- compiler" `assertHasCommentLine` "compiler"
+  "-- cabal-file" `assertHasCommentLine` "cabal-file"
+  "-- with-compiler" `assertHasCommentLine` "with-compiler"
+  "-- with-hc-pkg" `assertHasCommentLine` "with-hc-pkg"
+  "-- program-prefix" `assertHasCommentLine` "program-prefix"
+  "-- program-suffix" `assertHasCommentLine` "program-suffix"
+  "-- library-vanilla" `assertHasCommentLine` "library-vanilla"
+  "-- library-profiling" `assertHasCommentLine` "library-profiling"
+  "-- shared" `assertHasCommentLine` "shared"
+  "-- static" `assertHasCommentLine` "static"
+  "-- executable-dynamic" `assertHasCommentLine` "executable-dynamic"
+  "-- executable-static" `assertHasCommentLine` "executable-static"
+  "-- profiling" `assertHasCommentLine` "profiling"
+  "-- executable-profiling" `assertHasCommentLine` "executable-profiling"
+  "-- profiling-detail" `assertHasCommentLine` "profiling-detail"
+  "-- library-profiling-detail" `assertHasCommentLine` "library-profiling-detail"
+  "-- optimization" `assertHasCommentLine` "optimization"
+  "-- debug-info" `assertHasCommentLine` "debug-info"
+  "-- build-info" `assertHasCommentLine` "build-info"
+  "-- library-for-ghci" `assertHasCommentLine` "library-for-ghci"
+  "-- split-sections" `assertHasCommentLine` "split-sections"
+  "-- split-objs" `assertHasCommentLine` "split-objs"
+  "-- executable-stripping" `assertHasCommentLine` "executable-stripping"
+  "-- library-stripping" `assertHasCommentLine` "library-stripping"
+  "-- configure-option" `assertHasCommentLine` "configure-option"
+  "-- user-install" `assertHasCommentLine` "user-install"
+  "-- package-db" `assertHasCommentLine` "package-db"
+  "-- flags" `assertHasCommentLine` "flags"
+  "-- extra-include-dirs" `assertHasCommentLine` "extra-include-dirs"
+  "-- deterministic" `assertHasCommentLine` "deterministic"
+  "-- cid" `assertHasCommentLine` "cid"
+  "-- extra-lib-dirs" `assertHasCommentLine` "extra-lib-dirs"
+  "-- extra-lib-dirs-static" `assertHasCommentLine` "extra-lib-dirs-static"
+  "-- extra-framework-dirs" `assertHasCommentLine` "extra-framework-dirs"
+  "-- extra-prog-path" `assertHasLine` "extra-prog-path"
+  "-- instantiate-with" `assertHasCommentLine` "instantiate-with"
+  "-- tests" `assertHasCommentLine` "tests"
+  "-- coverage" `assertHasCommentLine` "coverage"
+  "-- library-coverage" `assertHasCommentLine` "library-coverage"
+  "-- exact-configuration" `assertHasCommentLine` "exact-configuration"
+  "-- benchmarks" `assertHasCommentLine` "benchmarks"
+  "-- relocatable" `assertHasCommentLine` "relocatable"
+  "-- response-files" `assertHasCommentLine` "response-files"
+  "-- allow-depending-on-private-libs" `assertHasCommentLine` "allow-depending-on-private-libs"
+  "-- cabal-lib-version" `assertHasCommentLine` "cabal-lib-version"
+  "-- append" `assertHasCommentLine` "append"
+  "-- backup" `assertHasCommentLine` "backup"
+  "-- constraint" `assertHasCommentLine` "constraint"
+  "-- preference" `assertHasCommentLine` "preference"
+  "-- solver" `assertHasCommentLine` "solver"
+  "-- allow-older" `assertHasCommentLine` "allow-older"
+  "-- allow-newer" `assertHasCommentLine` "allow-newer"
+  "-- write-ghc-environment-files" `assertHasCommentLine` "write-ghc-environment-files"
+  "-- documentation" `assertHasCommentLine` "documentation"
+  "-- doc-index-file" `assertHasCommentLine` "doc-index-file"
+  "-- only-download" `assertHasCommentLine` "only-download"
+  "-- target-package-db" `assertHasCommentLine` "target-package-db"
+  "-- max-backjumps" `assertHasCommentLine` "max-backjumps"
+  "-- reorder-goals" `assertHasCommentLine` "reorder-goals"
+  "-- count-conflicts" `assertHasCommentLine` "count-conflicts"
+  "-- fine-grained-conflicts" `assertHasCommentLine` "fine-grained-conflicts"
+  "-- minimize-conflict-set" `assertHasCommentLine` "minimize-conflict-set"
+  "-- independent-goals" `assertHasCommentLine` "independent-goals"
+  "-- prefer-oldest" `assertHasCommentLine` "prefer-oldest"
+  "-- shadow-installed-packages" `assertHasCommentLine` "shadow-installed-packages"
+  "-- strong-flags" `assertHasCommentLine` "strong-flags"
+  "-- allow-boot-library-installs" `assertHasCommentLine` "allow-boot-library-installs"
+  "-- reject-unconstrained-dependencies" `assertHasCommentLine` "reject-unconstrained-dependencies"
+  "-- reinstall" `assertHasCommentLine` "reinstall"
+  "-- avoid-reinstalls" `assertHasCommentLine` "avoid-reinstalls"
+  "-- force-reinstalls" `assertHasCommentLine` "force-reinstalls"
+  "-- upgrade-dependencies" `assertHasCommentLine` "upgrade-dependencies"
+  "-- index-state" `assertHasCommentLine` "index-state"
+  "-- root-cmd" `assertHasCommentLine` "root-cmd"
+  "-- symlink-bindir" `assertHasCommentLine` "symlink-bindir"
+  "build-summary" `assertHasLine` "build-summary"
+  "-- build-log" `assertHasCommentLine` "build-log"
+  "remote-build-reporting" `assertHasLine` "remote-build-reporting"
+  "-- report-planning-failure" `assertHasCommentLine` "report-planning-failure"
+  "-- per-component" `assertHasCommentLine` "per-component"
+  "-- run-tests" `assertHasCommentLine` "run-tests"
+  "jobs" `assertHasLine` "jobs"
+  "-- keep-going" `assertHasCommentLine` "keep-going"
+  "-- offline" `assertHasCommentLine` "offline"
+  "-- lib" `assertHasCommentLine` "lib"
+  "-- package-env" `assertHasCommentLine` "package-env"
+  "-- overwrite-policy" `assertHasCommentLine` "overwrite-policy"
+  "-- install-method" `assertHasCommentLine` "install-method"
+  "installdir" `assertHasLine` "installdir"
+  "-- token" `assertHasCommentLine` "token"
+  "-- username" `assertHasCommentLine` "username"
+  "-- password" `assertHasCommentLine` "password"
+  "-- password-command" `assertHasCommentLine` "password-command"
+  "-- builddir" `assertHasCommentLine` "builddir"
+
+  "  -- keep-temp-files" `assertHasCommentLine` "keep-temp-files"
+  "  -- hoogle" `assertHasCommentLine` "hoogle"
+  "  -- html" `assertHasCommentLine` "html"
+  "  -- html-location" `assertHasCommentLine` "html-location"
+  "  -- executables" `assertHasCommentLine` "executables"
+  "  -- foreign-libraries" `assertHasCommentLine` "foreign-libraries"
+  "  -- all" `assertHasCommentLine` "all"
+  "  -- internal" `assertHasCommentLine` "internal"
+  "  -- css" `assertHasCommentLine` "css"
+  "  -- hyperlink-source" `assertHasCommentLine` "hyperlink-source"
+  "  -- quickjump" `assertHasCommentLine` "quickjump"
+  "  -- hscolour-css" `assertHasCommentLine` "hscolour-css"
+  "  -- contents-location" `assertHasCommentLine` "contents-location"
+  "  -- index-location" `assertHasCommentLine` "index-location"
+  "  -- base-url" `assertHasCommentLine` "base-url"
+  "  -- resources-dir" `assertHasCommentLine` "resources-dir"
+  "  -- output-dir" `assertHasCommentLine` "output-dir"
+  "  -- use-unicode" `assertHasCommentLine` "use-unicode"
+
+  "  -- interactive" `assertHasCommentLine` "interactive"
+  "  -- quiet" `assertHasCommentLine` "quiet"
+  "  -- no-comments" `assertHasCommentLine` "no-comments"
+  "  -- minimal" `assertHasCommentLine` "minimal"
+  "  -- cabal-version" `assertHasCommentLine` "cabal-version"
+  "  -- license" `assertHasCommentLine` "license"
+  "  -- extra-doc-file" `assertHasCommentLine` "extra-doc-file"
+  "  -- test-dir" `assertHasCommentLine` "test-dir"
+  "  -- simple" `assertHasCommentLine` "simple"
+  "  -- language" `assertHasCommentLine` "language"
+  "  -- application-dir" `assertHasCommentLine` "application-dir"
+  "  -- source-dir" `assertHasCommentLine` "source-dir"
+
+  "  -- prefix" `assertHasCommentLine` "prefix"
+  "  -- bindir" `assertHasCommentLine` "bindir"
+  "  -- libdir" `assertHasCommentLine` "libdir"
+  "  -- libsubdir" `assertHasCommentLine` "libsubdir"
+  "  -- dynlibdir" `assertHasCommentLine` "dynlibdir"
+  "  -- libexecdir" `assertHasCommentLine` "libexecdir"
+  "  -- libexecsubdir" `assertHasCommentLine` "libexecsubdir"
+  "  -- datadir" `assertHasCommentLine` "datadir"
+  "  -- datasubdir" `assertHasCommentLine` "datasubdir"
+  "  -- docdir" `assertHasCommentLine` "docdir"
+  "  -- htmldir" `assertHasCommentLine` "htmldir"
+  "  -- haddockdir" `assertHasCommentLine` "haddockdir"
+  "  -- sysconfdir" `assertHasCommentLine` "sysconfdir"
+
+  "  -- alex-location" `assertHasCommentLine` "alex-location"
+  "  -- ar-location" `assertHasCommentLine` "ar-location"
+  "  -- c2hs-location" `assertHasCommentLine` "c2hs-location"
+  "  -- cpphs-location" `assertHasCommentLine` "cpphs-location"
+  "  -- doctest-location" `assertHasCommentLine` "doctest-location"
+  "  -- gcc-location" `assertHasCommentLine` "gcc-location"
+  "  -- ghc-location" `assertHasCommentLine` "ghc-location"
+  "  -- ghc-pkg-location" `assertHasCommentLine` "ghc-pkg-location"
+  "  -- ghcjs-location" `assertHasCommentLine` "ghcjs-location"
+  "  -- ghcjs-pkg-location" `assertHasCommentLine` "ghcjs-pkg-location"
+  "  -- greencard-location" `assertHasCommentLine` "greencard-location"
+  "  -- haddock-location" `assertHasCommentLine` "haddock-location"
+  "  -- happy-location" `assertHasCommentLine` "happy-location"
+  "  -- haskell-suite-location" `assertHasCommentLine` "haskell-suite-location"
+  "  -- haskell-suite-pkg-location" `assertHasCommentLine` "haskell-suite-pkg-location"
+  "  -- hmake-location" `assertHasCommentLine` "hmake-location"
+  "  -- hpc-location" `assertHasCommentLine` "hpc-location"
+  "  -- hscolour-location" `assertHasCommentLine` "hscolour-location"
+  "  -- jhc-location" `assertHasCommentLine` "jhc-location"
+  "  -- ld-location" `assertHasCommentLine` "ld-location"
+  "  -- pkg-config-location" `assertHasCommentLine` "pkg-config-location"
+  "  -- runghc-location" `assertHasCommentLine` "runghc-location"
+  "  -- strip-location" `assertHasCommentLine` "strip-location"
+  "  -- tar-location" `assertHasCommentLine` "tar-location"
+  "  -- uhc-location" `assertHasCommentLine` "uhc-location"
+
+  "  -- alex-options" `assertHasCommentLine` "alex-options"
+  "  -- ar-options" `assertHasCommentLine` "ar-options"
+  "  -- c2hs-options" `assertHasCommentLine` "c2hs-options"
+  "  -- cpphs-options" `assertHasCommentLine` "cpphs-options"
+  "  -- doctest-options" `assertHasCommentLine` "doctest-options"
+  "  -- gcc-options" `assertHasCommentLine` "gcc-options"
+  "  -- ghc-options" `assertHasCommentLine` "ghc-options"
+  "  -- ghc-pkg-options" `assertHasCommentLine` "ghc-pkg-options"
+  "  -- ghcjs-options" `assertHasCommentLine` "ghcjs-options"
+  "  -- ghcjs-pkg-options" `assertHasCommentLine` "ghcjs-pkg-options"
+  "  -- greencard-options" `assertHasCommentLine` "greencard-options"
+  "  -- haddock-options" `assertHasCommentLine` "haddock-options"
+  "  -- happy-options" `assertHasCommentLine` "happy-options"
+  "  -- haskell-suite-options" `assertHasCommentLine` "haskell-suite-options"
+  "  -- haskell-suite-pkg-options" `assertHasCommentLine` "haskell-suite-pkg-options"
+  "  -- hmake-options" `assertHasCommentLine` "hmake-options"
+  "  -- hpc-options" `assertHasCommentLine` "hpc-options"
+  "  -- hsc2hs-options" `assertHasCommentLine` "hsc2hs-options"
+  "  -- hscolour-options" `assertHasCommentLine` "hscolour-options"
+  "  -- jhc-options" `assertHasCommentLine` "jhc-options"
+  "  -- ld-options" `assertHasCommentLine` "ld-options"
+  "  -- pkg-config-options" `assertHasCommentLine` "pkg-config-options"
+  "  -- runghc-options" `assertHasCommentLine` "runghc-options"
+  "  -- strip-options" `assertHasCommentLine` "strip-options"
+  "  -- tar-options" `assertHasCommentLine` "tar-options"
+  "  -- uhc-options" `assertHasCommentLine` "uhc-options"
 
 testIgnoreProjectFlag :: Assertion
 testIgnoreProjectFlag = do
diff --git a/cabal-testsuite/PackageTests/Backpack/Includes2/cabal-internal.test.hs b/cabal-testsuite/PackageTests/Backpack/Includes2/cabal-internal.test.hs
index e2c42fe43fd..1413f66dcdc 100644
--- a/cabal-testsuite/PackageTests/Backpack/Includes2/cabal-internal.test.hs
+++ b/cabal-testsuite/PackageTests/Backpack/Includes2/cabal-internal.test.hs
@@ -2,7 +2,7 @@ import Test.Cabal.Prelude
 
 main = cabalTest $ do
     skipUnlessGhcVersion ">= 8.1"
-    expectBrokenIfWindowsCI 10191 $ withProjectFile "cabal.internal.project" $ do
+    withProjectFile "cabal.internal.project" $ do
         cabal "v2-build" ["exe"]
         withPlan $ do
             r <- runPlanExe' "I" "exe" []
diff --git a/cabal-testsuite/PackageTests/Backpack/Includes3/cabal-external.test.hs b/cabal-testsuite/PackageTests/Backpack/Includes3/cabal-external.test.hs
index a2431cdf389..a974254fc98 100644
--- a/cabal-testsuite/PackageTests/Backpack/Includes3/cabal-external.test.hs
+++ b/cabal-testsuite/PackageTests/Backpack/Includes3/cabal-external.test.hs
@@ -2,8 +2,6 @@ import Test.Cabal.Prelude
 
 main = cabalTest $ do
     skipUnlessGhcVersion ">= 8.1"
-    ghcVer <- isGhcVersion ">= 9.10"
-    skipIf "Windows + 9.10.1 (#10191)" (isWindows && ghcVer)
     withProjectFile "cabal.external.project" $ do
         cabal "v2-build" ["exe"]
         withPlan $ do
diff --git a/cabal-testsuite/PackageTests/Backpack/Includes3/cabal-internal.test.hs b/cabal-testsuite/PackageTests/Backpack/Includes3/cabal-internal.test.hs
index b0d3e21688f..81f3fcb0027 100644
--- a/cabal-testsuite/PackageTests/Backpack/Includes3/cabal-internal.test.hs
+++ b/cabal-testsuite/PackageTests/Backpack/Includes3/cabal-internal.test.hs
@@ -2,7 +2,7 @@ import Test.Cabal.Prelude
 
 main = cabalTest $ do
     skipUnlessGhcVersion ">= 8.1"
-    expectBrokenIfWindowsCI 10191 $ withProjectFile "cabal.internal.project" $ do
+    withProjectFile "cabal.internal.project" $ do
         cabal "v2-build" ["exe"]
         withPlan $ do
             r <- runPlanExe' "I" "exe" []
diff --git a/cabal-testsuite/PackageTests/Backpack/T6385/cabal.test.hs b/cabal-testsuite/PackageTests/Backpack/T6385/cabal.test.hs
index d05327839da..5048e09d56b 100644
--- a/cabal-testsuite/PackageTests/Backpack/T6385/cabal.test.hs
+++ b/cabal-testsuite/PackageTests/Backpack/T6385/cabal.test.hs
@@ -1,6 +1,6 @@
 import Test.Cabal.Prelude
 main =
-  cabalTest $ expectBrokenIfWindows 10191 $ withShorterPathForNewBuildStore $ do
+  cabalTest $ withShorterPathForNewBuildStore $ do
     skipUnlessGhcVersion ">= 8.1"
     withRepo "repo" $ do
       cabal "v2-build" ["T6385"]
diff --git a/cabal-testsuite/PackageTests/BuildWays/p/CHANGELOG.md b/cabal-testsuite/PackageTests/BuildWays/p/CHANGELOG.md
new file mode 100644
index 00000000000..9ede8b27d4f
--- /dev/null
+++ b/cabal-testsuite/PackageTests/BuildWays/p/CHANGELOG.md
@@ -0,0 +1,5 @@
+# Revision history for p
+
+## 0.1.0.0 -- YYYY-mm-dd
+
+* First version. Released on an unsuspecting world.
diff --git a/cabal-testsuite/PackageTests/BuildWays/p/p.cabal b/cabal-testsuite/PackageTests/BuildWays/p/p.cabal
new file mode 100644
index 00000000000..687cf16bc0c
--- /dev/null
+++ b/cabal-testsuite/PackageTests/BuildWays/p/p.cabal
@@ -0,0 +1,18 @@
+cabal-version:   3.12
+name:            p
+version:         0.1.0.0
+license:         NONE
+author:          Matthew Pickering
+maintainer:      matthewtpickering@gmail.com
+build-type:      Simple
+extra-doc-files: CHANGELOG.md
+
+common warnings
+    ghc-options: -Wall
+
+library
+    import:           warnings
+    exposed-modules:  MyLib
+    build-depends:    base
+    hs-source-dirs:   src
+    default-language: Haskell2010
diff --git a/cabal-testsuite/PackageTests/BuildWays/p/src/MyLib.hs b/cabal-testsuite/PackageTests/BuildWays/p/src/MyLib.hs
new file mode 100644
index 00000000000..e657c4403f6
--- /dev/null
+++ b/cabal-testsuite/PackageTests/BuildWays/p/src/MyLib.hs
@@ -0,0 +1,4 @@
+module MyLib (someFunc) where
+
+someFunc :: IO ()
+someFunc = putStrLn "someFunc"
diff --git a/cabal-testsuite/PackageTests/BuildWays/q/CHANGELOG.md b/cabal-testsuite/PackageTests/BuildWays/q/CHANGELOG.md
new file mode 100644
index 00000000000..62632c53766
--- /dev/null
+++ b/cabal-testsuite/PackageTests/BuildWays/q/CHANGELOG.md
@@ -0,0 +1,5 @@
+# Revision history for q
+
+## 0.1.0.0 -- YYYY-mm-dd
+
+* First version. Released on an unsuspecting world.
diff --git a/cabal-testsuite/PackageTests/BuildWays/q/app/Main.hs b/cabal-testsuite/PackageTests/BuildWays/q/app/Main.hs
new file mode 100644
index 00000000000..642b418a547
--- /dev/null
+++ b/cabal-testsuite/PackageTests/BuildWays/q/app/Main.hs
@@ -0,0 +1,7 @@
+{-# LANGUAGE TemplateHaskell #-}
+module Main where
+
+import MyLib
+
+main :: IO ()
+main = someFunc
diff --git a/cabal-testsuite/PackageTests/BuildWays/q/q.cabal b/cabal-testsuite/PackageTests/BuildWays/q/q.cabal
new file mode 100644
index 00000000000..a4f2a1d65d7
--- /dev/null
+++ b/cabal-testsuite/PackageTests/BuildWays/q/q.cabal
@@ -0,0 +1,19 @@
+cabal-version:   3.12
+name:            q
+version:         0.1.0.0
+license:         NONE
+author:          Matthew Pickering
+maintainer:      matthewtpickering@gmail.com
+build-type:      Simple
+extra-doc-files: CHANGELOG.md
+
+common warnings
+    ghc-options: -Wall
+
+executable q
+    import:           warnings
+    main-is:          Main.hs
+    build-depends:    p, base
+    hs-source-dirs:   app
+    ghc-options: -dynamic-too
+    default-language: Haskell2010
diff --git a/cabal-testsuite/PackageTests/BuildWays/setup.test.hs b/cabal-testsuite/PackageTests/BuildWays/setup.test.hs
new file mode 100644
index 00000000000..dd4531599e4
--- /dev/null
+++ b/cabal-testsuite/PackageTests/BuildWays/setup.test.hs
@@ -0,0 +1,10 @@
+import Test.Cabal.Prelude
+
+opts = ["--enable-shared", "--enable-library-vanilla", "--enable-library-profiling"]
+
+-- See #10418
+main = setupTest $ recordMode DoNotRecord $ withPackageDb $ do
+    skipIfNoSharedLibraries
+    skipIfNoProfiledLibraries
+    withDirectory "p" $ setup_install opts
+    withDirectory "q" $ setup_install opts
diff --git a/cabal-testsuite/PackageTests/ConfigureComponent/MissingOrPrivate/Lib.cabal b/cabal-testsuite/PackageTests/ConfigureComponent/MissingOrPrivate/Lib.cabal
new file mode 100644
index 00000000000..284513bd8b1
--- /dev/null
+++ b/cabal-testsuite/PackageTests/ConfigureComponent/MissingOrPrivate/Lib.cabal
@@ -0,0 +1,20 @@
+cabal-version:       3.0
+name:                Lib
+version:             0.1.0.0
+license:             BSD-3-Clause
+author:              Edward Z. Yang
+maintainer:          ezyang@cs.stanford.edu
+build-type:          Simple
+
+library foo-internal
+  build-depends:       base
+  exposed-modules:     Lib
+  default-language:    Haskell2010
+
+executable exe
+  main-is:             Exe.hs
+  build-depends:       base <=1.0,
+                       package-that-does-not-exist,
+                       Lib:{foo-internal, bar-internal},
+  hs-source-dirs:      exe
+  default-language:    Haskell2010
diff --git a/cabal-testsuite/PackageTests/ConfigureComponent/MissingOrPrivate/Lib.hs b/cabal-testsuite/PackageTests/ConfigureComponent/MissingOrPrivate/Lib.hs
new file mode 100644
index 00000000000..1d7d07d5cba
--- /dev/null
+++ b/cabal-testsuite/PackageTests/ConfigureComponent/MissingOrPrivate/Lib.hs
@@ -0,0 +1,2 @@
+module Lib where
+lib = "OK"
diff --git a/cabal-testsuite/PackageTests/ConfigureComponent/MissingOrPrivate/exe/Exe.hs b/cabal-testsuite/PackageTests/ConfigureComponent/MissingOrPrivate/exe/Exe.hs
new file mode 100644
index 00000000000..6ee3fb933aa
--- /dev/null
+++ b/cabal-testsuite/PackageTests/ConfigureComponent/MissingOrPrivate/exe/Exe.hs
@@ -0,0 +1,2 @@
+import Lib
+main = putStrLn lib
diff --git a/cabal-testsuite/PackageTests/ConfigureComponent/MissingOrPrivate/setup-fail.out b/cabal-testsuite/PackageTests/ConfigureComponent/MissingOrPrivate/setup-fail.out
new file mode 100644
index 00000000000..2ea38e253cd
--- /dev/null
+++ b/cabal-testsuite/PackageTests/ConfigureComponent/MissingOrPrivate/setup-fail.out
@@ -0,0 +1,16 @@
+# Setup configure
+Configuring library 'foo-internal' for Lib-0.1.0.0...
+# Setup build
+Preprocessing library 'foo-internal' for Lib-0.1.0.0...
+Building library 'foo-internal' for Lib-0.1.0.0...
+# Setup copy
+Installing internal library foo-internal in <PATH>
+# Setup register
+Registering library 'foo-internal' for Lib-0.1.0.0...
+# Setup configure
+Configuring executable 'exe' for Lib-0.1.0.0...
+Error: [Cabal-8010]
+Encountered missing or private dependencies:
+    Lib:{bar-internal,foo-internal} (missing :bar-internal),
+    base <=1.0 (installed: <VERSION>),
+    package-that-does-not-exist (missing)
diff --git a/cabal-testsuite/PackageTests/ConfigureComponent/MissingOrPrivate/setup-fail.test.hs b/cabal-testsuite/PackageTests/ConfigureComponent/MissingOrPrivate/setup-fail.test.hs
new file mode 100644
index 00000000000..5d8123ee88c
--- /dev/null
+++ b/cabal-testsuite/PackageTests/ConfigureComponent/MissingOrPrivate/setup-fail.test.hs
@@ -0,0 +1,8 @@
+
+import Test.Cabal.Prelude
+main = setupTest $ do
+    withPackageDb $ do
+        base_id <- getIPID "base"
+        setup_install ["foo-internal", "--cid", "foo-internal-0.1-abc"]
+        r <- fails $ setup' "configure" [ "exe" ]
+        assertOutputContains "Lib" r
diff --git a/cabal-testsuite/PackageTests/ConfigureComponent/SubLib/setup-explicit-fail.out b/cabal-testsuite/PackageTests/ConfigureComponent/SubLib/setup-explicit-fail.out
index fec347864e5..ee7258799b1 100644
--- a/cabal-testsuite/PackageTests/ConfigureComponent/SubLib/setup-explicit-fail.out
+++ b/cabal-testsuite/PackageTests/ConfigureComponent/SubLib/setup-explicit-fail.out
@@ -11,4 +11,4 @@ Registering library 'sublib' for Lib-0.1.0.0...
 Configuring executable 'exe' for Lib-0.1.0.0...
 Error: [Cabal-8010]
 Encountered missing or private dependencies:
-    Lib:sublib
+    Lib:sublib (missing :sublib)
diff --git a/cabal-testsuite/PackageTests/HaddockKeepTmpsCustom/Setup.hs b/cabal-testsuite/PackageTests/HaddockKeepTmpsCustom/Setup.hs
new file mode 100644
index 00000000000..e8ef27dbba9
--- /dev/null
+++ b/cabal-testsuite/PackageTests/HaddockKeepTmpsCustom/Setup.hs
@@ -0,0 +1,3 @@
+import Distribution.Simple
+
+main = defaultMain
diff --git a/cabal-testsuite/PackageTests/HaddockKeepTmpsCustom/Simple.hs b/cabal-testsuite/PackageTests/HaddockKeepTmpsCustom/Simple.hs
new file mode 100644
index 00000000000..df38c448c5e
--- /dev/null
+++ b/cabal-testsuite/PackageTests/HaddockKeepTmpsCustom/Simple.hs
@@ -0,0 +1,4 @@
+module Simple where
+
+-- | For hiding needles.
+data Haystack = Haystack
diff --git a/cabal-testsuite/PackageTests/HaddockKeepTmpsCustom/cabal.project b/cabal-testsuite/PackageTests/HaddockKeepTmpsCustom/cabal.project
new file mode 100644
index 00000000000..f45d5a19d3c
--- /dev/null
+++ b/cabal-testsuite/PackageTests/HaddockKeepTmpsCustom/cabal.project
@@ -0,0 +1,3 @@
+packages: .
+
+haddock-keep-temp-files: true
diff --git a/cabal-testsuite/PackageTests/HaddockKeepTmpsCustom/cabal.test.hs b/cabal-testsuite/PackageTests/HaddockKeepTmpsCustom/cabal.test.hs
new file mode 100644
index 00000000000..e2d819e44d6
--- /dev/null
+++ b/cabal-testsuite/PackageTests/HaddockKeepTmpsCustom/cabal.test.hs
@@ -0,0 +1,22 @@
+import Test.Cabal.Prelude
+
+-- Test that "cabal haddock" preserves temporary files
+-- We use haddock-keep-temp-file: True in the cabal.project.
+main = cabalTest $ recordMode DoNotRecord $ withProjectFile "cabal.project" $ do
+  cabal "haddock" []
+
+  -- From the docs for `System.IO.openTempFile`:
+  --
+  --   On Windows, the template prefix may be truncated to 3 chars, e.g.
+  --   "foobar.ext" will be "fooXXX.ext".
+  let glob =
+        if isWindows
+          then "had*.txt"
+          else "haddock-response*.txt"
+
+  -- Check that there is a response file.
+  responseFiles <- assertGlobMatchesTestDir testTmpDir glob
+
+  -- Check that the matched response file is not empty, and is indeed a Haddock
+  -- response file.
+  assertAnyFileContains responseFiles "--package-name"
diff --git a/cabal-testsuite/PackageTests/HaddockKeepTmpsCustom/my.cabal b/cabal-testsuite/PackageTests/HaddockKeepTmpsCustom/my.cabal
new file mode 100644
index 00000000000..a4a24980c12
--- /dev/null
+++ b/cabal-testsuite/PackageTests/HaddockKeepTmpsCustom/my.cabal
@@ -0,0 +1,16 @@
+cabal-version: 3.0
+name: HaddockKeepsTmpsCustom
+version: 0.1
+license: BSD-3-Clause
+author: Rodrigo Mesquita
+stability: stable
+category: PackageTests
+build-type: Custom
+
+custom-setup
+    setup-depends: Cabal, base
+
+library
+    default-language: Haskell2010
+    exposed-modules: Simple
+    build-depends: base
diff --git a/cabal-testsuite/PackageTests/HaddockKeepsTmps/cabal.test.hs b/cabal-testsuite/PackageTests/HaddockKeepsTmps/cabal.test.hs
index a4db6795625..3a76caadf6c 100644
--- a/cabal-testsuite/PackageTests/HaddockKeepsTmps/cabal.test.hs
+++ b/cabal-testsuite/PackageTests/HaddockKeepsTmps/cabal.test.hs
@@ -1,21 +1,29 @@
-{-# LANGUAGE LambdaCase #-}
-import Test.Cabal.Prelude
-import Data.List (sort)
-import Distribution.Verbosity
+import Data.List (isPrefixOf, sort)
 import Distribution.Simple.Glob
 import Distribution.Simple.Glob.Internal
 import Distribution.Simple.Utils
+import Distribution.Verbosity
+import System.Directory
+import Test.Cabal.Prelude
 
 -- Test that "cabal haddock" preserves temporary files
 -- We use haddock-keep-temp-file: True in the cabal.project.
-main = cabalTest $ recordMode DoNotRecord $ withProjectFile "cabal.project" $ do
+main =
+  cabalTest $ recordMode DoNotRecord $ withProjectFile "cabal.project" $ do
     cabal "haddock" []
 
-    cwd <- fmap testCurrentDir getTestEnv
+    -- From the docs for `System.IO.openTempFile`:
+    --
+    --   On Windows, the template prefix may be truncated to 3 chars, e.g.
+    --   "foobar.ext" will be "fooXXX.ext".
+    let glob =
+          if isWindows
+            then "had*.txt"
+            else "haddock-response*.txt"
+
+    -- Check that there is a response file.
+    responseFiles <- assertGlobMatchesTestDir testTmpDir glob
 
-    -- Windows has multiple response files, and only the last one (alphabetically) is the important one.
-    (safeLast . sort . globMatches <$> liftIO (runDirFileGlob silent Nothing cwd (GlobDirRecursive [WildCard, Literal "txt"]))) >>= \case
-      Nothing -> error "Expecting a response file to exist"
-      Just m -> do
-        -- Assert the matched response file is not empty, and indeed a haddock rsp
-        assertFileDoesContain (cwd </> m) "--package-name"
+    -- Check that the matched response file is not empty, and is indeed a Haddock
+    -- response file.
+    assertAnyFileContains responseFiles "--package-name"
diff --git a/cabal-testsuite/PackageTests/Install/DistPrefInstall/CHANGELOG.md b/cabal-testsuite/PackageTests/Install/DistPrefInstall/CHANGELOG.md
new file mode 100644
index 00000000000..3d5552b0ba5
--- /dev/null
+++ b/cabal-testsuite/PackageTests/Install/DistPrefInstall/CHANGELOG.md
@@ -0,0 +1,5 @@
+# Revision history for DistPrefInstall
+
+## 0.1.0.0 -- YYYY-mm-dd
+
+* First version. Released on an unsuspecting world.
diff --git a/cabal-testsuite/PackageTests/Install/DistPrefInstall/DistPrefInstall.cabal b/cabal-testsuite/PackageTests/Install/DistPrefInstall/DistPrefInstall.cabal
new file mode 100644
index 00000000000..536d26b3648
--- /dev/null
+++ b/cabal-testsuite/PackageTests/Install/DistPrefInstall/DistPrefInstall.cabal
@@ -0,0 +1,18 @@
+cabal-version:   3.12
+name:            DistPrefInstall
+version:         0.1.0.0
+license:         NONE
+author:          Matthew Pickering
+maintainer:      matthewtpickering@gmail.com
+build-type:      Simple
+extra-doc-files: CHANGELOG.md
+
+common warnings
+    ghc-options: -Wall
+
+library
+    import:           warnings
+    exposed-modules:  MyLib
+    build-depends:    base
+    hs-source-dirs:   src
+    default-language: Haskell2010
diff --git a/cabal-testsuite/PackageTests/Install/DistPrefInstall/Setup.hs b/cabal-testsuite/PackageTests/Install/DistPrefInstall/Setup.hs
new file mode 100644
index 00000000000..9a994af677b
--- /dev/null
+++ b/cabal-testsuite/PackageTests/Install/DistPrefInstall/Setup.hs
@@ -0,0 +1,2 @@
+import Distribution.Simple
+main = defaultMain
diff --git a/cabal-testsuite/PackageTests/Install/DistPrefInstall/setup.test.hs b/cabal-testsuite/PackageTests/Install/DistPrefInstall/setup.test.hs
new file mode 100644
index 00000000000..27b709e7070
--- /dev/null
+++ b/cabal-testsuite/PackageTests/Install/DistPrefInstall/setup.test.hs
@@ -0,0 +1,8 @@
+import Test.Cabal.Prelude
+
+main = setupTest $ recordMode DoNotRecord $ withPackageDb $ do
+    setup "configure" []
+    setup "build" []
+    setup "copy" []
+    setup "install" []
+    setup "sdist" []
diff --git a/cabal-testsuite/PackageTests/Install/DistPrefInstall/src/MyLib.hs b/cabal-testsuite/PackageTests/Install/DistPrefInstall/src/MyLib.hs
new file mode 100644
index 00000000000..e657c4403f6
--- /dev/null
+++ b/cabal-testsuite/PackageTests/Install/DistPrefInstall/src/MyLib.hs
@@ -0,0 +1,4 @@
+module MyLib (someFunc) where
+
+someFunc :: IO ()
+someFunc = putStrLn "someFunc"
diff --git a/cabal-testsuite/PackageTests/MultiRepl/CustomSetupKeepTempFiles/cabal.no.out b/cabal-testsuite/PackageTests/MultiRepl/CustomSetupKeepTempFiles/cabal.no.out
new file mode 100644
index 00000000000..073e87feea2
--- /dev/null
+++ b/cabal-testsuite/PackageTests/MultiRepl/CustomSetupKeepTempFiles/cabal.no.out
@@ -0,0 +1,11 @@
+# cabal clean
+# cabal v2-repl
+Resolving dependencies...
+Build profile: -w ghc-<GHCVER> -O1
+In order, the following will be built:
+ - pkg-a-1 (interactive) (first run)
+ - pkg-b-0 (interactive) (first run)
+Configuring pkg-a-1...
+Preprocessing library for pkg-a-1...
+Configuring pkg-b-0...
+Preprocessing library for pkg-b-0...
diff --git a/cabal-testsuite/PackageTests/MultiRepl/CustomSetupKeepTempFiles/cabal.out b/cabal-testsuite/PackageTests/MultiRepl/CustomSetupKeepTempFiles/cabal.out
new file mode 100644
index 00000000000..9c141d7ac42
--- /dev/null
+++ b/cabal-testsuite/PackageTests/MultiRepl/CustomSetupKeepTempFiles/cabal.out
@@ -0,0 +1,10 @@
+# cabal v2-repl
+Resolving dependencies...
+Build profile: -w ghc-<GHCVER> -O1
+In order, the following will be built:
+ - pkg-a-1 (interactive) (lib) (first run)
+ - pkg-b-0 (interactive) (lib) (first run)
+Configuring library for pkg-a-1...
+Preprocessing library for pkg-a-1...
+Configuring library for pkg-b-0...
+Preprocessing library for pkg-b-0...
diff --git a/cabal-testsuite/PackageTests/MultiRepl/CustomSetupKeepTempFiles/cabal.project b/cabal-testsuite/PackageTests/MultiRepl/CustomSetupKeepTempFiles/cabal.project
new file mode 100644
index 00000000000..bf8292adeb5
--- /dev/null
+++ b/cabal-testsuite/PackageTests/MultiRepl/CustomSetupKeepTempFiles/cabal.project
@@ -0,0 +1,2 @@
+packages: pkg-a/*.cabal
+packages: pkg-b/*.cabal
diff --git a/cabal-testsuite/PackageTests/MultiRepl/CustomSetupKeepTempFiles/cabal.test.hs b/cabal-testsuite/PackageTests/MultiRepl/CustomSetupKeepTempFiles/cabal.test.hs
new file mode 100644
index 00000000000..ea0851f1f2c
--- /dev/null
+++ b/cabal-testsuite/PackageTests/MultiRepl/CustomSetupKeepTempFiles/cabal.test.hs
@@ -0,0 +1,33 @@
+import Test.Cabal.Prelude
+
+main = do
+  cabalTest' "yes" $ do
+    skipUnlessAnyCabalVersion ">= 3.11"
+    skipUnlessGhcVersion ">= 9.4"
+    cabal' "clean" []
+    res <-
+      cabalWithStdin
+        "v2-repl"
+        [ "--keep-temp-files"
+        , "--enable-multi-repl"
+        , "pkg-b"
+        , "pkg-a"
+        ]
+        "Bar.bar"
+    assertOutputContains "foo is 42" res
+    void $ assertGlobMatchesTestDir testDistDir "multi-out*/"
+
+  cabalTest' "no" $ do
+    skipUnlessAnyCabalVersion ">= 3.11"
+    skipUnlessGhcVersion ">= 9.4"
+    cabal' "clean" []
+    res <-
+      cabalWithStdin
+        "v2-repl"
+        [ "--enable-multi-repl"
+        , "pkg-b"
+        , "pkg-a"
+        ]
+        "Bar.bar"
+    assertOutputContains "foo is 42" res
+    void $ assertGlobDoesNotMatchTestDir testDistDir "multi-out*/"
diff --git a/cabal-testsuite/PackageTests/MultiRepl/CustomSetupKeepTempFiles/cabal.yes.out b/cabal-testsuite/PackageTests/MultiRepl/CustomSetupKeepTempFiles/cabal.yes.out
new file mode 100644
index 00000000000..073e87feea2
--- /dev/null
+++ b/cabal-testsuite/PackageTests/MultiRepl/CustomSetupKeepTempFiles/cabal.yes.out
@@ -0,0 +1,11 @@
+# cabal clean
+# cabal v2-repl
+Resolving dependencies...
+Build profile: -w ghc-<GHCVER> -O1
+In order, the following will be built:
+ - pkg-a-1 (interactive) (first run)
+ - pkg-b-0 (interactive) (first run)
+Configuring pkg-a-1...
+Preprocessing library for pkg-a-1...
+Configuring pkg-b-0...
+Preprocessing library for pkg-b-0...
diff --git a/cabal-testsuite/PackageTests/MultiRepl/CustomSetupKeepTempFiles/pkg-a/Foo.hs b/cabal-testsuite/PackageTests/MultiRepl/CustomSetupKeepTempFiles/pkg-a/Foo.hs
new file mode 100644
index 00000000000..208f04764de
--- /dev/null
+++ b/cabal-testsuite/PackageTests/MultiRepl/CustomSetupKeepTempFiles/pkg-a/Foo.hs
@@ -0,0 +1,4 @@
+module Foo where
+
+foo :: Int
+foo = 42
diff --git a/cabal-testsuite/PackageTests/MultiRepl/CustomSetupKeepTempFiles/pkg-a/Setup.hs b/cabal-testsuite/PackageTests/MultiRepl/CustomSetupKeepTempFiles/pkg-a/Setup.hs
new file mode 100644
index 00000000000..00bfe1fe441
--- /dev/null
+++ b/cabal-testsuite/PackageTests/MultiRepl/CustomSetupKeepTempFiles/pkg-a/Setup.hs
@@ -0,0 +1,4 @@
+import Distribution.Simple
+
+main :: IO ()
+main = defaultMain
diff --git a/cabal-testsuite/PackageTests/MultiRepl/CustomSetupKeepTempFiles/pkg-a/pkg-a.cabal b/cabal-testsuite/PackageTests/MultiRepl/CustomSetupKeepTempFiles/pkg-a/pkg-a.cabal
new file mode 100644
index 00000000000..3c3bbde21a2
--- /dev/null
+++ b/cabal-testsuite/PackageTests/MultiRepl/CustomSetupKeepTempFiles/pkg-a/pkg-a.cabal
@@ -0,0 +1,12 @@
+cabal-version: 2.2
+name: pkg-a
+version: 1
+build-type: Custom
+
+custom-setup
+  setup-depends: Cabal, base
+
+library
+  default-language: Haskell2010
+  build-depends: base
+  exposed-modules: Foo
diff --git a/cabal-testsuite/PackageTests/MultiRepl/CustomSetupKeepTempFiles/pkg-b/Bar.hs b/cabal-testsuite/PackageTests/MultiRepl/CustomSetupKeepTempFiles/pkg-b/Bar.hs
new file mode 100644
index 00000000000..114eedd9306
--- /dev/null
+++ b/cabal-testsuite/PackageTests/MultiRepl/CustomSetupKeepTempFiles/pkg-b/Bar.hs
@@ -0,0 +1,6 @@
+module Bar (foo, bar) where
+
+import Foo (foo)
+
+bar :: String
+bar = "foo is " <> show foo
diff --git a/cabal-testsuite/PackageTests/MultiRepl/CustomSetupKeepTempFiles/pkg-b/Setup.hs b/cabal-testsuite/PackageTests/MultiRepl/CustomSetupKeepTempFiles/pkg-b/Setup.hs
new file mode 100644
index 00000000000..00bfe1fe441
--- /dev/null
+++ b/cabal-testsuite/PackageTests/MultiRepl/CustomSetupKeepTempFiles/pkg-b/Setup.hs
@@ -0,0 +1,4 @@
+import Distribution.Simple
+
+main :: IO ()
+main = defaultMain
diff --git a/cabal-testsuite/PackageTests/MultiRepl/CustomSetupKeepTempFiles/pkg-b/pkg-b.cabal b/cabal-testsuite/PackageTests/MultiRepl/CustomSetupKeepTempFiles/pkg-b/pkg-b.cabal
new file mode 100644
index 00000000000..a354090771d
--- /dev/null
+++ b/cabal-testsuite/PackageTests/MultiRepl/CustomSetupKeepTempFiles/pkg-b/pkg-b.cabal
@@ -0,0 +1,12 @@
+cabal-version: 2.2
+name: pkg-b
+version: 0
+build-type: Custom
+
+custom-setup
+  setup-depends: Cabal, base
+
+library
+  default-language: Haskell2010
+  build-depends: base, pkg-a
+  exposed-modules: Bar
diff --git a/cabal-testsuite/PackageTests/MultiRepl/KeepTempFiles/cabal.no.out b/cabal-testsuite/PackageTests/MultiRepl/KeepTempFiles/cabal.no.out
new file mode 100644
index 00000000000..348fea760af
--- /dev/null
+++ b/cabal-testsuite/PackageTests/MultiRepl/KeepTempFiles/cabal.no.out
@@ -0,0 +1,11 @@
+# cabal clean
+# cabal v2-repl
+Resolving dependencies...
+Build profile: -w ghc-<GHCVER> -O1
+In order, the following will be built:
+ - pkg-a-1 (interactive) (lib) (first run)
+ - pkg-b-0 (interactive) (lib) (first run)
+Configuring library for pkg-a-1...
+Preprocessing library for pkg-a-1...
+Configuring library for pkg-b-0...
+Preprocessing library for pkg-b-0...
diff --git a/cabal-testsuite/PackageTests/MultiRepl/KeepTempFiles/cabal.project b/cabal-testsuite/PackageTests/MultiRepl/KeepTempFiles/cabal.project
new file mode 100644
index 00000000000..bf8292adeb5
--- /dev/null
+++ b/cabal-testsuite/PackageTests/MultiRepl/KeepTempFiles/cabal.project
@@ -0,0 +1,2 @@
+packages: pkg-a/*.cabal
+packages: pkg-b/*.cabal
diff --git a/cabal-testsuite/PackageTests/MultiRepl/KeepTempFiles/cabal.test.hs b/cabal-testsuite/PackageTests/MultiRepl/KeepTempFiles/cabal.test.hs
new file mode 100644
index 00000000000..26c90db7ab1
--- /dev/null
+++ b/cabal-testsuite/PackageTests/MultiRepl/KeepTempFiles/cabal.test.hs
@@ -0,0 +1,31 @@
+import Test.Cabal.Prelude
+
+main = do
+  cabalTest' "yes" $ do
+    skipUnlessGhcVersion ">= 9.4"
+    cabal' "clean" []
+    res <-
+      cabalWithStdin
+        "v2-repl"
+        [ "--keep-temp-files"
+        , "--enable-multi-repl"
+        , "pkg-b"
+        , "pkg-a"
+        ]
+        "Bar.bar"
+    assertOutputContains "foo is 42" res
+    void $ assertGlobMatchesTestDir testDistDir "multi-out*/"
+
+  cabalTest' "no" $ do
+    skipUnlessGhcVersion ">= 9.4"
+    cabal' "clean" []
+    res <-
+      cabalWithStdin
+        "v2-repl"
+        [ "--enable-multi-repl"
+        , "pkg-b"
+        , "pkg-a"
+        ]
+        "Bar.bar"
+    assertOutputContains "foo is 42" res
+    void $ assertGlobDoesNotMatchTestDir testDistDir "multi-out*/"
diff --git a/cabal-testsuite/PackageTests/MultiRepl/KeepTempFiles/cabal.yes.out b/cabal-testsuite/PackageTests/MultiRepl/KeepTempFiles/cabal.yes.out
new file mode 100644
index 00000000000..348fea760af
--- /dev/null
+++ b/cabal-testsuite/PackageTests/MultiRepl/KeepTempFiles/cabal.yes.out
@@ -0,0 +1,11 @@
+# cabal clean
+# cabal v2-repl
+Resolving dependencies...
+Build profile: -w ghc-<GHCVER> -O1
+In order, the following will be built:
+ - pkg-a-1 (interactive) (lib) (first run)
+ - pkg-b-0 (interactive) (lib) (first run)
+Configuring library for pkg-a-1...
+Preprocessing library for pkg-a-1...
+Configuring library for pkg-b-0...
+Preprocessing library for pkg-b-0...
diff --git a/cabal-testsuite/PackageTests/MultiRepl/KeepTempFiles/pkg-a/Foo.hs b/cabal-testsuite/PackageTests/MultiRepl/KeepTempFiles/pkg-a/Foo.hs
new file mode 100644
index 00000000000..208f04764de
--- /dev/null
+++ b/cabal-testsuite/PackageTests/MultiRepl/KeepTempFiles/pkg-a/Foo.hs
@@ -0,0 +1,4 @@
+module Foo where
+
+foo :: Int
+foo = 42
diff --git a/cabal-testsuite/PackageTests/MultiRepl/KeepTempFiles/pkg-a/pkg-a.cabal b/cabal-testsuite/PackageTests/MultiRepl/KeepTempFiles/pkg-a/pkg-a.cabal
new file mode 100644
index 00000000000..7e4a3e9ef70
--- /dev/null
+++ b/cabal-testsuite/PackageTests/MultiRepl/KeepTempFiles/pkg-a/pkg-a.cabal
@@ -0,0 +1,8 @@
+cabal-version: 2.2
+name: pkg-a
+version: 1
+
+library
+  default-language: Haskell2010
+  build-depends: base
+  exposed-modules: Foo
diff --git a/cabal-testsuite/PackageTests/MultiRepl/KeepTempFiles/pkg-b/Bar.hs b/cabal-testsuite/PackageTests/MultiRepl/KeepTempFiles/pkg-b/Bar.hs
new file mode 100644
index 00000000000..114eedd9306
--- /dev/null
+++ b/cabal-testsuite/PackageTests/MultiRepl/KeepTempFiles/pkg-b/Bar.hs
@@ -0,0 +1,6 @@
+module Bar (foo, bar) where
+
+import Foo (foo)
+
+bar :: String
+bar = "foo is " <> show foo
diff --git a/cabal-testsuite/PackageTests/MultiRepl/KeepTempFiles/pkg-b/pkg-b.cabal b/cabal-testsuite/PackageTests/MultiRepl/KeepTempFiles/pkg-b/pkg-b.cabal
new file mode 100644
index 00000000000..8e1a273f0c4
--- /dev/null
+++ b/cabal-testsuite/PackageTests/MultiRepl/KeepTempFiles/pkg-b/pkg-b.cabal
@@ -0,0 +1,8 @@
+cabal-version: 2.2
+name: pkg-b
+version: 0
+
+library
+  default-language: Haskell2010
+  build-depends: base, pkg-a
+  exposed-modules: Bar
diff --git a/cabal-testsuite/cabal-testsuite.cabal b/cabal-testsuite/cabal-testsuite.cabal
index 4c114082d43..f0dce35e60e 100644
--- a/cabal-testsuite/cabal-testsuite.cabal
+++ b/cabal-testsuite/cabal-testsuite.cabal
@@ -70,6 +70,7 @@ library
     , directory             ^>= 1.2.0.1 || ^>= 1.3.0.0
     , exceptions            ^>= 0.10.0
     , filepath              ^>= 1.3.0.1 || ^>= 1.4.0.0 || ^>= 1.5.0.0
+    , Glob                  ^>= 0.10.2
     , network-wait          ^>= 0.1.2.0 || ^>= 0.2.0.0
     , optparse-applicative  ^>= 0.14.3.0 || ^>=0.15.1.0 || ^>=0.16.0.0 || ^>= 0.17.0.0 || ^>= 0.18.1.0
     , process               ^>= 1.2.1.0 || ^>= 1.4.2.0 || ^>= 1.6.1.0
diff --git a/cabal-testsuite/src/Test/Cabal/Monad.hs b/cabal-testsuite/src/Test/Cabal/Monad.hs
index abb9fba5def..31e1e07bf52 100644
--- a/cabal-testsuite/src/Test/Cabal/Monad.hs
+++ b/cabal-testsuite/src/Test/Cabal/Monad.hs
@@ -402,14 +402,18 @@ runTestM mode m =
                     testSkipSetupTests =  argSkipSetupTests (testCommonArgs args),
                     testHaveCabalShared = runnerWithSharedLib senv,
                     testEnvironment =
-                        -- Try to avoid Unicode output
-                        [ ("LC_ALL", Just "C")
+                        -- Use UTF-8 output on all platforms.
+                        [ ("LC_ALL", Just "en_US.UTF-8")
                         -- Hermetic builds (knot-tied)
                         , ("HOME", Just (testHomeDir env))
                         -- Set CABAL_DIR in addition to HOME, since HOME has no
                         -- effect on Windows.
                         , ("CABAL_DIR", Just (testCabalDir env))
                         , ("CABAL_CONFIG", Just (testUserCabalConfigFile env))
+                        -- Set `TMPDIR` so that temporary files aren't created in the global `TMPDIR`.
+                        , ("TMPDIR", Just tmp_dir)
+                        -- Windows uses `TMP` for the `TMPDIR`.
+                        , ("TMP", Just tmp_dir)
                         ],
                     testShouldFail = False,
                     testRelativeCurrentDir = ".",
diff --git a/cabal-testsuite/src/Test/Cabal/OutputNormalizer.hs b/cabal-testsuite/src/Test/Cabal/OutputNormalizer.hs
index 33e1522526b..fb2840be9e6 100644
--- a/cabal-testsuite/src/Test/Cabal/OutputNormalizer.hs
+++ b/cabal-testsuite/src/Test/Cabal/OutputNormalizer.hs
@@ -80,6 +80,7 @@ normalizeOutput nenv =
   . maybe id normalizePathCmdOutput (normalizerCabalInstallVersion nenv)
   -- hackage-security locks occur non-deterministically
   . resub "(Released|Acquired|Waiting) .*hackage-security-lock\n" ""
+  . resub "installed: [0-9]+(\\.[0-9]+)*" "installed: <VERSION>"
   where
     sameDir = "(\\.((\\\\)+|\\/))*"
     packageIdRegex pid =
diff --git a/cabal-testsuite/src/Test/Cabal/Prelude.hs b/cabal-testsuite/src/Test/Cabal/Prelude.hs
index 50f9395d74a..d8cee954d83 100644
--- a/cabal-testsuite/src/Test/Cabal/Prelude.hs
+++ b/cabal-testsuite/src/Test/Cabal/Prelude.hs
@@ -53,9 +53,9 @@ import Text.Regex.TDFA ((=~))
 import Control.Concurrent.Async (withAsync)
 import qualified Data.Aeson as JSON
 import qualified Data.ByteString.Lazy as BSL
-import Control.Monad (unless, when, void, forM_, liftM2, liftM4)
+import Control.Monad (unless, when, void, forM_, foldM, liftM2, liftM4)
 import Control.Monad.Catch ( bracket_ )
-import Control.Monad.Trans.Reader (withReaderT, runReaderT)
+import Control.Monad.Trans.Reader (asks, withReaderT, runReaderT)
 import Control.Monad.IO.Class (MonadIO (..))
 import qualified Crypto.Hash.SHA256 as SHA256
 import qualified Data.ByteString.Base16 as Base16
@@ -70,6 +70,7 @@ import System.Directory
 import Control.Retry (exponentialBackoff, limitRetriesByCumulativeDelay)
 import Network.Wait (waitTcpVerbose)
 import System.Environment
+import qualified System.FilePath.Glob as Glob (globDir1, compile)
 import System.Process
 import System.IO
 
@@ -726,7 +727,7 @@ recordHeader args = do
 
 ------------------------------------------------------------------------
 -- * Subprocess run results
-assertFailure :: WithCallStack (String -> m ())
+assertFailure :: WithCallStack (String -> m a)
 assertFailure msg = withFrozenCallStack $ error msg
 
 assertExitCode :: MonadIO m => WithCallStack (ExitCode -> Result -> m ())
@@ -835,6 +836,31 @@ assertFileDoesNotContain path needle =
                        (assertFailure ("expected: " ++ needle ++ "\n" ++
                                        " in file: " ++ path)))
 
+-- | Assert that at least one of the given paths contains the given search string.
+assertAnyFileContains :: MonadIO m => WithCallStack ([FilePath] -> String -> m ())
+assertAnyFileContains paths needle = do
+    let findOne found path =
+            if found
+               then pure found
+               else withFileContents path $ \contents ->
+                   pure $! needle `isInfixOf` contents
+    foundNeedle <- liftIO $ foldM findOne False paths
+    withFrozenCallStack $
+      unless foundNeedle $
+        assertFailure $
+          "expected: " <>
+          needle <>
+          "\nin one of:\n" <>
+          unlines (map ("* " <>) paths)
+
+-- | Assert that none of the given paths contains the given search string.
+assertNoFileContains :: MonadIO m => WithCallStack ([FilePath] -> String -> m ())
+assertNoFileContains paths needle =
+    liftIO $
+      forM_ paths $
+        \path ->
+          assertFileDoesNotContain path needle
+
 -- | Replace line breaks with spaces, correctly handling "\r\n".
 concatOutput :: String -> String
 concatOutput = unwords . lines . filter ((/=) '\r')
@@ -847,6 +873,58 @@ getScriptCacheDirectory script = do
     let hash = C.unpack . Base16.encode . C.take 26 . SHA256.hash . C.pack $ hashinput
     return $ cabalDir </> "script-builds" </> hash
 
+------------------------------------------------------------------------
+-- * Globs
+
+-- | Match a glob from a root directory and return the results.
+matchGlob :: MonadIO m => FilePath -> String -> m [FilePath]
+matchGlob root glob = do
+  liftIO $ Glob.globDir1 (Glob.compile glob) root
+
+-- | Assert that a glob matches at least one path in the given root directory.
+--
+-- The matched paths are returned for further validation.
+assertGlobMatches :: MonadIO m => WithCallStack (FilePath -> String -> m [FilePath])
+assertGlobMatches root glob = do
+  results <- matchGlob root glob
+  withFrozenCallStack $
+    when (null results) $
+      assertFailure $
+        "Expected glob " <> show glob <> " to match in " <> show root
+  pure results
+
+-- | Assert that a glob matches no paths in the given root directory.
+assertGlobDoesNotMatch :: MonadIO m => WithCallStack (FilePath -> String -> m ())
+assertGlobDoesNotMatch root glob = do
+  results <- matchGlob root glob
+  withFrozenCallStack $
+    unless (null results) $
+      assertFailure $
+        "Expected glob "
+          <> show glob
+          <> " to not match any paths in "
+          <> show root
+          <> ", but the following matches were found:"
+          <> unlines (map ("* " <>) results)
+
+-- | Assert that a glob matches a path in the given root directory.
+--
+-- The root directory is determined from the `TestEnv` with a function like `testDistDir`.
+--
+-- The matched paths are returned for further validation.
+assertGlobMatchesTestDir :: WithCallStack ((TestEnv -> FilePath) -> String -> TestM [FilePath])
+assertGlobMatchesTestDir rootSelector glob = do
+  root <- asks rootSelector
+  assertGlobMatches root glob
+
+-- | Assert that a glob matches a path in the given root directory.
+--
+-- The root directory is determined from the `TestEnv` with a function like `testDistDir`.
+assertGlobDoesNotMatchTestDir :: WithCallStack ((TestEnv -> FilePath) -> String -> TestM ())
+assertGlobDoesNotMatchTestDir rootSelector glob = do
+  root <- asks rootSelector
+  assertGlobDoesNotMatch root glob
+
 ------------------------------------------------------------------------
 -- * Skipping tests
 
diff --git a/cabal-testsuite/src/Test/Cabal/Run.hs b/cabal-testsuite/src/Test/Cabal/Run.hs
index 37b27e9edf3..498c14ded23 100644
--- a/cabal-testsuite/src/Test/Cabal/Run.hs
+++ b/cabal-testsuite/src/Test/Cabal/Run.hs
@@ -54,6 +54,29 @@ runAction _verbosity mb_cwd env_overrides path0 args input action = do
     mb_env <- getEffectiveEnvironment env_overrides
     putStrLn $ "+ " ++ showCommandForUser path args
     (readh, writeh) <- createPipe
+
+    -- `System.Process.createPipe` calls (through many intermediaries)
+    -- `GHC.IO.Handle.FD.fdToHandle`, whose documentation says:
+    --
+    -- > Makes a binary Handle. This is for historical reasons; it should
+    -- > probably be a text Handle with the default encoding and newline
+    -- > translation instead.
+    --
+    -- The documentation for `System.IO.hSetBinaryMode` says:
+    --
+    -- > This has the same effect as calling `hSetEncoding` with `char8`, together
+    -- > with `hSetNewlineMode` with `noNewlineTranslation`.
+    --
+    -- But this is a lie, and Unicode written to or read from binary handles is
+    -- always encoded or decoded as Latin-1, which is always the wrong choice.
+    --
+    -- Therefore, we explicitly set the output to UTF-8 to keep it consistent
+    -- between platforms and correct on all modern computers.
+    --
+    -- See: https://gitlab.haskell.org/ghc/ghc/-/issues/25307
+    hSetEncoding readh utf8
+    hSetEncoding writeh utf8
+
     hSetBuffering readh LineBuffering
     hSetBuffering writeh LineBuffering
     let drain = do
diff --git a/cabal-validate/README.md b/cabal-validate/README.md
new file mode 100644
index 00000000000..5f40e9d28f1
--- /dev/null
+++ b/cabal-validate/README.md
@@ -0,0 +1,23 @@
+# cabal-validate
+
+`cabal-validate` is a script that builds and tests `Cabal` and `cabal-install`.
+`cabal-validate` can be run with `validate.sh` in the repository root;
+arguments passed to `validate.sh` will be forwarded to `cabal-validate`.
+
+Notable arguments include:
+
+- `-v`/`--verbose` to display build and test output in real-time, instead of
+  only if commands fail.
+- `-s`/`--step` to run a specific step (e.g. `-s build -s lib-tests` will only
+  run the `build` and `lib-tests` steps).
+- `-p`/`--pattern` to filter tests by a pattern.
+
+## Hacking on cabal-validate
+
+Overview of important modules:
+
+- `Main.hs` encodes all the commands that are run for each step.
+- `Cli.hs` parses the CLI arguments and resolves default values from the
+  environment, like determining which steps are run by default or the `--jobs`
+  argument to pass to test suites.
+- `Step.hs` lists the available steps.
diff --git a/cabal-validate/cabal-validate.cabal b/cabal-validate/cabal-validate.cabal
new file mode 100644
index 00000000000..582cf67434a
--- /dev/null
+++ b/cabal-validate/cabal-validate.cabal
@@ -0,0 +1,47 @@
+cabal-version: 3.0
+name:          cabal-validate
+version:       1.0.0
+copyright:     2024-2024, Cabal Development Team (see AUTHORS file)
+license:       BSD-3-Clause
+author:        Cabal Development Team <cabal-devel@haskell.org>
+synopsis:      An internal tool for building and testing the Cabal package manager
+build-type:    Simple
+
+common common
+    ghc-options: -Wall
+
+    if impl(ghc <9.6)
+        -- Pattern exhaustiveness checker is not as good, misses a case.
+        ghc-options: -Wno-incomplete-patterns
+
+    default-language: Haskell2010
+    default-extensions:
+        OverloadedStrings
+        , TypeApplications
+
+executable cabal-validate
+    import: common
+    ghc-options: -O -threaded -rtsopts -with-rtsopts=-N
+
+    main-is: Main.hs
+    hs-source-dirs: src
+
+    other-modules:
+        , ANSI
+        , Cli
+        , ClockUtil
+        , OutputUtil
+        , ProcessUtil
+        , Step
+
+    build-depends:
+        , base >=4 && <5
+        , bytestring >=0.11 && <1
+        , containers >=0.6 && <1
+        , directory >=1.0 && <2
+        , filepath >=1 && <2
+        , optparse-applicative >=0.18 && <1
+        , terminal-size >=0.3 && <1
+        , text >=2 && <3
+        , time >=1 && <2
+        , typed-process >=0.2 && <1
diff --git a/cabal-validate/src/ANSI.hs b/cabal-validate/src/ANSI.hs
new file mode 100644
index 00000000000..a0d9111d957
--- /dev/null
+++ b/cabal-validate/src/ANSI.hs
@@ -0,0 +1,105 @@
+-- | ANSI escape sequences.
+--
+-- This is a stripped-down version of the parts of the @ansi-terminal@ package
+-- we use.
+--
+-- See: <https://gist.github.com/fnky/458719343aabd01cfb17a3a4f7296797>
+module ANSI
+  ( SGR (..)
+  , setSGR
+  ) where
+
+-- | Render a single numeric SGR sequence.
+rawSGR :: Int -> String
+rawSGR code = "\x1b[" <> show code <> "m"
+
+-- | Render a series of `SGR` escape sequences.
+setSGR :: [SGR] -> String
+setSGR = concat . map renderSGR
+
+-- | All of the SGR sequences we want to use.
+data SGR
+  = Reset
+  | Bold
+  | Dim
+  | Italic
+  | Underline
+  | Black
+  | Red
+  | Green
+  | Yellow
+  | Blue
+  | Magenta
+  | Cyan
+  | White
+  | Default
+  | OnBlack
+  | OnRed
+  | OnGreen
+  | OnYellow
+  | OnBlue
+  | OnMagenta
+  | OnCyan
+  | OnWhite
+  | OnDefault
+  | BrightBlack
+  | BrightRed
+  | BrightGreen
+  | BrightYellow
+  | BrightBlue
+  | BrightMagenta
+  | BrightCyan
+  | BrightWhite
+  | OnBrightBlack
+  | OnBrightRed
+  | OnBrightGreen
+  | OnBrightYellow
+  | OnBrightBlue
+  | OnBrightMagenta
+  | OnBrightCyan
+  | OnBrightWhite
+  deriving (Show)
+
+-- Render a single `SGR` sequence.
+renderSGR :: SGR -> String
+renderSGR code =
+  case code of
+    Reset -> rawSGR 0
+    Bold -> rawSGR 1
+    Dim -> rawSGR 2
+    Italic -> rawSGR 3
+    Underline -> rawSGR 4
+    Black -> rawSGR 30
+    Red -> rawSGR 31
+    Green -> rawSGR 32
+    Yellow -> rawSGR 33
+    Blue -> rawSGR 34
+    Magenta -> rawSGR 35
+    Cyan -> rawSGR 36
+    White -> rawSGR 37
+    Default -> rawSGR 39
+    OnBlack -> rawSGR 40
+    OnRed -> rawSGR 41
+    OnGreen -> rawSGR 42
+    OnYellow -> rawSGR 43
+    OnBlue -> rawSGR 44
+    OnMagenta -> rawSGR 45
+    OnCyan -> rawSGR 46
+    OnWhite -> rawSGR 47
+    OnDefault -> rawSGR 49
+    BrightBlack -> rawSGR 90
+    BrightRed -> rawSGR 91
+    BrightGreen -> rawSGR 92
+    BrightYellow -> rawSGR 93
+    BrightBlue -> rawSGR 94
+    BrightMagenta -> rawSGR 95
+    BrightCyan -> rawSGR 96
+    BrightWhite -> rawSGR 97
+    OnBrightBlack -> rawSGR 100
+    OnBrightRed -> rawSGR 101
+    OnBrightGreen -> rawSGR 102
+    OnBrightYellow -> rawSGR 103
+    OnBrightBlue -> rawSGR 104
+    OnBrightMagenta -> rawSGR 105
+    OnBrightCyan -> rawSGR 106
+    OnBrightWhite -> rawSGR 107
diff --git a/cabal-validate/src/Cli.hs b/cabal-validate/src/Cli.hs
new file mode 100644
index 00000000000..ef01d907594
--- /dev/null
+++ b/cabal-validate/src/Cli.hs
@@ -0,0 +1,437 @@
+-- | Parse CLI arguments and resolve defaults from the environment.
+module Cli
+  ( Opts (..)
+  , parseOpts
+  , HackageTests (..)
+  , Compiler (..)
+  , VersionParseException (..)
+  )
+where
+
+import Control.Applicative (Alternative (many, (<|>)), (<**>))
+import Control.Exception (Exception (displayException), throw)
+import Control.Monad (forM_, when)
+import Data.Data (Typeable)
+import Data.Maybe (listToMaybe)
+import qualified Data.Text as T
+import qualified Data.Text.Lazy as T (toStrict)
+import qualified Data.Text.Lazy.Encoding as T (decodeUtf8)
+import Data.Version (Version, parseVersion)
+import GHC.Conc (getNumCapabilities)
+import Options.Applicative
+  ( FlagFields
+  , Mod
+  , Parser
+  , ParserInfo
+  , auto
+  , execParser
+  , flag
+  , flag'
+  , fullDesc
+  , help
+  , helper
+  , hidden
+  , info
+  , long
+  , maybeReader
+  , option
+  , progDesc
+  , short
+  , strOption
+  , switch
+  , value
+  )
+import qualified Options.Applicative as Opt
+import System.Directory (getCurrentDirectory)
+import System.Exit (exitSuccess)
+import System.Info (arch, os)
+import System.Process.Typed (proc, readProcessStdout_)
+import Text.ParserCombinators.ReadP (readP_to_S)
+
+import ClockUtil (AbsoluteTime, getAbsoluteTime)
+import Step (Step (..), displayStep, parseStep)
+
+-- | Command-line options, resolved with context from the environment.
+data Opts = Opts
+  { verbose :: Bool
+  -- ^ Whether to display build and test output.
+  , jobs :: Int
+  -- ^ How many jobs to use when running tests.
+  --
+  -- Defaults to the number of physical cores.
+  , cwd :: FilePath
+  -- ^ Current working directory when @cabal-validate@ was started.
+  , startTime :: AbsoluteTime
+  -- ^ System time when @cabal-validate@ was started.
+  --
+  -- Used to determine the total test duration so far.
+  , compiler :: Compiler
+  -- ^ Compiler to build Cabal with.
+  --
+  -- Defaults to @ghc@.
+  , extraCompilers :: [FilePath]
+  -- ^ Extra compilers to run @cabal-testsuite@ with.
+  , cabal :: FilePath
+  -- ^ @cabal-install@ to build Cabal with.
+  --
+  -- Defaults to @cabal@.
+  , hackageTests :: HackageTests
+  -- ^ Whether to run tests on Hackage data, and if so how much.
+  --
+  -- Defaults to `NoHackageTests`.
+  , archPath :: FilePath
+  -- ^ The path for this system's architecture within the build directory.
+  --
+  -- Like @x86_64-windows@ or @aarch64-osx@ or @arm-linux@.
+  , projectFile :: FilePath
+  -- ^ Path to the @cabal.project@ file to use for running tests.
+  , tastyArgs :: [String]
+  -- ^ Extra arguments to pass to @tasty@ test suites.
+  --
+  -- This defaults to @--hide-successes@ (which cannot yet be changed) and
+  -- includes the @--pattern@ argument if one is given.
+  , targets :: [String]
+  -- ^ Targets to build.
+  , steps :: [Step]
+  -- ^ Steps to run.
+  }
+  deriving (Show)
+
+-- | Whether to run tests on Hackage data, and if so how much.
+data HackageTests
+  = -- | Run tests on complete Hackage data.
+    CompleteHackageTests
+  | -- | Run tests on partial Hackage data.
+    PartialHackageTests
+  | -- | Do not run tests on Hackage data.
+    NoHackageTests
+  deriving (Show)
+
+-- | A compiler executable and version number.
+data Compiler = Compiler
+  { compilerExecutable :: FilePath
+  -- ^ The compiler's executable.
+  , compilerVersion :: Version
+  -- ^ The compiler's version number.
+  }
+  deriving (Show)
+
+-- | An `Exception` thrown when parsing @--numeric-version@ output from a compiler.
+data VersionParseException = VersionParseException
+  { versionInput :: String
+  -- ^ The string we attempted to parse.
+  , versionExecutable :: FilePath
+  -- ^ The compiler which produced the string.
+  }
+  deriving (Typeable, Show)
+
+instance Exception VersionParseException where
+  displayException exception =
+    "Failed to parse `"
+      <> versionExecutable exception
+      <> " --numeric-version` output: "
+      <> show (versionInput exception)
+
+-- | Runs @ghc --numeric-version@ for the given executable to construct a
+-- `Compiler`.
+makeCompiler :: FilePath -> IO Compiler
+makeCompiler executable = do
+  stdout <-
+    readProcessStdout_ $
+      proc executable ["--numeric-version"]
+  let version = T.unpack $ T.strip $ T.toStrict $ T.decodeUtf8 stdout
+      parsedVersions = readP_to_S parseVersion version
+      -- Who needs error messages? Those aren't in the API.
+      maybeParsedVersion =
+        listToMaybe
+          [ parsed
+          | (parsed, []) <- parsedVersions
+          ]
+      parsedVersion = case maybeParsedVersion of
+        Just parsedVersion' -> parsedVersion'
+        Nothing ->
+          throw
+            VersionParseException
+              { versionInput = version
+              , versionExecutable = executable
+              }
+
+  pure
+    Compiler
+      { compilerExecutable = executable
+      , compilerVersion = parsedVersion
+      }
+
+-- | Resolve options and default values from the environment.
+--
+-- This makes the `Opts` type much nicer to deal with than `RawOpts`.
+resolveOpts :: RawOpts -> IO Opts
+resolveOpts opts = do
+  let optionals :: Bool -> [a] -> [a]
+      optionals True items = items
+      optionals False _ = []
+
+      optional :: Bool -> a -> [a]
+      optional keep item = optionals keep [item]
+
+      steps' =
+        if not (null (rawSteps opts))
+          then rawSteps opts
+          else
+            concat
+              [
+                [ PrintConfig
+                , PrintToolVersions
+                , Build
+                ]
+              , optional (rawDoctest opts) Doctest
+              , optional (rawRunLibTests opts) LibTests
+              , optional (rawRunLibSuite opts) LibSuite
+              , optional (rawRunLibSuite opts && not (null (rawExtraCompilers opts))) LibSuiteExtras
+              , optional (rawRunCliTests opts && not (rawLibOnly opts)) CliTests
+              , optional (rawRunCliSuite opts && not (rawLibOnly opts)) CliSuite
+              , optionals (rawSolverBenchmarks opts) [SolverBenchmarksTests, SolverBenchmarksRun]
+              , [TimeSummary]
+              ]
+
+      targets' =
+        concat
+          [
+            [ "Cabal"
+            , "Cabal-hooks"
+            , "cabal-testsuite"
+            , "Cabal-tests"
+            , "Cabal-QuickCheck"
+            , "Cabal-tree-diff"
+            , "Cabal-described"
+            ]
+          , optionals
+              (not (rawLibOnly opts))
+              [ "cabal-install"
+              , "cabal-install-solver"
+              , "cabal-benchmarks"
+              ]
+          , optionals
+              (rawSolverBenchmarks opts)
+              [ "solver-benchmarks"
+              , "solver-benchmarks:tests"
+              ]
+          ]
+
+      archPath' =
+        let osPath =
+              case os of
+                "darwin" -> "osx"
+                "linux" -> "linux"
+                "mingw32" -> "windows"
+                _ -> os -- TODO: Warning?
+         in arch <> "-" <> osPath
+
+      projectFile' =
+        if rawLibOnly opts
+          then "cabal.validate-libonly.project"
+          else "cabal.validate.project"
+
+      tastyArgs' =
+        "--hide-successes"
+          : case rawTastyPattern opts of
+            Just tastyPattern -> ["--pattern", tastyPattern]
+            Nothing -> []
+
+  when (rawListSteps opts) $ do
+    -- TODO: This should probably list _all_ available steps, not just the selected ones!
+    putStrLn "Targets:"
+    forM_ targets' $ \target -> do
+      putStrLn $ "  " <> target
+    putStrLn "Steps:"
+    forM_ steps' $ \step -> do
+      putStrLn $ "  " <> displayStep step
+    exitSuccess
+
+  startTime' <- getAbsoluteTime
+  jobs' <- maybe getNumCapabilities pure (rawJobs opts)
+  cwd' <- getCurrentDirectory
+  compiler' <- makeCompiler (rawCompiler opts)
+
+  pure
+    Opts
+      { verbose = rawVerbose opts
+      , jobs = jobs'
+      , cwd = cwd'
+      , startTime = startTime'
+      , compiler = compiler'
+      , extraCompilers = rawExtraCompilers opts
+      , cabal = rawCabal opts
+      , archPath = archPath'
+      , projectFile = projectFile'
+      , hackageTests = rawHackageTests opts
+      , tastyArgs = tastyArgs'
+      , targets = targets'
+      , steps = steps'
+      }
+
+-- | Literate command-line options as supplied by the user, before resolving
+-- defaults and other values from the environment.
+data RawOpts = RawOpts
+  { rawVerbose :: Bool
+  , rawJobs :: Maybe Int
+  , rawCompiler :: FilePath
+  , rawCabal :: FilePath
+  , rawExtraCompilers :: [FilePath]
+  , rawTastyPattern :: Maybe String
+  , rawDoctest :: Bool
+  , rawSteps :: [Step]
+  , rawListSteps :: Bool
+  , rawLibOnly :: Bool
+  , rawRunLibTests :: Bool
+  , rawRunCliTests :: Bool
+  , rawRunLibSuite :: Bool
+  , rawRunCliSuite :: Bool
+  , rawSolverBenchmarks :: Bool
+  , rawHackageTests :: HackageTests
+  }
+  deriving (Show)
+
+-- | `Parser` for `RawOpts`.
+--
+-- See: `fullRawOptsParser`
+rawOptsParser :: Parser RawOpts
+rawOptsParser =
+  RawOpts
+    <$> ( flag'
+            True
+            ( short 'v'
+                <> long "verbose"
+                <> help "Always display build and test output"
+            )
+            <|> flag
+              False
+              False
+              ( short 'q'
+                  <> long "quiet"
+                  <> help "Silence build and test output"
+              )
+        )
+    <*> option
+      (Just <$> auto)
+      ( short 'j'
+          <> long "jobs"
+          <> help "Passed to `cabal build --jobs`"
+          <> value Nothing
+      )
+    <*> strOption
+      ( short 'w'
+          <> long "with-compiler"
+          <> help "Build Cabal with the given compiler instead of `ghc`"
+          <> value "ghc"
+      )
+    <*> strOption
+      ( long "with-cabal"
+          <> help "Test the given `cabal-install` (the `cabal` on your `$PATH` is used for builds)"
+          <> value "cabal"
+      )
+    <*> many
+      ( strOption
+          ( long "extra-hc"
+              <> help "Extra compilers to run the test suites against"
+          )
+      )
+    <*> option
+      (Just <$> Opt.str)
+      ( short 'p'
+          <> long "pattern"
+          <> help "Pattern to filter tests by"
+          <> value Nothing
+      )
+    <*> boolOption
+      False
+      "doctest"
+      ( help "Run doctest on the `Cabal` library"
+      )
+    <*> many
+      ( option
+          (maybeReader parseStep)
+          ( short 's'
+              <> long "step"
+              <> help "Run only a specific step (can be specified multiple times)"
+          )
+      )
+    <*> switch
+      ( long "list-steps"
+          <> help "List the available steps and exit"
+      )
+    <*> ( flag'
+            True
+            ( long "lib-only"
+                <> help "Test only `Cabal` (the library)"
+            )
+            <|> flag
+              False
+              False
+              ( long "cli"
+                  <> help "Test `cabal-install` (the executable) in addition to `Cabal` (the library)"
+              )
+        )
+    <*> boolOption
+      True
+      "run-lib-tests"
+      ( help "Run tests for the `Cabal` library"
+      )
+    <*> boolOption
+      True
+      "run-cli-tests"
+      ( help "Run client tests for the `cabal-install` executable"
+      )
+    <*> boolOption
+      False
+      "run-lib-suite"
+      ( help "Run `cabal-testsuite` with the `Cabal` library"
+      )
+    <*> boolOption
+      False
+      "run-cli-suite"
+      ( help "Run `cabal-testsuite` with the `cabal-install` executable"
+      )
+    <*> boolOption
+      False
+      "solver-benchmarks"
+      ( help "Build and trial run `solver-benchmarks`"
+      )
+    <*> ( flag'
+            CompleteHackageTests
+            ( long "complete-hackage-tests"
+                <> help "Run `hackage-tests` on complete Hackage data"
+            )
+            <|> flag
+              NoHackageTests
+              PartialHackageTests
+              ( long "partial-hackage-tests"
+                  <> help "Run `hackage-tests` on parts of Hackage data"
+              )
+        )
+
+-- | Parse a boolean switch with separate names for the true and false options.
+boolOption' :: Bool -> String -> String -> Mod FlagFields Bool -> Parser Bool
+boolOption' defaultValue trueName falseName modifiers =
+  flag' True (modifiers <> long trueName)
+    <|> flag defaultValue False (modifiers <> hidden <> long falseName)
+
+-- | Parse a boolean switch with a @--no-*@ flag for setting the option to false.
+boolOption :: Bool -> String -> Mod FlagFields Bool -> Parser Bool
+boolOption defaultValue trueName =
+  boolOption' defaultValue trueName ("no-" <> trueName)
+
+-- | Full `Parser` for `RawOpts`, which includes a @--help@ argument and
+-- information about the program.
+fullRawOptsParser :: ParserInfo RawOpts
+fullRawOptsParser =
+  info
+    (rawOptsParser <**> helper)
+    ( fullDesc
+        <> progDesc "Test suite runner for `Cabal` and `cabal-install` developers"
+    )
+
+-- | Parse command-line arguments and resolve defaults from the environment,
+-- producing `Opts`.
+parseOpts :: IO Opts
+parseOpts = execParser fullRawOptsParser >>= resolveOpts
diff --git a/cabal-validate/src/ClockUtil.hs b/cabal-validate/src/ClockUtil.hs
new file mode 100644
index 00000000000..2df7cdd9866
--- /dev/null
+++ b/cabal-validate/src/ClockUtil.hs
@@ -0,0 +1,33 @@
+-- | Utilities for dealing with times and durations.
+module ClockUtil
+  ( DiffTime
+  , AbsoluteTime
+  , diffAbsoluteTime
+  , getAbsoluteTime
+  , formatDiffTime
+  ) where
+
+import Data.Time.Clock (DiffTime, secondsToDiffTime)
+import Data.Time.Clock.System (getSystemTime, systemToTAITime)
+import Data.Time.Clock.TAI (AbsoluteTime, diffAbsoluteTime)
+import Data.Time.Format (defaultTimeLocale, formatTime)
+
+-- | Get the current time as an `AbsoluteTime`.
+getAbsoluteTime :: IO AbsoluteTime
+getAbsoluteTime = systemToTAITime <$> getSystemTime
+
+-- | Format a `DiffTime` nicely.
+--
+-- Short durations are formatted like @16.34s@, durations longer than a minute
+-- are formatted like @22:34.68@, durations longer than an hour are formatted
+-- like @1:32:04.68@.
+formatDiffTime :: DiffTime -> String
+formatDiffTime delta =
+  let minute = secondsToDiffTime 60
+      hour = 60 * minute
+   in if delta >= hour
+        then formatTime defaultTimeLocale "%h:%02M:%02ES" delta
+        else
+          if delta >= minute
+            then formatTime defaultTimeLocale "%m:%2ES" delta
+            else formatTime defaultTimeLocale "%2Ess" delta
diff --git a/cabal-validate/src/Main.hs b/cabal-validate/src/Main.hs
new file mode 100644
index 00000000000..428a8a7358d
--- /dev/null
+++ b/cabal-validate/src/Main.hs
@@ -0,0 +1,425 @@
+-- | Entry-point to the @cabal-validate@ script.
+--
+-- This module encodes all the commands that are run for each step in
+-- `runStep`.
+module Main
+  ( main
+  , runStep
+  ) where
+
+import Control.Monad (forM_)
+import qualified Data.Text as T
+import qualified Data.Text.IO as T
+import qualified Data.Text.Lazy as T (toStrict)
+import qualified Data.Text.Lazy.Encoding as T (decodeUtf8)
+import Data.Version (makeVersion, showVersion)
+import System.FilePath ((</>))
+import System.Process.Typed (proc, readProcessStdout_)
+
+import ANSI (SGR (Bold, BrightCyan, Reset), setSGR)
+import Cli (Compiler (..), HackageTests (..), Opts (..), parseOpts)
+import ClockUtil (diffAbsoluteTime, formatDiffTime, getAbsoluteTime)
+import OutputUtil (printHeader, withTiming)
+import ProcessUtil (timed, timedWithCwd)
+import Step (Step (..), displayStep)
+
+-- | Entry-point for @cabal-validate@.
+main :: IO ()
+main = do
+  opts <- parseOpts
+  forM_ (steps opts) $ \step -> do
+    runStep opts step
+
+-- | Run a given `Step` with the given `Opts`.
+runStep :: Opts -> Step -> IO ()
+runStep opts step = do
+  let title = displayStep step
+  printHeader title
+  let action = case step of
+        PrintConfig -> printConfig opts
+        PrintToolVersions -> printToolVersions opts
+        Build -> build opts
+        Doctest -> doctest opts
+        LibTests -> libTests opts
+        LibSuite -> libSuite opts
+        LibSuiteExtras -> libSuiteExtras opts
+        CliSuite -> cliSuite opts
+        CliTests -> cliTests opts
+        SolverBenchmarksTests -> solverBenchmarksTests opts
+        SolverBenchmarksRun -> solverBenchmarksRun opts
+        TimeSummary -> timeSummary opts
+  withTiming (startTime opts) title action
+  T.putStrLn ""
+
+-- | Compiler with version number like @ghc-9.6.6@.
+baseHc :: Opts -> FilePath
+baseHc opts = "ghc-" <> showVersion (compilerVersion $ compiler opts)
+
+-- | Base build directory for @cabal-validate@.
+baseBuildDir :: Opts -> FilePath
+baseBuildDir opts = "dist-newstyle-validate-" <> baseHc opts
+
+-- | Absolute path to the build directory for this architecture.
+--
+-- This is a path nested fairly deeply under `baseBuildDir`.
+buildDir :: Opts -> FilePath
+buildDir opts =
+  cwd opts
+    </> baseBuildDir opts
+    </> "build"
+    </> archPath opts
+    </> baseHc opts
+
+-- | @--num-threads@ argument for test suites.
+--
+-- This isn't always used because some test suites are finicky and only accept
+-- @-j@.
+jobsArgs :: Opts -> [String]
+jobsArgs opts = ["--num-threads", show $ jobs opts]
+
+-- | Default arguments for invoking @cabal@.
+cabalArgs :: Opts -> [String]
+cabalArgs opts =
+  [ "--jobs=" <> show (jobs opts)
+  , "--with-compiler=" <> compilerExecutable (compiler opts)
+  , "--builddir=" <> baseBuildDir opts
+  , "--project-file=" <> projectFile opts
+  ]
+
+-- | The `buildDir` for @cabal-testsuite-3@.
+cabalTestsuiteBuildDir :: Opts -> FilePath
+cabalTestsuiteBuildDir opts =
+  buildDir opts
+    </> "cabal-testsuite-3"
+
+-- | Arguments for @cabal build@.
+cabalNewBuildArgs :: Opts -> [String]
+cabalNewBuildArgs opts = "build" : cabalArgs opts
+
+-- | Arguments for @cabal list-bin@.
+--
+-- This is used to find the binaries for various test suites.
+cabalListBinArgs :: Opts -> [String]
+cabalListBinArgs opts = "list-bin" : cabalArgs opts
+
+-- | Get the binary for a given @cabal@ target by running @cabal list-bin@.
+cabalListBin :: Opts -> String -> IO FilePath
+cabalListBin opts target = do
+  let args = cabalListBinArgs opts ++ [target]
+  stdout <-
+    readProcessStdout_ $
+      proc (cabal opts) args
+
+  pure (T.unpack $ T.strip $ T.toStrict $ T.decodeUtf8 stdout)
+
+-- | Get the RTS arguments for invoking test suites.
+--
+-- These seem to only be used for some of the test suites, I'm not sure why.
+rtsArgs :: Opts -> [String]
+rtsArgs opts =
+  case archPath opts of
+    "x86_64-windows" ->
+      -- See: https://github.com/haskell/cabal/issues/9571
+      if compilerVersion (compiler opts) > makeVersion [9, 0, 2]
+        then ["+RTS", "--io-manager=native", "-RTS"]
+        else []
+    _ -> []
+
+-- | Run a binary built by @cabal@ and output timing information.
+--
+-- This is used to run many of the test suites.
+timedCabalBin :: Opts -> String -> String -> [String] -> IO ()
+timedCabalBin opts package component args = do
+  command <- cabalListBin opts (package <> ":" <> component)
+  timedWithCwd
+    opts
+    package
+    command
+    args
+
+-- | Print the configuration for CI logs.
+printConfig :: Opts -> IO ()
+printConfig opts = do
+  putStr $
+    unlines
+      [ "compiler:          "
+          <> compilerExecutable (compiler opts)
+      , "cabal-install:     "
+          <> cabal opts
+      , "jobs:              "
+          <> show (jobs opts)
+      , "steps:             "
+          <> unwords (map displayStep (steps opts))
+      , "Hackage tests:     "
+          <> show (hackageTests opts)
+      , "verbose:           "
+          <> show (verbose opts)
+      , "extra compilers:   "
+          <> unwords (extraCompilers opts)
+      , "extra RTS options: "
+          <> unwords (rtsArgs opts)
+      ]
+
+-- | Print the versions of tools being used.
+printToolVersions :: Opts -> IO ()
+printToolVersions opts = do
+  timed opts (compilerExecutable (compiler opts)) ["--version"]
+  timed opts (cabal opts) ["--version"]
+
+  forM_ (extraCompilers opts) $ \compiler' -> do
+    timed opts compiler' ["--version"]
+
+-- | Run the build step.
+build :: Opts -> IO ()
+build opts = do
+  printHeader "build (dry run)"
+  timed
+    opts
+    (cabal opts)
+    ( cabalNewBuildArgs opts
+        ++ targets opts
+        ++ ["--dry-run"]
+    )
+
+  printHeader "build (full build plan; cached and to-be-built dependencies)"
+  timed
+    opts
+    "jq"
+    [ "-r"
+    , -- TODO: Maybe use `cabal-plan`? It's a heavy dependency though...
+      ".\"install-plan\" | map(.\"pkg-name\" + \"-\" + .\"pkg-version\" + \" \" + .\"component-name\") | join(\"\n\")"
+    , baseBuildDir opts </> "cache" </> "plan.json"
+    ]
+
+  printHeader "build (actual build)"
+  timed
+    opts
+    (cabal opts)
+    (cabalNewBuildArgs opts ++ targets opts)
+
+-- | Run doctests.
+--
+-- This doesn't work on my machine, maybe @cabal.nix@ needs some love to
+-- support @cabal-env@?
+doctest :: Opts -> IO ()
+doctest opts = do
+  timed
+    opts
+    "cabal-env"
+    [ "--name"
+    , "doctest-cabal"
+    , "--transitive"
+    , "QuickCheck"
+    ]
+
+  timed
+    opts
+    "cabal-env"
+    [ "--name"
+    , "doctest-cabal"
+    , "array"
+    , "bytestring"
+    , "containers"
+    , "deepseq"
+    , "directory"
+    , "filepath"
+    , "pretty"
+    , "process"
+    , "time"
+    , "binary"
+    , "unix"
+    , "text"
+    , "parsec"
+    , "mtl"
+    ]
+
+  timed
+    opts
+    "doctest"
+    [ "-package-env=doctest-Cabal"
+    , "--fast"
+    , "Cabal/Distribution"
+    , "Cabal/Language"
+    ]
+
+-- | Run tests for the @Cabal@ library, and also `runHackageTests` if those are
+-- enabled.
+libTests :: Opts -> IO ()
+libTests opts = do
+  let runCabalTests' suite extraArgs =
+        timedCabalBin
+          opts
+          "Cabal-tests"
+          ("test:" <> suite)
+          ( tastyArgs opts
+              ++ jobsArgs opts
+              ++ extraArgs
+          )
+
+      runCabalTests suite = runCabalTests' suite []
+
+  runCabalTests' "unit-tests" ["--with-ghc=" <> compilerExecutable (compiler opts)]
+  runCabalTests "check-tests"
+  runCabalTests "parser-tests"
+  runCabalTests "rpmvercmp"
+  runCabalTests "no-thunks-test"
+
+  runHackageTests opts
+
+-- | Run Hackage tests, if enabled.
+runHackageTests :: Opts -> IO ()
+runHackageTests opts
+  | NoHackageTests <- hackageTests opts = pure ()
+  | otherwise = do
+      command <- cabalListBin opts "Cabal-tests:test:hackage-tests"
+
+      let
+        -- See #10284 for why this value is pinned.
+        hackageTestsIndexState = "--index-state=2024-08-25"
+
+        hackageTest args =
+          timedWithCwd
+            opts
+            "Cabal-tests"
+            command
+            (args ++ [hackageTestsIndexState])
+
+      hackageTest ["read-fields"]
+
+      case hackageTests opts of
+        CompleteHackageTests -> do
+          hackageTest ["parsec"]
+          hackageTest ["roundtrip"]
+        PartialHackageTests -> do
+          hackageTest ["parsec", "d"]
+          hackageTest ["roundtrip", "k"]
+
+-- | Run @cabal-testsuite@ with the @Cabal@ library with a non-default GHC.
+libSuiteWith :: Opts -> FilePath -> [String] -> IO ()
+libSuiteWith opts ghc extraArgs =
+  timedCabalBin
+    opts
+    "cabal-testsuite"
+    "exe:cabal-tests"
+    ( [ "--builddir=" <> cabalTestsuiteBuildDir opts
+      , "--with-ghc=" <> ghc
+      , -- This test suite doesn't support `--jobs` _or_ `--num-threads`!
+        "-j" <> show (jobs opts)
+      ]
+        ++ tastyArgs opts
+        ++ extraArgs
+    )
+
+-- | Run @cabal-testsuite@ with the @Cabal@ library with the default GHC.
+libSuite :: Opts -> IO ()
+libSuite opts = libSuiteWith opts (compilerExecutable (compiler opts)) (rtsArgs opts)
+
+-- | Run @cabal-testsuite@ with the @Cabal@ library with all extra GHCs.
+libSuiteExtras :: Opts -> IO ()
+libSuiteExtras opts = forM_ (extraCompilers opts) $ \compiler' ->
+  libSuiteWith opts compiler' []
+
+-- | Test the @cabal-install@ executable.
+--
+-- These tests mostly run sequentially, so they're pretty slow as a result.
+cliTests :: Opts -> IO ()
+cliTests opts = do
+  -- These are sorted in asc time used, quicker tests first.
+  timedCabalBin
+    opts
+    "cabal-install"
+    "test:long-tests"
+    ( jobsArgs opts
+        ++ tastyArgs opts
+    )
+
+  -- This doesn't work in parallel either.
+  timedCabalBin
+    opts
+    "cabal-install"
+    "test:unit-tests"
+    ( ["--num-threads", "1"]
+        ++ tastyArgs opts
+    )
+
+  -- Only single job, otherwise we fail with "Heap exhausted"
+  timedCabalBin
+    opts
+    "cabal-install"
+    "test:mem-use-tests"
+    ( ["--num-threads", "1"]
+        ++ tastyArgs opts
+    )
+
+  -- This test-suite doesn't like concurrency
+  timedCabalBin
+    opts
+    "cabal-install"
+    "test:integration-tests2"
+    ( [ "--num-threads"
+      , "1"
+      , "--with-ghc=" <> compilerExecutable (compiler opts)
+      ]
+        ++ tastyArgs opts
+    )
+
+-- | Run @cabal-testsuite@ with the @cabal-install@ executable.
+cliSuite :: Opts -> IO ()
+cliSuite opts = do
+  cabal' <- cabalListBin opts "cabal-install:exe:cabal"
+
+  timedCabalBin
+    opts
+    "cabal-testsuite"
+    "exe:cabal-tests"
+    ( [ "--builddir=" <> cabalTestsuiteBuildDir opts
+      , "--with-cabal=" <> cabal'
+      , "--with-ghc=" <> compilerExecutable (compiler opts)
+      , "--intree-cabal-lib=" <> cwd opts
+      , "--test-tmp=" <> cwd opts </> "testdb"
+      , -- This test suite doesn't support `--jobs` _or_ `--num-threads`!
+        "-j"
+      , show (jobs opts)
+      ]
+        ++ tastyArgs opts
+        ++ rtsArgs opts
+    )
+
+-- | Run the @solver-benchmarks@ unit tests.
+solverBenchmarksTests :: Opts -> IO ()
+solverBenchmarksTests opts = do
+  command <- cabalListBin opts "solver-benchmarks:test:unit-tests"
+
+  timedWithCwd
+    opts
+    "Cabal"
+    command
+    []
+
+-- | Run the @solver-benchmarks@.
+solverBenchmarksRun :: Opts -> IO ()
+solverBenchmarksRun opts = do
+  command <- cabalListBin opts "solver-benchmarks:exe:hackage-benchmark"
+  cabal' <- cabalListBin opts "cabal-install:exe:cabal"
+
+  timedWithCwd
+    opts
+    "Cabal"
+    command
+    [ "--cabal1=" <> cabal opts
+    , "--cabal2=" <> cabal'
+    , "--trials=5"
+    , "--packages=Chart-diagrams"
+    , "--print-trials"
+    ]
+
+-- | Print the total time taken so far.
+timeSummary :: Opts -> IO ()
+timeSummary opts = do
+  endTime <- getAbsoluteTime
+  let totalDuration = diffAbsoluteTime endTime (startTime opts)
+  putStrLn $
+    setSGR [Bold, BrightCyan]
+      <> "!!! Validation completed in "
+      <> formatDiffTime totalDuration
+      <> setSGR [Reset]
diff --git a/cabal-validate/src/OutputUtil.hs b/cabal-validate/src/OutputUtil.hs
new file mode 100644
index 00000000000..576c6180433
--- /dev/null
+++ b/cabal-validate/src/OutputUtil.hs
@@ -0,0 +1,86 @@
+-- | Utilities for printing terminal output.
+module OutputUtil
+  ( printHeader
+  , withTiming
+  ) where
+
+import Control.Exception (catch)
+import qualified System.Console.Terminal.Size as Terminal
+import System.Process.Typed (ExitCodeException)
+
+import ANSI (SGR (Bold, BrightCyan, BrightGreen, BrightRed, Reset), setSGR)
+import ClockUtil (AbsoluteTime, diffAbsoluteTime, formatDiffTime, getAbsoluteTime)
+import System.Exit (exitFailure)
+
+-- | Get the width of the current terminal, or 80 if no width can be determined.
+getTerminalWidth :: IO Int
+getTerminalWidth = maybe 80 Terminal.width <$> Terminal.size @Int
+
+-- | Print a header for a given step.
+--
+-- This is colorful and hard to miss in the output.
+printHeader
+  :: String
+  -- ^ Title to print.
+  -> IO ()
+printHeader title = do
+  columns <- getTerminalWidth
+  let left = 3
+      right = columns - length title - left - 2
+      header =
+        setSGR [Bold, BrightCyan]
+          <> replicate left '═'
+          <> " "
+          <> title
+          <> " "
+          <> replicate right '═'
+          <> setSGR [Reset]
+  putStrLn header
+
+-- | Run an `IO` action and print duration information after it finishes.
+withTiming
+  :: AbsoluteTime
+  -- ^ Start time for the whole @cabal-validate@ run.
+  -> String
+  -- ^ Name for describing the action.
+  --
+  -- Used in a sentence like "@title@ finished after 16.34s".
+  -> IO a
+  -- ^ Action to time.
+  -> IO a
+withTiming startTime title action = do
+  startTime' <- getAbsoluteTime
+
+  result <-
+    (Right <$> action)
+      `catch` (\exception -> pure (Left (exception :: ExitCodeException)))
+
+  endTime <- getAbsoluteTime
+
+  let duration = diffAbsoluteTime endTime startTime'
+      totalDuration = diffAbsoluteTime endTime startTime
+
+  case result of
+    Right inner -> do
+      putStrLn $
+        setSGR [Bold, BrightGreen]
+          <> title
+          <> " finished after "
+          <> formatDiffTime duration
+          <> "\nTotal time so far: "
+          <> formatDiffTime totalDuration
+          <> setSGR [Reset]
+
+      pure inner
+    Left _procFailed -> do
+      putStrLn $
+        setSGR [Bold, BrightRed]
+          <> title
+          <> " failed after "
+          <> formatDiffTime duration
+          <> "\nTotal time so far: "
+          <> formatDiffTime totalDuration
+          <> setSGR [Reset]
+
+      -- TODO: `--keep-going` mode.
+      exitFailure
diff --git a/cabal-validate/src/ProcessUtil.hs b/cabal-validate/src/ProcessUtil.hs
new file mode 100644
index 00000000000..3e27f5517a1
--- /dev/null
+++ b/cabal-validate/src/ProcessUtil.hs
@@ -0,0 +1,137 @@
+-- | Utilities for running processes and timing them.
+module ProcessUtil
+  ( timed
+  , timedWithCwd
+  ) where
+
+import Control.Exception (throwIO)
+import Control.Monad (unless)
+import Data.ByteString.Lazy (ByteString)
+import qualified Data.ByteString.Lazy as ByteString
+import Data.Text (Text)
+import qualified Data.Text as T
+import qualified Data.Text.IO as T
+import qualified Data.Text.Lazy as T (toStrict)
+import qualified Data.Text.Lazy.Encoding as T (decodeUtf8)
+import System.Directory (withCurrentDirectory)
+import System.Exit (ExitCode (ExitFailure, ExitSuccess))
+import System.Process.Typed (ExitCodeException (..), proc, readProcess, runProcess)
+
+import ANSI (SGR (BrightBlue, BrightGreen, BrightRed, Reset), setSGR)
+import Cli (Opts (..))
+import ClockUtil (diffAbsoluteTime, formatDiffTime, getAbsoluteTime)
+
+-- | Like `timed`, but runs the command in a given directory.
+timedWithCwd
+  :: Opts
+  -- ^ @cabal-validate@ options.
+  -> FilePath
+  -- ^ Path to run the command in.
+  -> FilePath
+  -- ^ The command to run.
+  -> [String]
+  -- ^ Arguments to pass to the command.
+  -> IO ()
+timedWithCwd opts cdPath command args =
+  withCurrentDirectory cdPath (timed opts command args)
+
+-- | Run a command, displaying timing information after it finishes.
+--
+-- This prints out the command to be executed before it's run, handles hiding
+-- or showing output (according to the value of `verbose`), and throws an
+-- `ExitCodeException` if the command fails.
+timed
+  :: Opts
+  -- ^ @cabal-validate@ options.
+  -> FilePath
+  -- ^ The command to run.
+  -> [String]
+  -- ^ Arguments to pass to the command.
+  -> IO ()
+timed opts command args = do
+  let prettyCommand = displayCommand command args
+      process = proc command args
+
+  startTime' <- getAbsoluteTime
+
+  -- TODO: Replace `$HOME` or `opts.cwd` for brevity?
+  putStrLn $
+    setSGR [BrightBlue]
+      <> "$ "
+      <> prettyCommand
+      <> setSGR [Reset]
+
+  (exitCode, rawStdout, rawStderr) <-
+    if verbose opts
+      then do
+        exitCode <- runProcess process
+        pure (exitCode, ByteString.empty, ByteString.empty)
+      else readProcess process
+
+  endTime <- getAbsoluteTime
+
+  let duration = diffAbsoluteTime endTime startTime'
+      totalDuration = diffAbsoluteTime endTime (startTime opts)
+
+      output = decodeStrip rawStdout <> "\n" <> decodeStrip rawStderr
+      linesLimit = 50
+      outputLines = T.lines output
+      hiddenLines = length outputLines - linesLimit
+      tailLines = drop hiddenLines outputLines
+
+  case exitCode of
+    ExitSuccess -> do
+      unless (verbose opts) $ do
+        if hiddenLines <= 0
+          then T.putStrLn output
+          else
+            T.putStrLn $
+              "("
+                <> T.pack (show hiddenLines)
+                <> " lines hidden, use `--verbose` to show)\n"
+                <> "...\n"
+                <> T.unlines tailLines
+
+      putStrLn $
+        setSGR [BrightGreen]
+          <> "Finished after "
+          <> formatDiffTime duration
+          <> ": "
+          <> prettyCommand
+          <> "\nTotal time so far: "
+          <> formatDiffTime totalDuration
+          <> setSGR [Reset]
+    ExitFailure exitCode' -> do
+      unless (verbose opts) $ do
+        T.putStrLn output
+
+      putStrLn $
+        setSGR [BrightRed]
+          <> "Failed with exit code "
+          <> show exitCode'
+          <> " after "
+          <> formatDiffTime duration
+          <> ": "
+          <> prettyCommand
+          <> "\nTotal time so far: "
+          <> formatDiffTime totalDuration
+          <> setSGR [Reset]
+
+      throwIO
+        ExitCodeException
+          { eceExitCode = exitCode
+          , eceProcessConfig = process
+          , eceStdout = rawStdout
+          , eceStderr = rawStderr
+          }
+
+-- | Decode `ByteString` output from a command and strip whitespace at the
+-- start and end.
+decodeStrip :: ByteString -> Text
+decodeStrip = T.strip . T.toStrict . T.decodeUtf8
+
+-- | Escape a shell command to display it to a user.
+--
+-- TODO: Shell escaping
+displayCommand :: String -> [String] -> String
+displayCommand command args = command <> " " <> unwords args
diff --git a/cabal-validate/src/Step.hs b/cabal-validate/src/Step.hs
new file mode 100644
index 00000000000..2636f483a79
--- /dev/null
+++ b/cabal-validate/src/Step.hs
@@ -0,0 +1,62 @@
+-- | The steps that can be run by @cabal-validate@.
+module Step
+  ( Step (..)
+  , displayStep
+  , nameToStep
+  , parseStep
+  ) where
+
+import Data.Map.Strict (Map)
+import qualified Data.Map.Strict as Map
+
+-- | A step to be run by @cabal-validate@.
+data Step
+  = PrintConfig
+  | PrintToolVersions
+  | Build
+  | Doctest
+  | LibTests
+  | LibSuite
+  | LibSuiteExtras
+  | CliTests
+  | CliSuite
+  | SolverBenchmarksTests
+  | SolverBenchmarksRun
+  | TimeSummary
+  deriving (Eq, Enum, Bounded, Show)
+
+-- | Get the display identifier for a given `Step`.
+--
+-- This is used to parse the @--step@ command-line argument.
+--
+-- Note that these names are just kebab-case variants of the `Step` constructor
+-- names; they do not attempt to describe the steps.
+displayStep :: Step -> String
+displayStep step =
+  case step of
+    PrintConfig -> "print-config"
+    PrintToolVersions -> "print-tool-versions"
+    Build -> "build"
+    Doctest -> "doctest"
+    LibTests -> "lib-tests"
+    LibSuite -> "lib-suite"
+    LibSuiteExtras -> "lib-suite-extras"
+    CliTests -> "cli-tests"
+    CliSuite -> "cli-suite"
+    SolverBenchmarksTests -> "solver-benchmarks-tests"
+    SolverBenchmarksRun -> "solver-benchmarks-run"
+    TimeSummary -> "time-summary"
+
+-- | A map from step names to `Steps`.
+--
+-- This is an inverse of `displayStep`.
+nameToStep :: Map String Step
+nameToStep =
+  Map.fromList
+    [ (displayStep step, step)
+    | step <- [minBound .. maxBound]
+    ]
+
+-- | Parse a string as a `Step`.
+parseStep :: String -> Maybe Step
+parseStep step = Map.lookup step nameToStep
diff --git a/changelog.d/i10418 b/changelog.d/i10418
new file mode 100644
index 00000000000..9a96e47a1e9
--- /dev/null
+++ b/changelog.d/i10418
@@ -0,0 +1,13 @@
+synopsis: Fix build ways for modules in executables
+packages: Cabal
+prs: #10419
+issues: #10418
+significance: significant
+
+description: {
+
+- Modules belonging to executables were being built in too many ways. For instance, if you
+had configured to build profiled library files then your executable modules would also
+be built profiled. Which was a regression in behaviour since `Cabal-3.12`.
+
+}
diff --git a/changelog.d/pr-10273 b/changelog.d/pr-10273
new file mode 100644
index 00000000000..343c871377b
--- /dev/null
+++ b/changelog.d/pr-10273
@@ -0,0 +1,19 @@
+---
+synopsis: "Show why `cabal act-as-setup configure` failed"
+packages: [Cabal]
+prs: 10273
+---
+
+When `cabal act-as-setup configure` fails, it prints a list of "missing or
+private dependencies".
+
+Now, it will show you if each failing dependency is missing, private, or an
+incompatible version:
+
+```
+Error: [Cabal-8010]
+Encountered missing or private dependencies:
+    Lib:{bar-internal,foo-internal} (missing :bar-internal),
+    base <=1.0 (installed: 4.18.2.1),
+    package-that-does-not-exist (missing)
+```
diff --git a/changelog.d/t10416 b/changelog.d/t10416
new file mode 100644
index 00000000000..071b9b1ad95
--- /dev/null
+++ b/changelog.d/t10416
@@ -0,0 +1,11 @@
+synopsis: Fix ./setup install command
+packages: Cabal
+prs: #10417
+issues: #10416
+significance: significant
+
+description: {
+
+- `./setup install` was failing with a `fromFlag NoFlag` error. It is now fixed.
+
+}
diff --git a/project-cabal/pkgs/tests.config b/project-cabal/pkgs/tests.config
index a9cec9c596f..75fe4af5ad7 100644
--- a/project-cabal/pkgs/tests.config
+++ b/project-cabal/pkgs/tests.config
@@ -2,3 +2,4 @@ packages:
     Cabal-QuickCheck
   , Cabal-tests
   , Cabal-tree-diff
+  , cabal-validate
diff --git a/validate.sh b/validate.sh
index b22e033f86e..b887b724e8f 100755
--- a/validate.sh
+++ b/validate.sh
@@ -1,554 +1,3 @@
-#!/usr/bin/env bash
-# shellcheck disable=SC2086
+#!/usr/bin/env sh
 
-# default config
-#######################################################################
-
-# We use the default ghc in PATH as default
-# Use the ghc-x.y.z trigger several errors in windows:
-# * It triggers the max path length issue:
-#   See https://github.com/haskell/cabal/issues/6271#issuecomment-1065102255
-# * It triggers a `createProcess: does not exist` error in units tests
-#   See https://github.com/haskell/cabal/issues/8049
-HC=ghc
-CABAL=cabal
-JOBS=""
-LIBTESTS=true
-CLITESTS=true
-CABALSUITETESTS=true
-LIBONLY=false
-DEPSONLY=false
-DOCTEST=false
-BENCHMARKS=false
-VERBOSE=false
-HACKAGETESTSALL=false
-
-TARGETS=""
-STEPS=""
-EXTRAHCS=""
-
-LISTSTEPS=false
-
-# Help
-#######################################################################
-
-show_usage() {
-cat <<EOF
-./validate.sh - build & test
-
-Usage: ./validate.sh [options]
-  A script which runs all the tests.
-
-Available options:
-  -j, --jobs JOBS                   cabal build -j argument (default:  $JOBS)
-      --libonly                     Test only Cabal-the-library
-      --cli                         Test both Cabal-the-library and cabal-install
-      --(no-)run-lib-tests          Run library tests
-      --(no-)run-cli-tests          Run client tests
-      --(no-)run-lib-suite          Run cabal-testsuite with library
-      --(no-)run-cli-suite          Run cabal-testsuite with client
-  -w, --with-compiler HC            With compiler
-      --with-cabal CABAL            With cabal-install
-      --extra-hc HC                 Extra compiler to run test-suite with
-      --(no-)doctest                Run doctest on library
-      --(no-)solver-benchmarks      Build and trial run solver-benchmarks
-      --complete-hackage-tests      Run hackage-tests on complete Hackage data
-      --partial-hackage-tests       Run hackage-tests on parts of Hackage data
-  -v, --verbose                     Verbose output
-  -q, --quiet                       Less output
-  -s, --step STEP                   Run only specific step (can be specified multiple times)
-      --list-steps                  List steps and build-targets and exit
-      --help                        Print this message and exit
-EOF
-}
-
-# "library"
-#######################################################################
-
-OUTPUT=$(mktemp)
-
-# `red` and `green` are used to output also the spent time in white at the end.
-# `blue` and `cyan` are used to print the spawned command, so they only have one
-# argument.
-red () {
-  printf "\033[0;31m%s\033[0m %s \n" "$1" "$2"
-}
-green () {
-  printf "\033[0;32m%s\033[0m %s \n" "$1" "$2"
-}
-blue () {
-  printf "\033[0;34m%s\033[0m\n" "$1"
-}
-cyan () {
-  printf "\033[0;96m%s\033[0m\n" "$1"
-}
-
-JOB_START_TIME=$(date +%s)
-
-timed() {
-    PRETTYCMD=$(echo "$@" | sed -E 's/\/home[^ ]*\/([^\/])/**\/\1/g')
-    blue "$PRETTYCMD"
-    start_time=$(date +%s)
-
-    if $VERBOSE; then
-        "$@" 2>&1
-    else
-        "$@" > "$OUTPUT" 2>&1
-    fi
-    # echo "MOCK" > "$OUTPUT"
-    RET=$?
-
-    end_time=$(date +%s)
-    duration=$((end_time - start_time))
-    tduration=$((end_time - JOB_START_TIME))
-
-    if [ $RET -eq 0 ]; then
-        if ! $VERBOSE; then
-            # if output is relatively short, show everything
-            if [ "$(wc -l < "$OUTPUT")" -le 50 ]; then
-                cat "$OUTPUT"
-            else
-                echo "..."
-                tail -n 20 "$OUTPUT"
-            fi
-
-            rm -f "$OUTPUT"
-        fi
-
-        green "<<< $PRETTYCMD" "($duration/$tduration sec)"
-
-        # bottom-margin
-        echo ""
-    else
-        if ! $VERBOSE; then
-            cat "$OUTPUT"
-        fi
-
-        red "<<< $PRETTYCMD" "($duration/$tduration sec, $RET)"
-        red "<<< $*" "($duration/$tduration sec, $RET)"
-        rm -f "$OUTPUT"
-        exit 1
-    fi
-}
-
-print_header() {
-    TITLE=$1
-    TITLEPAT="$(echo "$TITLE"|sed 's:.:=:g')"
-    cyan "===X========================================================================== $(date +%T) ===" \
-      | sed "s#X$TITLEPAT=# $TITLE #"
-
-}
-
-# getopt
-#######################################################################
-
-while [ $# -gt 0 ]; do
-    arg=$1
-    case $arg in
-        --help)
-            show_usage
-            exit
-            ;;
-        -j|--jobs)
-            JOBS="$2"
-            shift
-            shift
-            ;;
-        --lib-only)
-            LIBONLY=true
-            shift
-            ;;
-        --cli)
-            LIBONLY=false
-            shift
-            ;;
-        --run-lib-tests)
-            LIBTESTS=true
-            shift
-            ;;
-        --no-run-lib-tests)
-            LIBTESTS=false
-            shift
-            ;;
-        --run-cli-tests)
-            CLITESTS=true
-            shift
-            ;;
-        --no-run-cli-tests)
-            CLITESTS=false
-            shift
-            ;;
-        --run-lib-suite)
-            LIBSUITE=true
-            shift
-            ;;
-        --no-run-lib-suite)
-            LIBSUITE=false
-            shift
-            ;;
-        --run-cli-suite)
-            CLISUITE=true
-            shift
-            ;;
-        --no-run-cli-suite)
-            CLISUITE=false
-            shift
-            ;;
-        -w|--with-compiler)
-            HC=$2
-            shift
-            shift
-            ;;
-        --with-cabal)
-            CABAL=$2
-            shift
-            shift
-            ;;
-        --extra-hc)
-            EXTRAHCS="$EXTRAHCS $2"
-            shift
-            shift
-            ;;
-        --doctest)
-            DOCTEST=true
-            shift
-            ;;
-        --no-doctest)
-            DOCTEST=false
-            shift
-            ;;
-        --solver-benchmarks)
-            BENCHMARKS=true
-            shift
-            ;;
-        --no-solver-benchmarks)
-            BENCHMARKS=false
-            shift
-            ;;
-        --complete-hackage-tests)
-            HACKAGETESTSALL=true
-            shift
-            ;;
-        --partial-hackage-tests)
-            HACKAGETESTSALL=false
-            shift
-            ;;
-        -v|--verbose)
-            VERBOSE=true
-            shift
-            ;;
-        -q|--quiet)
-            VERBOSE=false
-            shift
-            ;;
-        -s|--step)
-            STEPS="$STEPS $2"
-            shift
-            shift
-            ;;
-        --list-steps)
-            LISTSTEPS=true
-            shift
-            ;;
-        *)
-            echo "Unknown option $arg"
-            exit 1
-    esac
-done
-
-# calculate steps and build targets
-#######################################################################
-
-# If there are no explicit steps given calculate them
-if $LIBONLY; then
-    CLITESTS=false
-    CLISUITE=false
-    BENCHMARKS=false
-fi
-
-if [ -z "$STEPS" ]; then
-    STEPS="print-config print-tool-versions"
-    STEPS="$STEPS build"
-    if $DOCTEST;    then STEPS="$STEPS doctest";   fi
-    if $LIBTESTS;   then STEPS="$STEPS lib-tests"; fi
-    if $LIBSUITE;   then STEPS="$STEPS lib-suite"; fi
-    if $LIBSUITE && [ -n "$EXTRAHCS" ];
-                    then STEPS="$STEPS lib-suite-extras"; fi
-    if $CLITESTS;   then STEPS="$STEPS cli-tests"; fi
-    if $CLISUITE;   then STEPS="$STEPS cli-suite"; fi
-    if $BENCHMARKS; then STEPS="$STEPS solver-benchmarks-tests solver-benchmarks-run"; fi
-    STEPS="$STEPS time-summary"
-fi
-
-TARGETS="Cabal Cabal-hooks cabal-testsuite Cabal-tests Cabal-QuickCheck Cabal-tree-diff Cabal-described"
-if ! $LIBONLY;  then TARGETS="$TARGETS cabal-install cabal-install-solver cabal-benchmarks"; fi
-if $BENCHMARKS; then TARGETS="$TARGETS solver-benchmarks"; fi
-
-if $LISTSTEPS; then
-  echo "Targets: $TARGETS"
-  echo "Steps:   $STEPS"
-  exit
-fi
-
-# Adjust runtime configuration
-#######################################################################
-
-if [ -z "$JOBS" ]; then
-    if command -v nproc >/dev/null; then
-        JOBS=$(nproc)
-    else
-        echo "Warning: \`nproc\` not found, setting \`--jobs\` to default of 4."
-        JOBS=4
-    fi
-fi
-
-TESTSUITEJOBS="-j$JOBS"
-JOBS="-j$JOBS"
-
-# assume compiler is GHC
-RUNHASKELL=$(echo "$HC" | sed -E 's/ghc(-[0-9.]*)$/runghc\1/')
-
-ARCH=$(uname -m)
-
-case "$ARCH" in
-    arm64)
-        ARCH=aarch64
-        ;;
-    x86_64)
-        ARCH=x86_64
-        ;;
-    *)
-        echo "Warning: Unknown architecture '$ARCH'"
-        ;;
-esac
-
-OS=$(uname)
-
-case "$OS" in
-    MINGW64*)
-        ARCH="$ARCH-windows"
-        ;;
-    Linux)
-        ARCH="$ARCH-linux"
-        ;;
-    Darwin)
-        ARCH="$ARCH-osx"
-        ;;
-    *)
-        echo "Warning: Unknown operating system '$OS'"
-        ARCH="$ARCH-$OS"
-        ;;
-esac
-
-if $LIBONLY; then
-    PROJECTFILE=cabal.validate-libonly.project
-else
-    PROJECTFILE=cabal.validate.project
-fi
-
-BASEHC=ghc-$($HC --numeric-version)
-BUILDDIR=dist-newstyle-validate-$BASEHC
-CABAL_TESTSUITE_BDIR="$(pwd)/$BUILDDIR/build/$ARCH/$BASEHC/cabal-testsuite-3"
-
-CABALNEWBUILD="${CABAL} build $JOBS -w $HC --builddir=$BUILDDIR --project-file=$PROJECTFILE"
-CABALLISTBIN="${CABAL} list-bin --builddir=$BUILDDIR --project-file=$PROJECTFILE"
-
-# See https://github.com/haskell/cabal/issues/9571 for why we set this for Windows
-RTSOPTS="$([ $ARCH = "x86_64-windows" ] && [ "$($HC --numeric-version)" != "9.0.2" ] && [ "$(echo -e "$(ghc --numeric-version)\n9.0.2" | sort -V | head -n1)" = "9.0.2" ] && echo "+RTS --io-manager=native" || echo "")"
-
-# header
-#######################################################################
-
-step_print_config() {
-print_header print-config
-
-cat <<EOF
-compiler:            $HC
-runhaskell:          $RUNHASKELL
-cabal-install:       $CABAL
-jobs:                $JOBS
-Cabal tests:         $LIBTESTS
-cabal-install tests: $CLITESTS
-cabal-testsuite:     $CABALSUITETESTS
-library only:        $LIBONLY
-dependencies only:   $DEPSONLY
-doctest:             $DOCTEST
-benchmarks:          $BENCHMARKS
-verbose:             $VERBOSE
-extra compilers:     $EXTRAHCS
-extra RTS options:   $RTSOPTS
-
-EOF
-}
-
-step_print_tool_versions() {
-print_header print-tool-versions
-
-timed "$HC" --version
-timed "$CABAL" --version
-
-for EXTRAHC in $EXTRAHCS; do
-    timed "$EXTRAHC" --version
-done
-}
-
-step_time_summary() {
-    print_header END
-
-    JOB_END_TIME=$(date +%s)
-    tduration=$((JOB_END_TIME - JOB_START_TIME))
-
-    cyan "!!! Validation took $tduration seconds."
-}
-
-# build
-#######################################################################
-
-step_build() {
-print_header "build"
-print_header "Step Build: dry run"
-timed $CABALNEWBUILD $TARGETS --dry-run || exit 1
-print_header "Step Build: full build plan (cached and to-be-built dependencies):"
-jq -r '."install-plan" | map(."pkg-name" + "-" + ."pkg-version" + " " + ."component-name") | join("\n")' "$BUILDDIR/cache/plan.json"
-print_header "Step Build: actual build"
-timed $CABALNEWBUILD $TARGETS || exit 1
-}
-
-# Cabal lib
-#######################################################################
-
-step_doctest() {
-print_header "Cabal: doctest"
-cabal-env --name doctest-Cabal --transitive QuickCheck
-cabal-env --name doctest-Cabal array bytestring containers deepseq directory filepath pretty process time binary unix text parsec mtl
-timed doctest -package-env=doctest-Cabal --fast Cabal/Distribution Cabal/Language
-}
-
-step_lib_tests() {
-print_header "Cabal: tests"
-
-CMD="$($CABALLISTBIN Cabal-tests:test:unit-tests) $TESTSUITEJOBS --hide-successes --with-ghc=$HC"
-(cd Cabal-tests && timed $CMD) || exit 1
-
-CMD="$($CABALLISTBIN Cabal-tests:test:check-tests) $TESTSUITEJOBS --hide-successes"
-(cd Cabal-tests && timed $CMD) || exit 1
-
-CMD="$($CABALLISTBIN Cabal-tests:test:parser-tests) $TESTSUITEJOBS --hide-successes"
-(cd Cabal-tests && timed $CMD) || exit 1
-
-CMD="$($CABALLISTBIN Cabal-tests:test:rpmvercmp) $TESTSUITEJOBS --hide-successes"
-(cd Cabal-tests && timed $CMD) || exit 1
-
-CMD="$($CABALLISTBIN Cabal-tests:test:no-thunks-test) $TESTSUITEJOBS --hide-successes"
-(cd Cabal-tests && timed $CMD) || exit 1
-
-
-# See #10284 for why this value is pinned.
-HACKAGE_TESTS_INDEX_STATE="--index-state=2024-08-25"
-
-CMD=$($CABALLISTBIN Cabal-tests:test:hackage-tests)
-(cd Cabal-tests && timed $CMD read-fields $HACKAGE_TESTS_INDEX_STATE) || exit 1
-if $HACKAGETESTSALL; then
-    (cd Cabal-tests && timed $CMD parsec $HACKAGE_TESTS_INDEX_STATE)    || exit 1
-    (cd Cabal-tests && timed $CMD roundtrip $HACKAGE_TESTS_INDEX_STATE) || exit 1
-else
-    (cd Cabal-tests && timed $CMD parsec d $HACKAGE_TESTS_INDEX_STATE)    || exit 1
-    (cd Cabal-tests && timed $CMD roundtrip k $HACKAGE_TESTS_INDEX_STATE) || exit 1
-fi
-}
-
-# Cabal cabal-testsuite
-#######################################################################
-
-step_lib_suite() {
-print_header "Cabal: cabal-testsuite"
-
-CMD="$($CABALLISTBIN cabal-testsuite:exe:cabal-tests) --builddir=$CABAL_TESTSUITE_BDIR $TESTSUITEJOBS --with-ghc=$HC --hide-successes $RTSOPTS"
-(cd cabal-testsuite && timed $CMD) || exit 1
-}
-
-step_lib_suite_extras() {
-for EXTRAHC in $EXTRAHCS; do
-
-CMD="$($CABALLISTBIN cabal-testsuite:exe:cabal-tests) --builddir=$CABAL_TESTSUITE_BDIR $TESTSUITEJOBS --with-ghc=$EXTRAHC --hide-successes"
-(cd cabal-testsuite && timed $CMD) || exit 1
-
-done
-}
-
-# cabal-install
-#######################################################################
-
-step_cli_tests() {
-print_header "cabal-install: tests"
-
-# this are sorted in asc time used, quicker tests first.
-CMD="$($CABALLISTBIN cabal-install:test:long-tests) $TESTSUITEJOBS --hide-successes"
-(cd cabal-install && timed $CMD) || exit 1
-
-# This doesn't work in parallel either
-CMD="$($CABALLISTBIN cabal-install:test:unit-tests) -j1 --hide-successes"
-(cd cabal-install && timed $CMD) || exit 1
-
-# Only single job, otherwise we fail with "Heap exhausted"
-CMD="$($CABALLISTBIN cabal-install:test:mem-use-tests) -j1 --hide-successes"
-(cd cabal-install && timed $CMD) || exit 1
-
-# This test-suite doesn't like concurrency
-CMD="$($CABALLISTBIN cabal-install:test:integration-tests2) -j1 --hide-successes --with-ghc=$HC"
-(cd cabal-install && timed $CMD) || exit 1
-}
-
-# cabal-install cabal-testsuite
-#######################################################################
-
-step_cli_suite() {
-print_header "cabal-install: cabal-testsuite"
-
-CMD="$($CABALLISTBIN cabal-testsuite:exe:cabal-tests) --builddir=$CABAL_TESTSUITE_BDIR --with-cabal=$($CABALLISTBIN cabal-install:exe:cabal) $TESTSUITEJOBS  --with-ghc=$HC --hide-successes --intree-cabal-lib=$PWD --test-tmp=$PWD/testdb $RTSOPTS"
-(cd cabal-testsuite && timed $CMD) || exit 1
-}
-
-# solver-benchmarks
-#######################################################################
-
-step_solver_benchmarks_tests() {
-print_header "solver-benchmarks: test"
-
-CMD="$($CABALLISTBIN solver-benchmarks:test:unit-tests)"
-(cd Cabal && timed $CMD) || exit 1
-}
-
-step_solver_benchmarks_run() {
-print_header "solver-benchmarks: run"
-
-SOLVEPKG=Chart-diagrams
-CMD="$($CABALLISTBIN solver-benchmarks:exe:hackage-benchmark) --cabal1=$CABAL --cabal2=$($CABALLISTBIN cabal-install:exe:cabal) --trials=5 --packages=$SOLVEPKG --print-trials"
-(cd Cabal && timed $CMD) || exit 1
-}
-
-# Steps dispatcher
-#######################################################################
-
-for step in $STEPS; do
-    case $step in
-        print-config)             step_print_config            ;;
-        print-tool-versions)      step_print_tool_versions     ;;
-        build)                    step_build                   ;;
-        doctest)                  step_doctest                 ;;
-        lib-tests)                step_lib_tests               ;;
-        cli-tests)                step_cli_tests               ;;
-        lib-suite)                step_lib_suite               ;;
-        lib-suite-extras)         step_lib_suite_extras        ;;
-        cli-suite)                step_cli_suite               ;;
-        solver-benchmarks-tests)  step_solver_benchmarks_tests ;;
-        solver-benchmarks-run)    step_solver_benchmarks_run   ;;
-        time-summary)             step_time_summary            ;;
-        *)
-            echo "Invalid step $step"
-            exit 1
-            ;;
-    esac
-done
-
-#######################################################################
+cabal run cabal-validate:exe:cabal-validate -- "$@"