Make the path fetcher lazy

Note: the path fetcher no longer computes lastModified, because that's
not lazy.

Author: edolstra

src/libfetchers/fetch-to-store.cc

@@ -58,7 +58,7 @@ std::pair<StorePath, Hash> fetchToStore2(
         }
     } else {
         static auto barf = getEnv("_NIX_TEST_BARF_ON_UNCACHEABLE").value_or("") == "1";
-        if (barf && !filter)
+        if (barf && !filter && !(path.to_string().starts_with("/") || path.to_string().starts_with("«path:/")))
             throw Error("source path '%s' is uncacheable (filter=%d)", path, (bool) filter);
         // FIXME: could still provide in-memory caching keyed on `SourcePath`.
         debug("source path '%s' is uncacheable", path);

src/libfetchers/path.cc

@@ -146,36 +146,23 @@ struct PathInputScheme : InputScheme
         auto absPath = getAbsPath(input);
 
         // FIXME: check whether access to 'path' is allowed.
+
+        auto accessor = makeFSSourceAccessor(absPath);
+
         auto storePath = store.maybeParseStorePath(absPath.string());
 
-        if (storePath)
+        if (storePath) {
             store.addTempRoot(*storePath);
 
-        time_t mtime = 0;
-        if (!storePath || storePath->name() != "source" || !store.isValidPath(*storePath)) {
-            Activity act(*logger, lvlTalkative, actUnknown, fmt("copying %s to the store", absPath));
-            // FIXME: try to substitute storePath.
-            auto src = sinkToSource(
-                [&](Sink & sink) { mtime = dumpPathAndGetMtime(absPath.string(), sink, defaultPathFilter); });
-            storePath = store.addToStoreFromDump(*src, "source");
+            // To prevent `fetchToStore()` copying the path again to Nix
+            // store, pre-create an entry in the fetcher cache.
+            auto info = store.queryPathInfo(*storePath);
+            accessor->fingerprint = fmt("path:%s", info->narHash.to_string(HashFormat::SRI, true));
+            settings.getCache()->upsert(
+                makeSourcePathToHashCacheKey(*accessor->fingerprint, ContentAddressMethod::Raw::NixArchive, "/"),
+                {{"hash", info->narHash.to_string(HashFormat::SRI, true)}});
         }
 
-        auto accessor = store.requireStoreObjectAccessor(*storePath);
-
-        // To prevent `fetchToStore()` copying the path again to Nix
-        // store, pre-create an entry in the fetcher cache.
-        auto info = store.queryPathInfo(*storePath);
-        accessor->fingerprint =
-            fmt("path:%s", store.queryPathInfo(*storePath)->narHash.to_string(HashFormat::SRI, true));
-        settings.getCache()->upsert(
-            makeSourcePathToHashCacheKey(*accessor->fingerprint, ContentAddressMethod::Raw::NixArchive, "/"),
-            {{"hash", info->narHash.to_string(HashFormat::SRI, true)}});
-
-        /* Trust the lastModified value supplied by the user, if
-           any. It's not a "secure" attribute so we don't care. */
-        if (!input.getLastModified())
-            input.attrs.insert_or_assign("lastModified", uint64_t(mtime));
-
         return {accessor, std::move(input)};
     }
 };

tests/functional/fetchPath.sh

@@ -3,9 +3,9 @@
 source common.sh
 
 touch "$TEST_ROOT/foo" -t 202211111111
-# We only check whether 2022-11-1* **:**:** is the last modified date since
-# `lastModified` is transformed into UTC in `builtins.fetchTarball`.
-[[ "$(nix eval --impure --raw --expr "(builtins.fetchTree \"path://$TEST_ROOT/foo\").lastModifiedDate")" =~ 2022111.* ]]
+
+# The path fetcher does not return lastModified.
+[[ "$(nix eval --impure --expr "(builtins.fetchTree \"path://$TEST_ROOT/foo\") ? lastModifiedDate")" = false ]]
 
 # Check that we can override lastModified for "path:" inputs.
 [[ "$(nix eval --impure --expr "(builtins.fetchTree { type = \"path\"; path = \"$TEST_ROOT/foo\"; lastModified = 123; }).lastModified")" = 123 ]]

tests/functional/flakes/flakes.sh

@@ -381,7 +381,6 @@ nix build -o "$TEST_ROOT"/result git+file://"$flakeGitBare"
 mkdir -p "$flake5Dir"
 writeDependentFlake "$flake5Dir"
 nix flake lock path://"$flake5Dir"
-[[ "$(nix flake metadata "path://$flake5Dir" --json | jq -r .fingerprint)" != null ]]
 
 # Test tarball flakes.
 tar cfz "$TEST_ROOT"/flake.tar.gz -C "$TEST_ROOT" flake5

tests/functional/nix-profile.sh

@@ -4,6 +4,8 @@ source common.sh
 
 TODO_NixOS
 
+requireGit
+
 clearStore
 clearProfiles
 
@@ -12,7 +14,7 @@ restartDaemon
 
 # Make a flake.
 flake1Dir=$TEST_ROOT/flake1
-mkdir -p "$flake1Dir"
+createGitRepo "$flake1Dir"
 
 # shellcheck disable=SC2154,SC1039
 cat > "$flake1Dir"/flake.nix <<EOF
@@ -50,6 +52,9 @@ printf false > "$flake1Dir"/ca.nix
 
 cp "${config_nix}" "$flake1Dir"/
 
+git -C "$flake1Dir" add flake.nix config.nix who version ca.nix
+git -C "$flake1Dir" commit -m 'Initial'
+
 # Test upgrading from nix-env.
 nix-env -f ./user-envs.nix -i foo-1.0
 nix profile list | grep -A2 'Name:.*foo' | grep 'Store paths:.*foo-1.0'
@@ -224,11 +229,11 @@ error: An existing package already provides the following file:
        The conflicting packages have a priority of 5.
        To prioritise the new package:
 
-         nix profile add path:${flake2Dir}#packages.${system}.default --priority 4
+         nix profile add git+file://${flake2Dir}#packages.${system}.default --priority 4
 
        To prioritise the existing package:
 
-         nix profile add path:${flake2Dir}#packages.${system}.default --priority 6
+         nix profile add git+file://${flake2Dir}#packages.${system}.default --priority 6
 EOF
 )
 [[ $("$TEST_HOME"/.nix-profile/bin/hello) = "Hello World" ]]