1 files changed, 45 insertions, 0 deletions
diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/FileSymlinkCycleUniquenessFunction.java b/src/main/java/com/google/devtools/build/lib/skyframe/FileSymlinkCycleUniquenessFunction.java
new file mode 100644
index 0000000000..a0604b5b42
--- /dev/null
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/FileSymlinkCycleUniquenessFunction.java
@@ -0,0 +1,45 @@
+// 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.ImmutableList;
+import com.google.devtools.build.lib.events.Event;
+import com.google.devtools.build.lib.vfs.RootedPath;
+import com.google.devtools.build.skyframe.SkyFunction;
+import com.google.devtools.build.skyframe.SkyKey;
+import com.google.devtools.build.skyframe.SkyValue;
+
+/** A value builder that has the side effect of reporting a file symlink cycle. */
+public class FileSymlinkCycleUniquenessFunction implements SkyFunction {
+
+  @SuppressWarnings("unchecked")  // Cast from Object to ImmutableList<RootedPath>.
+  @Override
+  public SkyValue compute(SkyKey skyKey, Environment env) {
+    StringBuilder cycleMessage = new StringBuilder("circular symlinks detected\n");
+    cycleMessage.append("[start of symlink cycle]\n");
+    for (RootedPath rootedPath : (ImmutableList<RootedPath>) skyKey.argument()) {
+      cycleMessage.append(rootedPath.asPath() + "\n");
+    }
+    cycleMessage.append("[end of symlink cycle]");
+    // The purpose of this value builder is the side effect of emitting an error message exactly
+    // once per build per unique cycle.
+    env.getListener().handle(Event.error(cycleMessage.toString()));
+    return FileSymlinkCycleUniquenessValue.INSTANCE;
+  }
+
+  @Override
+  public String extractTag(SkyKey skyKey) {
+    return null;
+  }
+}