builtins.path: Propagate references from derivation outputs

src/libexpr/primops.cc

@@ -2807,11 +2807,18 @@ static void addPath(
     const NixStringContext & context)
 {
     try {
-        if (path.accessor == state.rootFS && state.store->isInStore(path.path.abs())) {
+        StorePathSet refs;
+
+        if (path.accessor == state.rootFS && state.store->isInStore(path.path.abs()) && !context.empty()) {
             // FIXME: handle CA derivation outputs (where path needs to
             // be rewritten to the actual output).
             auto rewrites = state.realiseContext(context);
             path = {path.accessor, CanonPath(rewriteStrings(path.path.abs(), rewrites))};
+            auto [storePath, subPath] = state.store->toStorePath(path.path.abs());
+            try {
+                refs = state.store->queryPathInfo(storePath)->references;
+            } catch (Error &) { // FIXME: should be InvalidPathError
+            }
         }
 
         std::unique_ptr<PathFilter> filter;
@@ -2824,18 +2831,27 @@ static void addPath(
         std::optional<StorePath> expectedStorePath;
         if (expectedHash)
             expectedStorePath = state.store->makeFixedOutputPathFromCA(
-                name, ContentAddressWithReferences::fromParts(method, *expectedHash, {}));
+                name, ContentAddressWithReferences::fromParts(method, *expectedHash, {refs}));
 
         if (!expectedHash || !state.store->isValidPath(*expectedStorePath)) {
-            auto dstPath = fetchToStore(
-                state.fetchSettings,
-                *state.store,
-                path.resolveSymlinks(),
-                settings.readOnlyMode ? FetchMode::DryRun : FetchMode::Copy,
-                name,
-                method,
-                filter.get(),
-                state.repair);
+            // FIXME: support refs in fetchToStore()?
+            auto dstPath = refs.empty() ? fetchToStore(
+                                              state.fetchSettings,
+                                              *state.store,
+                                              path.resolveSymlinks(),
+                                              settings.readOnlyMode ? FetchMode::DryRun : FetchMode::Copy,
+                                              name,
+                                              method,
+                                              filter.get(),
+                                              state.repair)
+                                        : state.store->addToStore(
+                                              name,
+                                              path.resolveSymlinks(),
+                                              method,
+                                              HashAlgorithm::SHA256,
+                                              refs,
+                                              filter ? *filter.get() : defaultPathFilter,
+                                              state.repair);
             if (expectedHash && expectedStorePath != dstPath)
                 state.error<EvalError>("store path mismatch in (possibly filtered) path added from '%s'", path)
                     .atPos(pos)

tests/functional/import-from-derivation.nix

@@ -46,4 +46,24 @@ rec {
   };
 
   importAddPathExpr = import addPathExpr;
+
+  symlink = mkDerivation {
+    name = "symlink";
+    buildCommand = ''
+      mkdir $out
+      echo hello world > $out/text
+      ln -s $out/text $out/symlink
+      ln -s ${step1} $out/symlink2
+    '';
+  };
+
+  pathFromDerivation = builtins.path {
+    name = "path-from-derivation";
+    path = "${symlink}/";
+  };
+
+  pathFromDerivation2 = builtins.path {
+    name = "path-from-derivation";
+    path = "${symlink}/text";
+  };
 }

tests/functional/import-from-derivation.sh

@@ -29,6 +29,15 @@ fi
 outPath2=$(nix-build ./import-from-derivation.nix -A addPath --no-out-link)
 [[ "$(cat "$outPath2")" = BLAFOO579 ]]
 
+# Test that applying builtins.path to the result of a derivation propagates all references
+for attr in pathFromDerivation pathFromDerivation2; do
+    outPath3=$(nix eval --raw -f ./import-from-derivation.nix "$attr")
+    refs=$(nix path-info --json "$outPath3" | jq -r '.[].references.[]')
+    [[ $(printf "%s" "$refs" | wc -w) = 2 ]]
+    [[ $refs =~ -step1 ]]
+    [[ $refs =~ -symlink ]]
+done
+
 # Test that IFD works with a chroot store.
 if canUseSandbox; then