Move some code to a new libnixflake

For now, this sits between `libnixfetchers` and `libnixflakes`, but
eventually I hope it can sit atop `libexprs`. Baby steps though, this is
fine for now.

The immediate impact of this is that some flakes-specific parts of
`libnixfetchers` can move here, after which I hearby declare libfetchers
is free of layer violations, and we are thus (baring something unrelated
I missed) ready to stabilize `builtins.fetchTree`.

Makefile

@@ -4,6 +4,7 @@ makefiles = \
   src/libutil/local.mk \
   src/libstore/local.mk \
   src/libfetchers/local.mk \
+  src/libflake/local.mk \
   src/libmain/local.mk \
   src/libexpr/local.mk \
   src/libcmd/local.mk \

src/libcmd/local.mk

@@ -6,10 +6,10 @@ libcmd_DIR := $(d)
 
 libcmd_SOURCES := $(wildcard $(d)/*.cc)
 
-libcmd_CXXFLAGS += -I src/libutil -I src/libstore -I src/libexpr -I src/libmain -I src/libfetchers
+libcmd_CXXFLAGS += -I src/libutil -I src/libstore -I src/libfetchers -I src/libflake -I src/libexpr -I src/libmain
 
 libcmd_LDFLAGS = $(EDITLINE_LIBS) $(LOWDOWN_LIBS) -pthread
 
-libcmd_LIBS = libstore libutil libexpr libmain libfetchers
+libcmd_LIBS = libutil libstore libfetchers libflake libexpr libmain
 
 $(eval $(call install-file-in, $(d)/nix-cmd.pc, $(libdir)/pkgconfig, 0644))

src/libexpr/flake/config.cc

@@ -1,6 +1,6 @@
 #include "flake.hh"
 #include "globals.hh"
-#include "fetch-settings.hh"
+#include "flake-settings.hh"
 
 #include <nlohmann/json.hpp>
 
@@ -50,7 +50,7 @@ void ConfigFile::apply()
         else
             assert(false);
 
-        if (!whitelist.count(baseName) && !nix::fetchSettings.acceptFlakeConfig) {
+        if (!whitelist.count(baseName) && !nix::flakeSettings.acceptFlakeConfig) {
             bool trusted = false;
             auto trustedList = readTrustedList();
             auto tlname = get(trustedList, name);

src/libexpr/flake/flake.cc

@@ -8,6 +8,7 @@
 #include "fetchers.hh"
 #include "finally.hh"
 #include "fetch-settings.hh"
+#include "flake-settings.hh"
 
 namespace nix {
 
@@ -329,7 +330,7 @@ LockedFlake lockFlake(
 
     FlakeCache flakeCache;
 
-    auto useRegistries = lockFlags.useRegistries.value_or(fetchSettings.useRegistries);
+    auto useRegistries = lockFlags.useRegistries.value_or(flakeSettings.useRegistries);
 
     auto flake = getFlake(state, topRef, useRegistries, flakeCache);
 
@@ -664,7 +665,7 @@ LockedFlake lockFlake(
                             }
                             std::string cm;
 
-                            cm = fetchSettings.commitLockFileSummary.get();
+                            cm = flakeSettings.commitLockFileSummary.get();
 
                             if (cm == "") {
                                 cm = fmt("%s: %s", relPath, lockFileExists ? "Update" : "Add");
@@ -761,7 +762,7 @@ static void prim_getFlake(EvalState & state, const PosIdx pos, Value * * args, V
             LockFlags {
                 .updateLockFile = false,
                 .writeLockFile = false,
-                .useRegistries = !evalSettings.pureEval && fetchSettings.useRegistries,
+                .useRegistries = !evalSettings.pureEval && flakeSettings.useRegistries,
                 .allowUnlocked = !evalSettings.pureEval,
             }),
         v);

src/libexpr/local.mk

@@ -12,9 +12,9 @@ libexpr_SOURCES := \
   $(d)/lexer-tab.cc \
   $(d)/parser-tab.cc
 
-libexpr_CXXFLAGS += -I src/libutil -I src/libstore -I src/libfetchers -I src/libmain -I src/libexpr
+libexpr_CXXFLAGS += -I src/libutil -I src/libstore -I src/libfetchers -I src/libflake  -I src/libexpr
 
-libexpr_LIBS = libutil libstore libfetchers
+libexpr_LIBS = libutil libstore libfetchers libflake
 
 libexpr_LDFLAGS += -lboost_context -pthread
 ifdef HOST_LINUX

src/libfetchers/fetch-settings.hh

@@ -70,31 +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-lockfile-summary",
-        R"(
-          The commit summary to use when committing changed flake lock files. If
-          empty, the summary is generated based on the action performed.
-        )",
-        {}, true, Xp::Flakes};
 };
 
 // FIXME: don't use a global variable.

src/libflake/flake-settings.cc

@@ -0,0 +1,13 @@
+#include "flake-settings.hh"
+
+namespace nix {
+
+FlakeSettings::FlakeSettings()
+{
+}
+
+FlakeSettings flakeSettings;
+
+static GlobalConfig::Register rFlakeSettings(&flakeSettings);
+
+}

src/libflake/flake-settings.hh

@@ -0,0 +1,48 @@
+#pragma once
+///@file
+
+#include "types.hh"
+#include "config.hh"
+#include "util.hh"
+
+#include <map>
+#include <limits>
+
+#include <sys/types.h>
+
+namespace nix {
+
+struct FlakeSettings : public Config
+{
+    FlakeSettings();
+
+    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-lockfile-summary",
+        R"(
+          The commit summary to use when committing changed flake lock files. If
+          empty, the summary is generated based on the action performed.
+        )",
+        {}, true, Xp::Flakes};
+};
+
+// FIXME: don't use a global variable.
+extern FlakeSettings flakeSettings;
+
+}

src/libflake/local.mk

@@ -0,0 +1,13 @@
+libraries += libflake
+
+libflake_NAME = libnixflake
+
+libflake_DIR := $(d)
+
+libflake_SOURCES := $(wildcard $(d)/*.cc)
+
+libflake_CXXFLAGS += -I src/libutil -I src/libstore -I src/libfetchers
+
+libflake_LDFLAGS += -pthread
+
+libflake_LIBS = libutil libstore libfetchers

src/libfetchers/registry.cc → src/libflake/registry.cc

@@ -5,7 +5,7 @@
 #include "store-api.hh"
 #include "local-fs-store.hh"
 
-#include "fetch-settings.hh"
+#include "flake-settings.hh"
 
 #include <nlohmann/json.hpp>
 
@@ -152,7 +152,7 @@ void overrideRegistry(
 static std::shared_ptr<Registry> getGlobalRegistry(ref<Store> store)
 {
     static auto reg = [&]() {
-        auto path = fetchSettings.flakeRegistry.get();
+        auto path = flakeSettings.flakeRegistry.get();
         if (path == "") {
             return std::make_shared<Registry>(Registry::Global); // empty registry
         }

src/nix/local.mk

@@ -14,9 +14,9 @@ nix_SOURCES := \
   $(wildcard src/nix-instantiate/*.cc) \
   $(wildcard src/nix-store/*.cc) \
 
-nix_CXXFLAGS += -I src/libutil -I src/libstore -I src/libfetchers -I src/libexpr -I src/libmain -I src/libcmd -I doc/manual
+nix_CXXFLAGS += -I src/libutil -I src/libstore -I src/libfetchers -I src/libflake -I src/libexpr -I src/libmain -I src/libcmd -I doc/manual
 
-nix_LIBS = libexpr libmain libfetchers libstore libutil libcmd
+nix_LIBS = libexpr libmain libflake libfetchers libstore libutil libcmd
 
 nix_LDFLAGS = -pthread $(SODIUM_LIBS) $(EDITLINE_LIBS) $(BOOST_LDFLAGS) $(LOWDOWN_LIBS)