Make EmptySkyValue not serializable

Should be a singleton, should never be serialized or deserialized,
but add equals and hash code as well for good measure.

--
MOS_MIGRATED_REVID=105888511

2 files changed, 68 insertions, 1 deletions

diff --git a/src/main/java/com/google/devtools/build/skyframe/EmptySkyValue.java b/src/main/java/com/google/devtools/build/skyframe/EmptySkyValue.java
index 723e83e137..3ee8bba123 100644
--- a/src/main/java/com/google/devtools/build/skyframe/EmptySkyValue.java
+++ b/src/main/java/com/google/devtools/build/skyframe/EmptySkyValue.java
@@ -13,6 +13,9 @@
 // limitations under the License.
 package com.google.devtools.build.skyframe;
 
+import java.io.ObjectInputStream;
+import java.io.ObjectOutputStream;
+
 /**
  * A SkyValue with no attached data. Preferable to a specialized empty value class to minimize
  * bloat.
@@ -21,5 +24,25 @@ public final class EmptySkyValue implements SkyValue {
   public static final EmptySkyValue INSTANCE = new EmptySkyValue();
 
   private EmptySkyValue() {}
-}
 
+  @Override
+  public int hashCode() {
+    return 422;
+  }
+
+  @Override
+  public boolean equals(Object other) {
+    return other instanceof EmptySkyValue;
+  }
+
+  // SkyValue implements Serializable, however we don't want to support Java serialization.
+  @SuppressWarnings("unused")
+  private void writeObject(ObjectOutputStream unused) {
+    throw new UnsupportedOperationException("Java serialization not supported");
+  }
+
+  @SuppressWarnings("unused")
+  private void readObject(ObjectInputStream unused) {
+    throw new UnsupportedOperationException("Java serialization not supported");
+  }
+}
diff --git a/src/test/java/com/google/devtools/build/skyframe/EmptySkyValueTest.java b/src/test/java/com/google/devtools/build/skyframe/EmptySkyValueTest.java
new file mode 100644
index 0000000000..61239175dc
--- /dev/null
+++ b/src/test/java/com/google/devtools/build/skyframe/EmptySkyValueTest.java
@@ -0,0 +1,44 @@
+// Copyright 2015 The Bazel Authors. 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.skyframe;
+
+import static com.google.common.truth.Truth.assertThat;
+import static org.junit.Assert.fail;
+
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.io.ObjectOutputStream;
+
+/** Tests for {@link EmptySkyValue}. */
+@RunWith(JUnit4.class)
+public class EmptySkyValueTest {
+
+  @Test
+  public void testNotSerializable() throws IOException {
+    ObjectOutputStream objOut = new ObjectOutputStream(new ByteArrayOutputStream());
+
+    try {
+      objOut.writeObject(EmptySkyValue.INSTANCE);
+      fail("Expected exception");
+    } catch (UnsupportedOperationException e) {
+      assertThat(e).hasMessage("Java serialization not supported");
+    }
+  }
+
+}
+