Ignore local registries for lock file generation

When resolving indirect flake references like `nixpkgs` in `flake.nix`
files, Nix will no longer use the system and user flake registries. It
will only use the global flake registry and overrides given on the
command line via `--override-flake`.

src/libflake/flake/flake.cc

@@ -54,7 +54,13 @@ static std::tuple<StorePath, FlakeRef, FlakeRef> fetchOrSubstituteTree(
             fetched.emplace(originalRef.fetchTree(state.store));
         } else {
             if (allowLookup) {
-                resolvedRef = originalRef.resolve(state.store);
+                resolvedRef = originalRef.resolve(
+                    state.store,
+                    [](fetchers::Registry::RegistryType type) {
+                        /* Only use the global registry and CLI flags
+                           to resolve indirect flakerefs. */
+                        return type == fetchers::Registry::Flag || type == fetchers::Registry::Global;
+                    });
                 auto fetchedResolved = lookupInFlakeCache(flakeCache, originalRef);
                 if (!fetchedResolved) fetchedResolved.emplace(resolvedRef.fetchTree(state.store));
                 flakeCache.push_back({resolvedRef, *fetchedResolved});

src/libflake/flake/flakeref.cc

@@ -3,7 +3,6 @@
 #include "url.hh"
 #include "url-parts.hh"
 #include "fetchers.hh"
-#include "registry.hh"
 
 namespace nix {
 
@@ -36,7 +35,9 @@ std::ostream & operator << (std::ostream & str, const FlakeRef & flakeRef)
     return str;
 }
 
-FlakeRef FlakeRef::resolve(ref<Store> store) const
+FlakeRef FlakeRef::resolve(
+    ref<Store> store,
+    const fetchers::RegistryFilter & filter) const
 {
     auto [input2, extraAttrs] = lookupInRegistries(store, input);
     return FlakeRef(std::move(input2), fetchers::maybeGetStrAttr(extraAttrs, "dir").value_or(subdir));

src/libflake/flake/flakeref.hh

@@ -6,6 +6,7 @@
 #include "types.hh"
 #include "fetchers.hh"
 #include "outputs-spec.hh"
+#include "registry.hh"
 
 namespace nix {
 
@@ -57,7 +58,9 @@ struct FlakeRef
 
     fetchers::Attrs toAttrs() const;
 
-    FlakeRef resolve(ref<Store> store) const;
+    FlakeRef resolve(
+        ref<Store> store,
+        const fetchers::RegistryFilter & filter = {}) const;
 
     static FlakeRef fromAttrs(
         const fetchers::Settings & fetchSettings,