1 files changed, 57 insertions, 0 deletions
diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/FileSymlinkCycleUniquenessValue.java b/src/main/java/com/google/devtools/build/lib/skyframe/FileSymlinkCycleUniquenessValue.java
new file mode 100644
index 0000000000..627276d357
--- /dev/null
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/FileSymlinkCycleUniquenessValue.java
@@ -0,0 +1,57 @@
+// 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.base.Preconditions;
+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 cycle is reported exactly once. This is achieved by
+ * forcing the same value key for two logically equivalent cycles (e.g. ['a' -> 'b' -> 'c' -> 'a']
+ * and ['b' -> 'c' -> 'a' -> 'b'], and letting Skyframe do its magic. 
+ */
+class FileSymlinkCycleUniquenessValue implements SkyValue {
+
+  public static final FileSymlinkCycleUniquenessValue INSTANCE =
+      new FileSymlinkCycleUniquenessValue();
+
+  private FileSymlinkCycleUniquenessValue() {
+  }
+
+  static SkyKey key(ImmutableList<RootedPath> cycle) {
+    Preconditions.checkState(!cycle.isEmpty()); 
+    return new SkyKey(SkyFunctions.FILE_SYMLINK_CYCLE_UNIQUENESS, canonicalize(cycle));
+  }
+
+  private static ImmutableList<RootedPath> canonicalize(ImmutableList<RootedPath> cycle) {
+    int minPos = 0;
+    String minString = cycle.get(0).toString();
+    for (int i = 1; i < cycle.size(); i++) {
+      String candidateString = cycle.get(i).toString();
+      if (candidateString.compareTo(minString) < 0) {
+        minPos = i;
+        minString = candidateString;
+      }
+    }
+    ImmutableList.Builder<RootedPath> builder = ImmutableList.builder();
+    for (int i = 0; i < cycle.size(); i++) {
+      int pos = (minPos + i) % cycle.size();
+      builder.add(cycle.get(pos));
+    }
+    return builder.build();
+  }
+}