Add support for loading multiple components into one repl session

There are several parts to this patch which are logically distinct but
work together to support the overal goal of starting a GHCi session with
multiple packages loaded at once.

1. When a user writes "cabal repl <target>" then if the user is using a
   compiler > ghc-9.4.* then we will attempt to start a multi-session
   which loads the selected targets into one multi-package session of
   GHC.
1a. The closure property states that in order to load components `p` and `q` into
    the same session that if `p` depends on `z` and `z` depends on `q`
    then `z` must also be loaded into the session.
1b. Only inplace packages are able to be loaded into a multi session (if a component
    `z` exists then it is already made into an inplace package by
    cabal). Therefore cabal has already engineered that there is source
    code locally available for all packages which we will want to load
    into a session.

2. The solver is unmodified, the solver is given the repl targets and
   creates a build plan as before. After the solver is completed then in
   `setRootTargets` and `pruneInstallPlan` we modify the install plan to
   enforce the closure property and mark which dependencies need to be
   promised.

   * Mark the current components as `BuildInPlaceOnly InMemory`, which
     indicates to the compiler that it is to be built in a GHC
     multi-session.
   * Augment the component repl targets to indicate that components
     required by the closure property (in addition to normal targets)
     will be loaded into the repl.
   * Modify the dependency edges in `compLibDependencies` to indicate
     which dependencies are the promised ones (which is precisely
     components which are `BuildInPlaceOnly InMemory` build styles).
     This is the field which is eventually used to populate the
     `--dependency` argument to `./Setup configure`.

Fixes #8491

Cabal-tests/tests/UnitTests/Distribution/Utils/Structured.hs

@@ -29,7 +29,7 @@ tests = testGroup "Distribution.Utils.Structured"
     , testCase "GenericPackageDescription" $
       md5Check (Proxy :: Proxy GenericPackageDescription) 0xa3e9433662ecf0c7a3c26f6d75a53ba1
     , testCase "LocalBuildInfo" $
-      md5Check (Proxy :: Proxy LocalBuildInfo) 0x91ffcd61bbd83525e8edba877435a031
+      md5Check (Proxy :: Proxy LocalBuildInfo) 0x30ebb8fffa1af2aefa9432ff4028eef8
 #endif
     ]
 

Cabal/src/Distribution/Types/AnnotatedId.hs

@@ -1,3 +1,4 @@
+{-# LANGUAGE DeriveFunctor #-}
 module Distribution.Types.AnnotatedId (
     AnnotatedId(..)
 ) where
@@ -19,7 +20,7 @@ data AnnotatedId id = AnnotatedId {
         ann_cname :: ComponentName,
         ann_id    :: id
     }
-    deriving (Show)
+    deriving (Show, Functor)
 
 instance Eq id => Eq (AnnotatedId id) where
     x == y = ann_id x == ann_id y
@@ -29,6 +30,3 @@ instance Ord id => Ord (AnnotatedId id) where
 
 instance Package (AnnotatedId id) where
     packageId = ann_pid
-
-instance Functor AnnotatedId where
-    fmap f (AnnotatedId pid cn x) = AnnotatedId pid cn (f x)

cabal-install-solver/src/Distribution/Solver/Types/ComponentDeps.hs

@@ -24,6 +24,7 @@ module Distribution.Solver.Types.ComponentDeps (
   , insert
   , zip
   , filterDeps
+  , mapDeps
   , fromLibraryDeps
   , fromSetupDeps
   , fromInstalled
@@ -149,6 +150,10 @@ zip (ComponentDeps d1) (ComponentDeps d2) =
 filterDeps :: (Component -> a -> Bool) -> ComponentDeps a -> ComponentDeps a
 filterDeps p = ComponentDeps . Map.filterWithKey p . unComponentDeps
 
+-- | Keep only selected components (and their associated deps info).
+mapDeps :: (Component -> a -> b) -> ComponentDeps a -> ComponentDeps b
+mapDeps p = ComponentDeps . Map.mapWithKey p . unComponentDeps
+
 -- | ComponentDeps containing library dependencies only
 fromLibraryDeps :: a -> ComponentDeps a
 fromLibraryDeps = singleton ComponentLib

cabal-install-solver/src/Distribution/Solver/Types/ConstraintSource.hs

@@ -36,6 +36,10 @@ data ConstraintSource =
   -- target, when a more specific source is not known.
   | ConstraintSourceConfigFlagOrTarget
 
+  -- | Constraint introduced by --enable-multi-repl, which requires features
+  -- from Cabal >= 3.11
+  | ConstraintSourceMultiRepl
+
   -- | The source of the constraint is not specified.
   | ConstraintSourceUnknown
 
@@ -65,6 +69,8 @@ showConstraintSource ConstraintSourceNonUpgradeablePackage =
 showConstraintSource ConstraintSourceFreeze = "cabal freeze"
 showConstraintSource ConstraintSourceConfigFlagOrTarget =
     "config file, command line flag, or user target"
+showConstraintSource ConstraintSourceMultiRepl =
+    "--enable-multi-repl"
 showConstraintSource ConstraintSourceUnknown = "unknown source"
 showConstraintSource ConstraintSetupCabalMinVersion =
     "minimum version of Cabal used by Setup.hs"

cabal-install/cabal-install.cabal

@@ -159,6 +159,7 @@ library
         Distribution.Client.ProjectPlanning.Types
         Distribution.Client.RebuildMonad
         Distribution.Client.Reconfigure
+        Distribution.Client.ReplFlags
         Distribution.Client.Run
         Distribution.Client.Sandbox
         Distribution.Client.Sandbox.PackageEnvironment

cabal-install/src/Distribution/Client/CmdListBin.hs

@@ -187,12 +187,12 @@ listbinAction flags@NixStyleFlags{..} args globalFlags = do
         -- here and in PlanOutput,
         -- use binDirectoryFor?
         bin_file' s =
-            if elabBuildStyle elab == BuildInplaceOnly
+            if isInplaceBuildStyle (elabBuildStyle elab)
             then dist_dir </> "build" </> prettyShow s </> prettyShow s <.> exeExtension plat
             else InstallDirs.bindir (elabInstallDirs elab) </> prettyShow s <.> exeExtension plat
 
         flib_file' s =
-            if elabBuildStyle elab == BuildInplaceOnly
+            if isInplaceBuildStyle (elabBuildStyle elab)
             then dist_dir </> "build" </> prettyShow s </> ("lib" ++ prettyShow s) <.> dllExtension plat
             else InstallDirs.bindir (elabInstallDirs elab) </> ("lib" ++ prettyShow s) <.> dllExtension plat