Allow removing approvals from a label in the notedb

This allows the server to indicate a previously-saved approval is for
a label that no longer exists or the user no longer has permissions to
vote on.

Reuse the "Label" footer, with "-Label-Name" indicating a tombstone.

Change-Id: I8c390a28c639d1642aa434eb8c816d6c89f0ebdd

gerrit-server/src/test/java/com/google/gerrit/server/notedb/ChangeNotesTest.java

@@ -21,6 +21,7 @@ import static java.util.concurrent.TimeUnit.MILLISECONDS;
 import static java.util.concurrent.TimeUnit.SECONDS;
 import static org.easymock.EasyMock.expect;
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
 
 import com.google.common.collect.ImmutableSetMultimap;
 import com.google.common.collect.Iterables;
@@ -55,7 +56,9 @@ import com.google.gerrit.server.util.TimeUtil;
 import com.google.gerrit.testutil.FakeAccountCache;
 import com.google.gerrit.testutil.FakeRealm;
 import com.google.gerrit.testutil.InMemoryRepositoryManager;
+import com.google.gwtorm.client.KeyUtil;
 import com.google.gwtorm.server.OrmException;
+import com.google.gwtorm.server.StandardKeyEncoder;
 import com.google.inject.Guice;
 import com.google.inject.Injector;
 import com.google.inject.util.Providers;
@@ -98,6 +101,7 @@ public class ChangeNotesTest {
   @Before
   public void setUp() throws Exception {
     setTimeForTesting();
+    KeyUtil.setEncoderImpl(new StandardKeyEncoder());
 
     serverIdent = new PersonIdent(
         "Gerrit Server", "noreply@gerrit.com", TimeUtil.nowTs(), TZ);
@@ -206,6 +210,27 @@ public class ChangeNotesTest {
     }
   }
 
+  @Test
+  public void approvalTombstoneCommitFormat() throws Exception {
+    Change c = newChange();
+    ChangeUpdate update = newUpdate(c, changeOwner);
+    update.removeApproval("Code-Review");
+    update.commit();
+
+    RevWalk walk = new RevWalk(repo);
+    try {
+      RevCommit commit = walk.parseCommit(update.getRevision());
+      walk.parseBody(commit);
+      assertEquals("Update patch set 1\n"
+          + "\n"
+          + "Patch-set: 1\n"
+          + "Label: -Code-Review\n",
+          commit.getFullMessage());
+    } finally {
+      walk.release();
+    }
+  }
+
   @Test
   public void approvalsOnePatchSet() throws Exception {
     Change c = newChange();
@@ -320,6 +345,28 @@ public class ChangeNotesTest {
     assertEquals(truncate(after(c, 2000)), psas.get(1).getGranted());
   }
 
+  @Test
+  public void approvalsTombstone() throws Exception {
+    Change c = newChange();
+    ChangeUpdate update = newUpdate(c, changeOwner);
+    update.putApproval("Not-For-Long", (short) 1);
+    update.commit();
+
+    ChangeNotes notes = newNotes(c);
+    PatchSetApproval psa = Iterables.getOnlyElement(
+        notes.getApprovals().get(c.currentPatchSetId()));
+    assertEquals(1, psa.getAccountId().get());
+    assertEquals("Not-For-Long", psa.getLabel());
+    assertEquals((short) 1, psa.getValue());
+
+    update = newUpdate(c, changeOwner);
+    update.removeApproval("Not-For-Long");
+    update.commit();
+
+    notes = newNotes(c);
+    assertTrue(notes.getApprovals().isEmpty());
+  }
+
   @Test
   public void multipleReviewers() throws Exception {
     Change c = newChange();