Elegantly handle unbounded file symlink resolutions, e.g. 'a' -> 'b' -> 'a/nope'.

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MOS_MIGRATED_REVID=99337668

1 files changed, 39 insertions, 0 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/FileSymlinkInfiniteExpansionUniquenessValue.java b/src/main/java/com/google/devtools/build/lib/skyframe/FileSymlinkInfiniteExpansionUniquenessValue.java
new file mode 100644
index 0000000000..e866b51572
--- /dev/null
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/FileSymlinkInfiniteExpansionUniquenessValue.java
@@ -0,0 +1,39 @@
+// Copyright 2015 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.ImmutableList;
+import com.google.devtools.build.lib.vfs.RootedPath;
+import com.google.devtools.build.skyframe.SkyKey;
+import com.google.devtools.build.skyframe.SkyValue;
+
+/**
+ * A value for ensuring that a file symlink expansion error is reported exactly once. This is
+ * achieved by forcing the same value key for two logically equivalent expansion errors (e.g.
+ * ['a' -> 'b' -> 'c' -> 'a/nope'] and ['b' -> 'c' -> 'a' -> 'a/nope']), and letting Skyframe do
+ * its magic.
+ */
+class FileSymlinkInfiniteExpansionUniquenessValue implements SkyValue {
+  static final FileSymlinkInfiniteExpansionUniquenessValue INSTANCE =
+      new FileSymlinkInfiniteExpansionUniquenessValue();
+
+  private FileSymlinkInfiniteExpansionUniquenessValue() {
+  }
+
+  static SkyKey key(ImmutableList<RootedPath> cycle) {
+    return AbstractFileSymlinkExceptionUniquenessValue.key(
+        SkyFunctions.FILE_SYMLINK_INFINITE_EXPANSION_UNIQUENESS, cycle);
+  }
+}
+