Introduce libnixflake

Makefile

@@ -18,6 +18,7 @@ makefiles = \
   src/libfetchers/local.mk \
   src/libmain/local.mk \
   src/libexpr/local.mk \
+  src/libflake/local.mk \
   src/libcmd/local.mk \
   src/nix/local.mk \
   src/libutil-c/local.mk \
@@ -45,7 +46,8 @@ makefiles += \
   tests/unit/libstore-support/local.mk \
   tests/unit/libfetchers/local.mk \
   tests/unit/libexpr/local.mk \
-  tests/unit/libexpr-support/local.mk
+  tests/unit/libexpr-support/local.mk \
+  tests/unit/libflake/local.mk
 endif
 
 ifeq ($(ENABLE_FUNCTIONAL_TESTS), yes)

maintainers/flake-module.nix

@@ -65,14 +65,6 @@
             ''^src/libexpr/eval-settings\.hh$''
             ''^src/libexpr/eval\.cc$''
             ''^src/libexpr/eval\.hh$''
-            ''^src/libexpr/flake/config\.cc$''
-            ''^src/libexpr/flake/flake\.cc$''
-            ''^src/libexpr/flake/flake\.hh$''
-            ''^src/libexpr/flake/flakeref\.cc$''
-            ''^src/libexpr/flake/flakeref\.hh$''
-            ''^src/libexpr/flake/lockfile\.cc$''
-            ''^src/libexpr/flake/lockfile\.hh$''
-            ''^src/libexpr/flake/url-name\.cc$''
             ''^src/libexpr/function-trace\.cc$''
             ''^src/libexpr/gc-small-vector\.hh$''
             ''^src/libexpr/get-drvs\.cc$''
@@ -127,6 +119,14 @@
             ''^src/libfetchers/tarball\.hh$''
             ''^src/libfetchers/git\.cc$''
             ''^src/libfetchers/mercurial\.cc$''
+            ''^src/libflake/flake/config\.cc$''
+            ''^src/libflake/flake/flake\.cc$''
+            ''^src/libflake/flake/flake\.hh$''
+            ''^src/libflake/flake/flakeref\.cc$''
+            ''^src/libflake/flake/flakeref\.hh$''
+            ''^src/libflake/flake/lockfile\.cc$''
+            ''^src/libflake/flake/lockfile\.hh$''
+            ''^src/libflake/flake/url-name\.cc$''
             ''^src/libmain/common-args\.cc$''
             ''^src/libmain/common-args\.hh$''
             ''^src/libmain/loggers\.cc$''
@@ -436,8 +436,6 @@
             ''^tests/unit/libexpr/derived-path\.cc''
             ''^tests/unit/libexpr/error_traces\.cc''
             ''^tests/unit/libexpr/eval\.cc''
-            ''^tests/unit/libexpr/flake/flakeref\.cc''
-            ''^tests/unit/libexpr/flake/url-name\.cc''
             ''^tests/unit/libexpr/json\.cc''
             ''^tests/unit/libexpr/main\.cc''
             ''^tests/unit/libexpr/primops\.cc''
@@ -446,6 +444,8 @@
             ''^tests/unit/libexpr/value/context\.cc''
             ''^tests/unit/libexpr/value/print\.cc''
             ''^tests/unit/libfetchers/public-key\.cc''
+            ''^tests/unit/libflake/flakeref\.cc''
+            ''^tests/unit/libflake/url-name\.cc''
             ''^tests/unit/libstore-support/tests/derived-path\.cc''
             ''^tests/unit/libstore-support/tests/derived-path\.hh''
             ''^tests/unit/libstore-support/tests/nix_api_store\.hh''

src/libcmd/common-eval-args.cc

@@ -15,7 +15,20 @@
 namespace nix {
 
 EvalSettings evalSettings {
-    settings.readOnlyMode
+    settings.readOnlyMode,
+    {
+        {
+            "flake",
+            [](ref<Store> store, std::string_view rest) {
+                experimentalFeatureSettings.require(Xp::Flakes);
+                // FIXME `parseFlakeRef` should take a `std::string_view`.
+                auto flakeRef = parseFlakeRef(std::string { rest }, {}, true, false);
+                debug("fetching flake search path element '%s''", rest);
+                auto storePath = flakeRef.resolve(store).fetchTree(store).first;
+                return store->toRealPath(storePath);
+            },
+        },
+    },
 };
 
 static GlobalConfig::Register rEvalSettings(&evalSettings);

src/libcmd/local.mk

@@ -6,10 +6,10 @@ libcmd_DIR := $(d)
 
 libcmd_SOURCES := $(wildcard $(d)/*.cc)
 
-libcmd_CXXFLAGS += $(INCLUDE_libutil) $(INCLUDE_libstore) $(INCLUDE_libfetchers) $(INCLUDE_libexpr) $(INCLUDE_libmain)
+libcmd_CXXFLAGS += $(INCLUDE_libutil) $(INCLUDE_libstore) $(INCLUDE_libfetchers) $(INCLUDE_libexpr) $(INCLUDE_libflake) $(INCLUDE_libmain)
 
 libcmd_LDFLAGS = $(EDITLINE_LIBS) $(LOWDOWN_LIBS) $(THREAD_LDFLAGS)
 
-libcmd_LIBS = libstore libutil libexpr libmain libfetchers
+libcmd_LIBS = libutil libstore libfetchers libflake libexpr libmain
 
 $(eval $(call install-file-in, $(buildprefix)$(d)/nix-cmd.pc, $(libdir)/pkgconfig, 0644))

src/libexpr/eval-settings.cc

@@ -45,8 +45,9 @@ static Strings parseNixPath(const std::string & s)
     return res;
 }
 
-EvalSettings::EvalSettings(bool & readOnlyMode)
+EvalSettings::EvalSettings(bool & readOnlyMode, EvalSettings::LookupPathHooks lookupPathHooks)
     : readOnlyMode{readOnlyMode}
+    , lookupPathHooks{lookupPathHooks}
 {
     auto var = getEnv("NIX_PATH");
     if (var) nixPath = parseNixPath(*var);

src/libexpr/eval-settings.hh

@@ -5,9 +5,40 @@
 
 namespace nix {
 
+class Store;
+
 struct EvalSettings : Config
 {
-    EvalSettings(bool & readOnlyMode);
+    /**
+     * Function used to interpet look path entries of a given scheme.
+     *
+     * The argument is the non-scheme part of the lookup path entry (see
+     * `LookupPathHooks` below).
+     *
+     * The return value is (a) whether the entry was valid, and, if so,
+     * what does it map to.
+     *
+     * @todo Return (`std::optional` of) `SourceAccssor` or something
+     * more structured instead of mere `std::string`?
+     */
+    using LookupPathHook = std::optional<std::string>(ref<Store> store, std::string_view);
+
+    /**
+     * Map from "scheme" to a `LookupPathHook`.
+     *
+     * Given a lookup path value (i.e. either the whole thing, or after
+     * the `<key>=`) in the form of:
+     *
+     * ```
+     * <scheme>:<arbitrary string>
+     * ```
+     *
+     * if `<scheme>` is a key in this map, then `<arbitrary string>` is
+     * passed to the hook that is the value in this map.
+     */
+    using LookupPathHooks = std::map<std::string, std::function<LookupPathHook>>;
+
+    EvalSettings(bool & readOnlyMode, LookupPathHooks lookupPathHooks = {});
 
     bool & readOnlyMode;
 
@@ -17,6 +48,8 @@ struct EvalSettings : Config
 
     static std::string resolvePseudoUrl(std::string_view url);
 
+    LookupPathHooks lookupPathHooks;
+
     Setting<bool> enableNativeCode{this, false, "allow-unsafe-native-code-during-evaluation", R"(
         Enable built-in functions that allow executing native code.
 

src/libexpr/eval.cc

@@ -21,7 +21,6 @@
 #include "url.hh"
 #include "fetch-to-store.hh"
 #include "tarball.hh"
-#include "flake/flakeref.hh"
 #include "parser-tab.hh"
 
 #include <algorithm>
@@ -2760,30 +2759,36 @@ std::optional<std::string> EvalState::resolveLookupPathPath(const LookupPath::Pa
     auto i = lookupPathResolved.find(value);
     if (i != lookupPathResolved.end()) return i->second;
 
-    std::optional<std::string> res;
+    auto finish = [&](std::string res) {
+        debug("resolved search path element '%s' to '%s'", value, res);
+        lookupPathResolved.emplace(value, res);
+        return res;
+    };
 
     if (EvalSettings::isPseudoUrl(value)) {
         try {
             auto accessor = fetchers::downloadTarball(
                 EvalSettings::resolvePseudoUrl(value)).accessor;
             auto storePath = fetchToStore(*store, SourcePath(accessor), FetchMode::Copy);
-            res = { store->toRealPath(storePath) };
+            return finish(store->toRealPath(storePath));
         } catch (Error & e) {
             logWarning({
                 .msg = HintFmt("Nix search path entry '%1%' cannot be downloaded, ignoring", value)
             });
         }
     }
 
-    else if (hasPrefix(value, "flake:")) {
-        experimentalFeatureSettings.require(Xp::Flakes);
-        auto flakeRef = parseFlakeRef(value.substr(6), {}, true, false);
-        debug("fetching flake search path element '%s''", value);
-        auto storePath = flakeRef.resolve(store).fetchTree(store).first;
-        res = { store->toRealPath(storePath) };
+    if (auto colPos = value.find(':'); colPos != value.npos) {
+        auto scheme = value.substr(0, colPos);
+        auto rest = value.substr(colPos + 1);
+        if (auto * hook = get(settings.lookupPathHooks, scheme)) {
+            auto res = (*hook)(store, rest);
+            if (res)
+                return finish(std::move(*res));
+        }
     }
 
-    else {
+    {
         auto path = absPath(value);
 
         /* Allow access to paths in the search path. */
@@ -2800,22 +2805,17 @@ std::optional<std::string> EvalState::resolveLookupPathPath(const LookupPath::Pa
         }
 
         if (pathExists(path))
-            res = { path };
+            return finish(std::move(path));
         else {
             logWarning({
                 .msg = HintFmt("Nix search path entry '%1%' does not exist, ignoring", value)
             });
-            res = std::nullopt;
         }
     }
 
-    if (res)
-        debug("resolved search path element '%s' to '%s'", value, *res);
-    else
-        debug("failed to resolve search path element '%s'", value);
+    debug("failed to resolve search path element '%s'", value);
+    return std::nullopt;
 
-    lookupPathResolved.emplace(value, res);
-    return res;
 }
 
 

src/libexpr/local.mk

@@ -8,7 +8,6 @@ libexpr_SOURCES := \
   $(wildcard $(d)/*.cc) \
   $(wildcard $(d)/value/*.cc) \
   $(wildcard $(d)/primops/*.cc) \
-  $(wildcard $(d)/flake/*.cc) \
   $(d)/lexer-tab.cc \
   $(d)/parser-tab.cc
 # Not just for this library itself, but also for downstream libraries using this library
@@ -45,8 +44,6 @@ $(eval $(call install-file-in, $(buildprefix)$(d)/nix-expr.pc, $(libdir)/pkgconf
 
 $(foreach i, $(wildcard src/libexpr/value/*.hh), \
   $(eval $(call install-file-in, $(i), $(includedir)/nix/value, 0644)))
-$(foreach i, $(wildcard src/libexpr/flake/*.hh), \
-  $(eval $(call install-file-in, $(i), $(includedir)/nix/flake, 0644)))
 
 $(d)/primops.cc: $(d)/imported-drv-to-derivation.nix.gen.hh
 

src/libfetchers/fetch-settings.hh

@@ -70,30 +70,6 @@ struct FetchSettings : public Config
     Setting<bool> warnDirty{this, true, "warn-dirty",
         "Whether to warn about dirty Git/Mercurial trees."};
 
-    Setting<std::string> flakeRegistry{this, "https://channels.nixos.org/flake-registry.json", "flake-registry",
-        R"(
-          Path or URI of the global flake registry.
-
-          When empty, disables the global flake registry.
-        )",
-        {}, true, Xp::Flakes};
-
-    Setting<bool> useRegistries{this, true, "use-registries",
-        "Whether to use flake registries to resolve flake references.",
-        {}, true, Xp::Flakes};
-
-    Setting<bool> acceptFlakeConfig{this, false, "accept-flake-config",
-        "Whether to accept nix configuration from a flake without prompting.",
-        {}, true, Xp::Flakes};
-
-    Setting<std::string> commitLockFileSummary{
-        this, "", "commit-lock-file-summary",
-        R"(
-          The commit summary to use when committing changed flake lock files. If
-          empty, the summary is generated based on the action performed.
-        )",
-        {"commit-lockfile-summary"}, true, Xp::Flakes};
-
     Setting<bool> trustTarballsFromGitForges{
         this, true, "trust-tarballs-from-git-forges",
         R"(
@@ -108,7 +84,6 @@ struct FetchSettings : public Config
           `narHash` attribute is specified,
           e.g. `github:NixOS/patchelf/7c2f768bf9601268a4e71c2ebe91e2011918a70f?narHash=sha256-PPXqKY2hJng4DBVE0I4xshv/vGLUskL7jl53roB8UdU%3D`.
         )"};
-
 };
 
 // FIXME: don't use a global variable.

src/libfetchers/registry.cc

@@ -1,12 +1,11 @@
 #include "registry.hh"
 #include "tarball.hh"
 #include "users.hh"
+#include "config-global.hh"
 #include "globals.hh"
 #include "store-api.hh"
 #include "local-fs-store.hh"
 
-#include "fetch-settings.hh"
-
 #include <nlohmann/json.hpp>
 
 namespace nix::fetchers {
@@ -149,10 +148,25 @@ void overrideRegistry(
     flagRegistry->add(from, to, extraAttrs);
 }
 
+struct RegistrySettings : Config
+{
+    Setting<std::string> flakeRegistry{this, "https://channels.nixos.org/flake-registry.json", "flake-registry",
+        R"(
+          Path or URI of the global flake registry.
+
+          When empty, disables the global flake registry.
+        )",
+        {}, true, Xp::Flakes};
+};
+
+RegistrySettings registrySettings;
+
+static GlobalConfig::Register rRegistrySettings(&registrySettings);
+
 static std::shared_ptr<Registry> getGlobalRegistry(ref<Store> store)
 {
     static auto reg = [&]() {
-        auto path = fetchSettings.flakeRegistry.get();
+        auto path = registrySettings.flakeRegistry.get();
         if (path == "") {
             return std::make_shared<Registry>(Registry::Global); // empty registry
         }

src/libflake/flake-settings.cc

@@ -0,0 +1,12 @@
+#include "flake-settings.hh"
+#include "config-global.hh"
+
+namespace nix {
+
+FlakeSettings::FlakeSettings() {}
+
+FlakeSettings flakeSettings;
+
+static GlobalConfig::Register rFlakeSettings(&flakeSettings);
+
+}