Refuse to rebuild changes with no patch sets

The implementation of NoteDb requires every commit in the meta graph
to have a patch set ID. The implementation of ChangeRebuildImpl was
unintentionally setting the patch set to the current patch set of the
change, even if there were no actual PatchSet entities in ReviewDb to
back that up. Also unintentionally, parsing this result back would
succeed, and even produce the correct Change fields to make
ChangeBundle's diff happy.

Changes in this state are really corrupt, though, and can't be shown
in the UI, among other things. We should just ignore them when
converting to NoteDb, which is equivalent to obliterating them.

Change-Id: I376d89770fb3b3870e7111e5170882a14419e0a2

gerrit-acceptance-tests/src/test/java/com/google/gerrit/acceptance/server/notedb/ChangeRebuilderIT.java

@@ -59,6 +59,7 @@ import com.google.gerrit.server.git.RepoRefCache;
 import com.google.gerrit.server.git.UpdateException;
 import com.google.gerrit.server.notedb.ChangeBundle;
 import com.google.gerrit.server.notedb.ChangeNotes;
+import com.google.gerrit.server.notedb.ChangeRebuilder.NoPatchSetsException;
 import com.google.gerrit.server.notedb.NoteDbChangeState;
 import com.google.gerrit.server.notedb.NoteDbUpdateManager;
 import com.google.gerrit.server.notedb.TestChangeRebuilderWrapper;
@@ -954,6 +955,22 @@ public class ChangeRebuilderIT extends AbstractDaemonTest {
     assertChangeUpToDate(false, id);
   }
 
+  @Test
+  public void rebuildChangeWithNoPatchSets() throws Exception {
+    PushOneCommit.Result r = createChange();
+    Change.Id id = r.getPatchSetId().getParentKey();
+    db.changes().beginTransaction(id);
+    try {
+      db.patchSets().delete(db.patchSets().byChange(id));
+      db.commit();
+    } finally {
+      db.rollback();
+    }
+
+    exception.expect(NoPatchSetsException.class);
+    checker.rebuildAndCheckChanges(id);
+  }
+
   private void assertChangesReadOnly(RestApiException e) throws Exception {
     Throwable cause = e.getCause();
     assertThat(cause).isInstanceOf(UpdateException.class);

gerrit-server/src/main/java/com/google/gerrit/server/notedb/ChangeRebuilder.java

@@ -32,6 +32,15 @@ import java.io.IOException;
 import java.util.concurrent.Callable;
 
 public abstract class ChangeRebuilder {
+  public static class NoPatchSetsException extends OrmException {
+    private static final long serialVersionUID = 1L;
+
+    NoPatchSetsException(Change.Id changeId) {
+      super("Change " + changeId
+          + " cannot be rebuilt because it has no patch sets");
+    }
+  }
+
   private final SchemaFactory<ReviewDb> schemaFactory;
 
   protected ChangeRebuilder(SchemaFactory<ReviewDb> schemaFactory) {

gerrit-server/src/main/java/com/google/gerrit/server/notedb/ChangeRebuilderImpl.java

@@ -287,6 +287,8 @@ public class ChangeRebuilderImpl extends ChangeRebuilder {
       for (Change.Id changeId : allChanges.get(project)) {
         try {
           buildUpdates(manager, ChangeBundle.fromReviewDb(db, changeId));
+        } catch (NoPatchSetsException e) {
+          log.warn(e.getMessage());
         } catch (Throwable t) {
           log.error("Failed to rebuild change " + changeId, t);
           ok = false;
@@ -304,6 +306,10 @@ public class ChangeRebuilderImpl extends ChangeRebuilder {
       throws IOException, OrmException {
     manager.setCheckExpectedState(false);
     Change change = new Change(bundle.getChange());
+    if (bundle.getPatchSets().isEmpty()) {
+      throw new NoPatchSetsException(change.getId());
+    }
+
     PatchSet.Id currPsId = change.currentPatchSetId();
     // We will rebuild all events, except for draft comments, in buckets based
     // on author and timestamp.