Update from Google.
--
MOE_MIGRATED_REVID=85702957
diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/ExternalFilesHelper.java b/src/main/java/com/google/devtools/build/lib/skyframe/ExternalFilesHelper.java
new file mode 100644
index 0000000..ce858de
--- /dev/null
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/ExternalFilesHelper.java
@@ -0,0 +1,97 @@
+// Copyright 2014 Google Inc. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+package com.google.devtools.build.lib.skyframe;
+
+import com.google.common.collect.ImmutableSet;
+import com.google.devtools.build.lib.pkgcache.PathPackageLocator;
+import com.google.devtools.build.lib.vfs.Path;
+import com.google.devtools.build.lib.vfs.RootedPath;
+import com.google.devtools.build.skyframe.SkyFunction;
+
+import java.util.Set;
+import java.util.concurrent.atomic.AtomicReference;
+
+/** Common utilities for dealing with files outside the package roots. */
+class ExternalFilesHelper {
+
+ private final AtomicReference<PathPackageLocator> pkgLocator;
+ private final Set<Path> immutableDirs;
+
+ ExternalFilesHelper(AtomicReference<PathPackageLocator> pkgLocator) {
+ this(pkgLocator, ImmutableSet.<Path>of());
+ }
+
+ ExternalFilesHelper(AtomicReference<PathPackageLocator> pkgLocator, Set<Path> immutableDirs) {
+ this.pkgLocator = pkgLocator;
+ this.immutableDirs = immutableDirs;
+ }
+
+ private enum FileType {
+ // A file inside the package roots.
+ INTERNAL_FILE,
+
+ // A file outside the package roots that we may pretends is immutable.
+ EXTERNAL_IMMUTABLE_FILE,
+
+ // A file outside the package roots about which we may make no other assumptions.
+ EXTERNAL_MUTABLE_FILE,
+ }
+
+ private FileType getFileType(RootedPath rootedPath) {
+ // TODO(bazel-team): This is inefficient when there are a lot of package roots or there are a
+ // lot of immutable directories. Consider either explicitly preventing this case or using a more
+ // efficient approach here (e.g. use a trie for determing if a file is under an immutable
+ // directory).
+ if (!pkgLocator.get().getPathEntries().contains(rootedPath.getRoot())) {
+ Path path = rootedPath.asPath();
+ for (Path immutableDir : immutableDirs) {
+ if (path.startsWith(immutableDir)) {
+ return FileType.EXTERNAL_IMMUTABLE_FILE;
+ }
+ }
+ return FileType.EXTERNAL_MUTABLE_FILE;
+ }
+ return FileType.INTERNAL_FILE;
+ }
+
+ public boolean shouldAssumeImmutable(RootedPath rootedPath) {
+ return getFileType(rootedPath) == FileType.EXTERNAL_IMMUTABLE_FILE;
+ }
+
+ public void maybeAddDepOnBuildId(RootedPath rootedPath, SkyFunction.Environment env) {
+ if (getFileType(rootedPath) == FileType.EXTERNAL_MUTABLE_FILE) {
+ // For files outside the package roots that are not assumed to be immutable, add a dependency
+ // on the build_id. This is sufficient for correctness; all other files will be handled by
+ // diff awareness of their respective package path, but these files need to be addressed
+ // separately.
+ //
+ // Using the build_id here seems to introduce a performance concern because the upward
+ // transitive closure of these external files will get eagerly invalidated on each
+ // incremental build (e.g. if every file had a transitive dependency on the filesystem root,
+ // then we'd have a big performance problem). But this a non-issue by design:
+ // - We don't add a dependency on the parent directory at the package root boundary, so the
+ // only transitive dependencies from files inside the package roots to external files are
+ // through symlinks. So the upwards transitive closure of external files is small.
+ // - The only way external source files get into the skyframe graph in the first place is
+ // through symlinks outside the package roots, which we neither want to encourage nor
+ // optimize for since it is not common. So the set of external files is small.
+ //
+ // The above reasoning doesn't hold for bazel, because external repositories
+ // (e.g. new_local_repository) cause lots of external symlinks to be present in the build.
+ // So bazel pretends that these external repositories are immutable to avoid the performance
+ // penalty described above.
+ PrecomputedValue.dependOnBuildId(env);
+ }
+ }
+}
