Include merge result commit in change-merged stream-event

When CI gets a change merged event what the CI most likely wants
to build is not the last patch set of the change but the result
on the target branch.

If the merge of a change was not fast forward these are two
separate commits.

With this change the CI can retrieve the merge result from the
newRev of a change merged event.

Change-Id: I1d61ab253f4028a26cfbf0427b33873c294ee29e

Documentation/cmd-stream-events.txt

@@ -72,6 +72,8 @@ patchSet:: link:json.html#patchSet[patchSet attribute]
 
 submitter:: link:json.html#account[account attribute]
 
+newRev:: The resulting revision of the merge.
+
 eventCreatedOn:: Time in seconds since the UNIX epoch when this event was
 created.
 

gerrit-acceptance-tests/src/test/java/com/google/gerrit/acceptance/rest/change/AbstractSubmit.java

@@ -22,11 +22,14 @@ import static com.google.gerrit.extensions.common.ListChangesOption.CURRENT_REVI
 import static com.google.gerrit.extensions.common.ListChangesOption.DETAILED_LABELS;
 
 import com.google.common.collect.Lists;
+import com.google.common.collect.Maps;
 import com.google.gerrit.acceptance.AbstractDaemonTest;
 import com.google.gerrit.acceptance.GitUtil;
 import com.google.gerrit.acceptance.PushOneCommit;
 import com.google.gerrit.acceptance.RestResponse;
 import com.google.gerrit.acceptance.SshSession;
+import com.google.gerrit.common.ChangeHooks;
+import com.google.gerrit.common.ChangeListener;
 import com.google.gerrit.extensions.api.changes.ReviewInput;
 import com.google.gerrit.extensions.api.changes.SubmitInput;
 import com.google.gerrit.extensions.common.ChangeInfo;
@@ -41,7 +44,12 @@ import com.google.gerrit.reviewdb.client.PatchSet;
 import com.google.gerrit.reviewdb.client.PatchSetApproval;
 import com.google.gerrit.reviewdb.client.Project;
 import com.google.gerrit.server.ApprovalsUtil;
+import com.google.gerrit.server.CurrentUser;
+import com.google.gerrit.server.IdentifiedUser;
+import com.google.gerrit.server.events.ChangeEvent;
+import com.google.gerrit.server.events.ChangeMergedEvent;
 import com.google.gerrit.server.notedb.ChangeNotes;
+import com.google.gerrit.server.project.ListBranches.BranchInfo;
 import com.google.gerrit.server.project.PutConfig;
 import com.google.gson.reflect.TypeToken;
 import com.google.gwtorm.server.OrmException;
@@ -66,16 +74,39 @@ import java.io.IOException;
 import java.sql.Timestamp;
 import java.util.Collections;
 import java.util.List;
+import java.util.Map;
 
 public abstract class AbstractSubmit extends AbstractDaemonTest {
+
+  private Map<String, String> mergeResults;
+
   @Inject
   private ChangeNotes.Factory notesFactory;
 
   @Inject
   private ApprovalsUtil approvalsUtil;
 
+  @Inject
+  private IdentifiedUser.GenericFactory factory;
+
+  @Inject
+  ChangeHooks hooks;
+
   @Before
   public void setUp() throws Exception {
+    mergeResults = Maps.newHashMap();
+    CurrentUser listenerUser = factory.create(user.id);
+    hooks.addChangeListener(new ChangeListener() {
+
+      @Override
+      public void onChangeEvent(ChangeEvent event) {
+        if (event instanceof ChangeMergedEvent) {
+          ChangeMergedEvent cMEvent = (ChangeMergedEvent) event;
+          mergeResults.put(cMEvent.change.number, cMEvent.newRev);
+        }
+      }
+
+    }, listenerUser);
     project = new Project.NameKey("p2");
   }
 
@@ -181,10 +212,28 @@ public abstract class AbstractSubmit extends AbstractDaemonTest {
           newGson().fromJson(r.getReader(),
               new TypeToken<ChangeInfo>() {}.getType());
       assertThat(change.status).isEqualTo(ChangeStatus.MERGED);
+
+      checkMergeResult(change);
     }
     r.consume();
   }
 
+  private void checkMergeResult(ChangeInfo change) throws IOException {
+    // Get the revision of the branch after the submit to compare with the
+    // newRev of the ChangeMergedEvent.
+    RestResponse b =
+        adminSession.get("/projects/" + project.get() + "/branches/"
+            + change.branch);
+    if (b.getStatusCode() == HttpStatus.SC_OK) {
+      BranchInfo branch =
+          newGson().fromJson(b.getReader(),
+              new TypeToken<BranchInfo>() {}.getType());
+      assertThat(branch.revision).isEqualTo(
+          mergeResults.get(Integer.toString(change._number)));
+    }
+    b.consume();
+  }
+
   private void approve(String changeId) throws IOException {
     RestResponse r = adminSession.post(
         "/changes/" + changeId + "/revisions/current/review",

gerrit-server/src/main/java/com/google/gerrit/common/ChangeHookRunner.java

@@ -446,14 +446,16 @@ public class ChangeHookRunner implements ChangeHooks, LifecycleListener {
     }
 
     @Override
-    public void doChangeMergedHook(final Change change, final Account account,
+  public void doChangeMergedHook(final Change change, final Account account,
-          final PatchSet patchSet, final ReviewDb db) throws OrmException {
+      final PatchSet patchSet, final ReviewDb db, String mergeResultRev)
+      throws OrmException {
         final ChangeMergedEvent event = new ChangeMergedEvent();
         final AccountState owner = accountCache.get(change.getOwner());
 
         event.change = eventFactory.asChangeAttribute(change);
         event.submitter = eventFactory.asAccountAttribute(account);
         event.patchSet = eventFactory.asPatchSetAttribute(patchSet);
+        event.newRev = mergeResultRev;
         fireEvent(change, event, db);
 
         final List<String> args = new ArrayList<>();
@@ -465,6 +467,7 @@ public class ChangeHookRunner implements ChangeHooks, LifecycleListener {
         addArg(args, "--topic", event.change.topic);
         addArg(args, "--submitter", getDisplayName(account));
         addArg(args, "--commit", event.patchSet.revision);
+        addArg(args, "--newrev", mergeResultRev);
 
         runHook(change.getProject(), changeMergedHook, args);
     }

gerrit-server/src/main/java/com/google/gerrit/common/ChangeHooks.java

@@ -79,10 +79,11 @@ public interface ChangeHooks {
    * @param change The change itself.
    * @param account The gerrit user who submitted the change.
    * @param patchSet The patchset that was merged.
+   * @param mergeResultRev The SHA-1 of the merge result revision.
    * @throws OrmException
    */
   public void doChangeMergedHook(Change change, Account account,
-      PatchSet patchSet, ReviewDb db) throws OrmException;
+      PatchSet patchSet, ReviewDb db, String mergeResultRev) throws OrmException;
 
   /**
    * Fire the Merge Failed Hook.

gerrit-server/src/main/java/com/google/gerrit/common/DisabledChangeHooks.java

@@ -44,7 +44,7 @@ public final class DisabledChangeHooks implements ChangeHooks {
 
   @Override
   public void doChangeMergedHook(Change change, Account account,
-      PatchSet patchSet, ReviewDb db) {
+      PatchSet patchSet, ReviewDb db, String mergeResultRev) {
   }
 
   @Override

gerrit-server/src/main/java/com/google/gerrit/server/events/ChangeMergedEvent.java

@@ -27,6 +27,7 @@ public class ChangeMergedEvent extends ChangeEvent {
   public ChangeAttribute change;
   public PatchSetAttribute patchSet;
   public AccountAttribute submitter;
+  public String newRev;
 
   @Override
   public String getType() {

gerrit-server/src/main/java/com/google/gerrit/server/git/MergeOp.java

@@ -171,7 +171,7 @@ public class MergeOp {
   private RevWalk rw;
   private RevFlag canMergeFlag;
   private CodeReviewCommit branchTip;
-  private CodeReviewCommit mergeTip;
+  private MergeTip mergeTip;
   private ObjectInserter inserter;
   private PersonIdent refLogIdent;
 
@@ -277,11 +277,11 @@ public class MergeOp {
             branchUpdate = openBranch();
           }
           SubmitStrategy strategy = createStrategy(submitType);
-          preMerge(strategy, toMerge.get(submitType));
+          MergeTip mergeTip = preMerge(strategy, toMerge.get(submitType));
           RefUpdate update = updateBranch(strategy, branchUpdate);
           reopen = true;
 
-          updateChangeStatus(toSubmit.get(submitType));
+          updateChangeStatus(toSubmit.get(submitType), mergeTip);
           updateSubscriptions(toSubmit.get(submitType));
           if (update != null) {
             fireRefUpdated(update);
@@ -315,7 +315,7 @@ public class MergeOp {
         logDebug("Adding {} changes to merge on next run", toMerge.size());
       }
 
-      updateChangeStatus(toUpdate);
+      updateChangeStatus(toUpdate, mergeTip);
 
       for (CodeReviewCommit commit : potentiallyStillSubmittableOnNextRun) {
         Capable capable = isSubmitStillPossible(commit);
@@ -403,7 +403,7 @@ public class MergeOp {
     return true;
   }
 
-  private void preMerge(SubmitStrategy strategy,
+  private MergeTip preMerge(SubmitStrategy strategy,
       List<CodeReviewCommit> toMerge) throws MergeException {
     logDebug("Running submit strategy {} for {} commits",
         strategy.getClass().getSimpleName(), toMerge.size());
@@ -411,6 +411,7 @@ public class MergeOp {
     refLogIdent = strategy.getRefLogIdent();
     logDebug("Produced {} new commits", strategy.getNewCommits().size());
     commits.putAll(strategy.getNewCommits());
+    return mergeTip;
   }
 
   private SubmitStrategy createStrategy(SubmitType submitType)
@@ -604,7 +605,7 @@ public class MergeOp {
                 idstr, ps.getId());
             commit.setStatusCode(CommitMergeStatus.ALREADY_MERGED);
             try {
-              setMerged(chg, null);
+              setMerged(chg, null, commit.getName());
             } catch (OrmException e) {
               logError("Cannot mark change " + chg.getId() + " merged", e);
             }
@@ -650,11 +651,13 @@ public class MergeOp {
 
   private RefUpdate updateBranch(SubmitStrategy strategy,
       RefUpdate branchUpdate) throws MergeException {
-    if (branchTip == mergeTip) {
+    CodeReviewCommit currentTip =
+        mergeTip != null ? mergeTip.getCurrentTip() : null;
+    if (branchTip == currentTip) {
       logDebug("Branch already at merge tip {}, no update to perform",
-          mergeTip.name());
+          currentTip.name());
       return null;
-    } else if (mergeTip == null) {
+    } else if (currentTip == null) {
       logDebug("No merge tip, no update to perform");
       return null;
     }
@@ -664,17 +667,17 @@ public class MergeOp {
       try {
         ProjectConfig cfg =
             new ProjectConfig(destProject.getProject().getNameKey());
-        cfg.load(repo, mergeTip);
+        cfg.load(repo, currentTip);
       } catch (Exception e) {
         throw new MergeException("Submit would store invalid"
-            + " project configuration " + mergeTip.name() + " for "
+            + " project configuration " + currentTip.name() + " for "
             + destProject.getProject().getName(), e);
       }
     }
 
     branchUpdate.setRefLogIdent(refLogIdent);
     branchUpdate.setForceUpdate(false);
-    branchUpdate.setNewObjectId(mergeTip);
+    branchUpdate.setNewObjectId(currentTip);
     branchUpdate.setRefLogMessage("merged", true);
     try {
       RefUpdate.Result result = branchUpdate.update(rw);
@@ -688,7 +691,7 @@ public class MergeOp {
             tagCache.updateFastForward(destBranch.getParentKey(),
                 branchUpdate.getName(),
                 branchUpdate.getOldObjectId(),
-                mergeTip);
+                currentTip);
           }
 
           if (RefNames.REFS_CONFIG.equals(branchUpdate.getName())) {
@@ -722,7 +725,8 @@ public class MergeOp {
   private void fireRefUpdated(RefUpdate branchUpdate) {
     logDebug("Firing ref updated hooks for {}", branchUpdate.getName());
     gitRefUpdated.fire(destBranch.getParentKey(), branchUpdate);
-    hooks.doRefUpdatedHook(destBranch, branchUpdate, getAccount(mergeTip));
+    hooks.doRefUpdatedHook(destBranch, branchUpdate,
+        getAccount(mergeTip.getCurrentTip()));
   }
 
   private Account getAccount(CodeReviewCommit codeReviewCommit) {
@@ -743,7 +747,7 @@ public class MergeOp {
     return "";
   }
 
-  private void updateChangeStatus(List<Change> submitted)
+  private void updateChangeStatus(List<Change> submitted, MergeTip mergeTip)
       throws NoSuchChangeException {
     logDebug("Updating change status for {} changes", submitted.size());
     for (Change c : submitted) {
@@ -761,21 +765,25 @@ public class MergeOp {
       String txt = s.getMessage();
       logDebug("Status of change {} ({}) on {}: {}", c.getId(), commit.name(),
           c.getDest(), s);
-
+      String commitName = commit.getName();
+      // If mergeTip is null merge failed and mergeResultRev will not be read.
+      String mergeResultRev =
+          mergeTip != null ? mergeTip.getMergeResults().get(commitName) : null;
       try {
         switch (s) {
           case CLEAN_MERGE:
-            setMerged(c, message(c, txt + getByAccountName(commit)));
+            setMerged(c, message(c, txt + getByAccountName(commit)),
+                mergeResultRev);
             break;
 
           case CLEAN_REBASE:
           case CLEAN_PICK:
             setMerged(c, message(c, txt + " as " + commit.name()
-                + getByAccountName(commit)));
+                + getByAccountName(commit)), mergeResultRev);
             break;
 
           case ALREADY_MERGED:
-            setMerged(c, null);
+            setMerged(c, null, mergeResultRev);
             break;
 
           case PATH_CONFLICT:
@@ -810,13 +818,14 @@ public class MergeOp {
   }
 
   private void updateSubscriptions(List<Change> submitted) {
-    if (mergeTip != null && (branchTip == null || branchTip != mergeTip)) {
+    if (mergeTip != null
+        && (branchTip == null || branchTip != mergeTip.getCurrentTip())) {
       logDebug("Updating submodule subscriptions for {} changes",
           submitted.size());
       SubmoduleOp subOp =
-          subOpFactory.create(destBranch, mergeTip, rw, repo,
+          subOpFactory.create(destBranch, mergeTip.getCurrentTip(), rw, repo,
               destProject.getProject(), submitted, commits,
-              getAccount(mergeTip));
+              getAccount(mergeTip.getCurrentTip()));
       try {
         subOp.update();
       } catch (SubmoduleException e) {
@@ -928,7 +937,7 @@ public class MergeOp {
     return m;
   }
 
-  private void setMerged(Change c, ChangeMessage msg)
+  private void setMerged(Change c, ChangeMessage msg, String mergeResultRev)
       throws OrmException, IOException {
     logDebug("Setting change {} merged", c.getId());
     ChangeUpdate update = null;
@@ -954,6 +963,7 @@ public class MergeOp {
         cmUtil.addChangeMessage(db, update, msg);
       }
       db.commit();
+
     } finally {
       db.rollback();
     }
@@ -964,7 +974,7 @@ public class MergeOp {
       try {
         hooks.doChangeMergedHook(c,
             accountCache.get(submitter.getAccountId()).getAccount(),
-            merged, db);
+            merged, db, mergeResultRev);
       } catch (OrmException ex) {
         logError("Cannot run hook for submitted patch set " + c.getId(), ex);
       }

gerrit-server/src/main/java/com/google/gerrit/server/git/MergeTip.java

@@ -0,0 +1,70 @@
+// Copyright (C) 2014 The Android Open Source Project
+//
+// 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.gerrit.server.git;
+
+import com.google.common.collect.Maps;
+
+import java.util.Collection;
+import java.util.Map;
+
+/**
+ * Class describing a merge tip during merge operation.
+ */
+public class MergeTip {
+  private CodeReviewCommit branchTip;
+  private Map<String,String> mergeResults;
+
+  /**
+   * @param initial Tip before the merge operation.
+   * @param toMerge List of CodeReview commits to be merged in merge operation.
+   */
+  public MergeTip(CodeReviewCommit initial, Collection<CodeReviewCommit> toMerge) {
+    this.mergeResults = Maps.newHashMap();
+    this.branchTip = initial;
+    // Assume fast-forward merge until opposite is proven.
+    for (CodeReviewCommit commit : toMerge) {
+      mergeResults.put(commit.getName(), commit.getName());
+    }
+  }
+
+  /**
+   * Moves this MergeTip to newTip and appends mergeResult.
+   *
+   * @param newTip The new tip
+   * @param mergedFrom The result of the merge of newTip
+   */
+  public void moveTipTo(CodeReviewCommit newTip, String mergedFrom) {
+    branchTip = newTip;
+    mergeResults.put(mergedFrom, newTip.getName());
+  }
+
+  /**
+   * The merge results of all the merges of this merge operation.
+   *
+   * @return The merge results of the merge operation Map<<sha1 of the commit to
+   *         be merged>, <sha1 of the merge result>>
+   */
+  public Map<String, String> getMergeResults() {
+    return this.mergeResults;
+  }
+
+  /**
+   *
+   * @return The current tip of the current merge operation.
+   */
+  public CodeReviewCommit getCurrentTip() {
+    return branchTip;
+  }
+}

gerrit-server/src/main/java/com/google/gerrit/server/git/ReceiveCommits.java

@@ -2147,7 +2147,7 @@ public class ReceiveCommits {
       hooks.doPatchsetCreatedHook(change, newPatchSet, db);
       if (mergedIntoRef != null) {
         hooks.doChangeMergedHook(
-            change, currentUser.getAccount(), newPatchSet, db);
+            change, currentUser.getAccount(), newPatchSet, db, newCommit.getName());
       }
 
       if (magicBranch != null && magicBranch.submit) {
@@ -2434,7 +2434,7 @@ public class ReceiveCommits {
     result.mergedIntoRef = refName;
     markChangeMergedByPush(db, result, result.changeCtl);
     hooks.doChangeMergedHook(
-        change, currentUser.getAccount(), result.newPatchSet, db);
+        change, currentUser.getAccount(), result.newPatchSet, db, commit.getName());
     sendMergedEmail(result);
     return change.getKey();
   }

gerrit-server/src/main/java/com/google/gerrit/server/git/strategy/CherryPick.java

@@ -30,6 +30,7 @@ import com.google.gerrit.server.git.CommitMergeStatus;
 import com.google.gerrit.server.git.MergeConflictException;
 import com.google.gerrit.server.git.MergeException;
 import com.google.gerrit.server.git.MergeIdenticalTreeException;
+import com.google.gerrit.server.git.MergeTip;
 import com.google.gerrit.server.patch.PatchSetInfoFactory;
 import com.google.gerrit.server.project.NoSuchChangeException;
 import com.google.gwtorm.server.OrmException;
@@ -63,18 +64,20 @@ public class CherryPick extends SubmitStrategy {
   }
 
   @Override
-  protected CodeReviewCommit _run(CodeReviewCommit mergeTip,
+  protected MergeTip _run(CodeReviewCommit branchTip,
       Collection<CodeReviewCommit> toMerge) throws MergeException {
-    List<CodeReviewCommit> sorted = CodeReviewCommit.ORDER.sortedCopy(toMerge);
+    MergeTip mergeTip =
-    while (!sorted.isEmpty()) {
+        branchTip != null ? new MergeTip(branchTip, toMerge)
-      CodeReviewCommit n = sorted.remove(0);
+            : null;
-
+        List<CodeReviewCommit> sorted = CodeReviewCommit.ORDER.sortedCopy(toMerge);
+        while (!sorted.isEmpty()) {
+          CodeReviewCommit n = sorted.remove(0);
       try {
         if (mergeTip == null) {
           // The branch is unborn. Take a fast-forward resolution to
           // create the branch.
           //
-          mergeTip = n;
+          mergeTip = new MergeTip(n, Lists.newArrayList(n));
           n.setStatusCode(CommitMergeStatus.CLEAN_MERGE);
 
         } else if (n.getParentCount() == 0) {
@@ -89,8 +92,10 @@ public class CherryPick extends SubmitStrategy {
           // that on the current merge tip.
           //
           try {
-            mergeTip = writeCherryPickCommit(mergeTip, n);
+            CodeReviewCommit merge = writeCherryPickCommit(mergeTip.getCurrentTip(), n);
-            newCommits.put(mergeTip.getPatchsetId().getParentKey(), mergeTip);
+            mergeTip.moveTipTo(merge, merge.getName());
+            newCommits.put(mergeTip.getCurrentTip().getPatchsetId()
+                .getParentKey(), mergeTip.getCurrentTip());
           } catch (MergeConflictException mce) {
             n.setStatusCode(CommitMergeStatus.PATH_CONFLICT);
             mergeTip = null;
@@ -106,15 +111,17 @@ public class CherryPick extends SubmitStrategy {
           // instead behave as though MERGE_IF_NECESSARY was configured.
           //
           if (!args.mergeUtil.hasMissingDependencies(args.mergeSorter, n)) {
-            if (args.rw.isMergedInto(mergeTip, n)) {
+            if (args.rw.isMergedInto(mergeTip.getCurrentTip(), n)) {
-              mergeTip = n;
+              mergeTip.moveTipTo(n, n.getName());
             } else {
-              mergeTip = args.mergeUtil.mergeOneCommit(args.serverIdent.get(),
+              mergeTip.moveTipTo(
-                  args.repo, args.rw, args.inserter, args.canMergeFlag,
+                  args.mergeUtil.mergeOneCommit(args.serverIdent.get(), args.repo,
-                  args.destBranch, mergeTip, n);
+                      args.rw, args.inserter, args.canMergeFlag,
-            }
+                      args.destBranch, mergeTip.getCurrentTip(), n), n.getName());
-            PatchSetApproval submitApproval = args.mergeUtil.markCleanMerges(
+           }
-                args.rw, args.canMergeFlag, mergeTip, args.alreadyAccepted);
+            final PatchSetApproval submitApproval =
+                args.mergeUtil.markCleanMerges(args.rw, args.canMergeFlag,
+                    mergeTip.getCurrentTip(), args.alreadyAccepted);
             setRefLogIdent(submitApproval);
           } else {
             // One or more dependencies were not met. The status was

gerrit-server/src/main/java/com/google/gerrit/server/git/strategy/FastForwardOnly.java

@@ -18,6 +18,7 @@ import com.google.gerrit.reviewdb.client.PatchSetApproval;
 import com.google.gerrit.server.git.CodeReviewCommit;
 import com.google.gerrit.server.git.CommitMergeStatus;
 import com.google.gerrit.server.git.MergeException;
+import com.google.gerrit.server.git.MergeTip;
 
 import java.util.Collection;
 import java.util.List;
@@ -28,23 +29,26 @@ public class FastForwardOnly extends SubmitStrategy {
   }
 
   @Override
-  protected CodeReviewCommit _run(CodeReviewCommit mergeTip,
+  protected MergeTip _run(final CodeReviewCommit branchTip,
-      Collection<CodeReviewCommit> toMerge) throws MergeException {
+      final Collection<CodeReviewCommit> toMerge) throws MergeException {
+    MergeTip mergeTip = new MergeTip(branchTip, toMerge);
     List<CodeReviewCommit> sorted = args.mergeUtil.reduceToMinimalMerge(
         args.mergeSorter, toMerge);
-    CodeReviewCommit newMergeTip =
+    final CodeReviewCommit newMergeTipCommit =
-        args.mergeUtil.getFirstFastForward(mergeTip, args.rw, sorted);
+        args.mergeUtil.getFirstFastForward(branchTip, args.rw, sorted);
+    mergeTip.moveTipTo(newMergeTipCommit, newMergeTipCommit.getName());
 
     while (!sorted.isEmpty()) {
-      CodeReviewCommit n = sorted.remove(0);
+      final CodeReviewCommit n = sorted.remove(0);
       n.setStatusCode(CommitMergeStatus.NOT_FAST_FORWARD);
     }
 
-    PatchSetApproval submitApproval = args.mergeUtil.markCleanMerges(args.rw,
+    PatchSetApproval submitApproval =
-        args.canMergeFlag, newMergeTip, args.alreadyAccepted);
+        args.mergeUtil.markCleanMerges(args.rw, args.canMergeFlag, newMergeTipCommit,
+            args.alreadyAccepted);
     setRefLogIdent(submitApproval);
 
-    return newMergeTip;
+    return mergeTip;
   }
 
   @Override

gerrit-server/src/main/java/com/google/gerrit/server/git/strategy/MergeAlways.java

@@ -17,6 +17,7 @@ package com.google.gerrit.server.git.strategy;
 import com.google.gerrit.reviewdb.client.PatchSetApproval;
 import com.google.gerrit.server.git.CodeReviewCommit;
 import com.google.gerrit.server.git.MergeException;
+import com.google.gerrit.server.git.MergeTip;
 
 import java.util.Collection;
 import java.util.List;
@@ -27,24 +28,29 @@ public class MergeAlways extends SubmitStrategy {
   }
 
   @Override
-  protected CodeReviewCommit _run(CodeReviewCommit mergeTip,
+  protected MergeTip _run(CodeReviewCommit branchTip,
       Collection<CodeReviewCommit> toMerge) throws MergeException {
-    List<CodeReviewCommit> sorted = args.mergeUtil.reduceToMinimalMerge(
+  List<CodeReviewCommit> sorted = args.mergeUtil.reduceToMinimalMerge(args.mergeSorter, toMerge);
-        args.mergeSorter, toMerge);
+    MergeTip mergeTip;
-
+    if (branchTip == null) {
-    if (mergeTip == null) {
       // The branch is unborn. Take a fast-forward resolution to
       // create the branch.
-      mergeTip = sorted.remove(0);
+      mergeTip = new MergeTip(sorted.get(0), toMerge);
+      sorted.remove(0);
+    } else {
+      mergeTip = new MergeTip(branchTip, toMerge);
     }
     while (!sorted.isEmpty()) {
-      mergeTip = args.mergeUtil.mergeOneCommit(args.serverIdent.get(),
+      CodeReviewCommit mergedFrom = sorted.remove(0);
-          args.repo, args.rw, args.inserter, args.canMergeFlag, args.destBranch,
+      CodeReviewCommit newTip =
-          mergeTip, sorted.remove(0));
+          args.mergeUtil.mergeOneCommit(args.serverIdent.get(), args.repo, args.rw,
+              args.inserter, args.canMergeFlag, args.destBranch, mergeTip.getCurrentTip(),
+              mergedFrom);
+      mergeTip.moveTipTo(newTip, mergedFrom.getName());
     }
 
-    PatchSetApproval submitApproval =
+    final PatchSetApproval submitApproval =
-        args.mergeUtil.markCleanMerges(args.rw, args.canMergeFlag, mergeTip,
+        args.mergeUtil.markCleanMerges(args.rw, args.canMergeFlag, mergeTip.getCurrentTip(),
             args.alreadyAccepted);
     setRefLogIdent(submitApproval);
 

gerrit-server/src/main/java/com/google/gerrit/server/git/strategy/MergeIfNecessary.java

@@ -17,6 +17,7 @@ package com.google.gerrit.server.git.strategy;
 import com.google.gerrit.reviewdb.client.PatchSetApproval;
 import com.google.gerrit.server.git.CodeReviewCommit;
 import com.google.gerrit.server.git.MergeException;
+import com.google.gerrit.server.git.MergeTip;
 
 import java.util.Collection;
 import java.util.List;
@@ -27,29 +28,36 @@ public class MergeIfNecessary extends SubmitStrategy {
   }
 
   @Override
-  protected CodeReviewCommit _run(CodeReviewCommit mergeTip,
+  protected MergeTip _run(CodeReviewCommit branchTip,
       Collection<CodeReviewCommit> toMerge) throws MergeException {
-    List<CodeReviewCommit> sorted = args.mergeUtil.reduceToMinimalMerge(
+    List<CodeReviewCommit> sorted =
-        args.mergeSorter, toMerge);
+        args.mergeUtil.reduceToMinimalMerge(args.mergeSorter, toMerge);
-
+    MergeTip mergeTip;
-    if (mergeTip == null) {
+    if (branchTip == null) {
       // The branch is unborn. Take a fast-forward resolution to
       // create the branch.
-      mergeTip = sorted.remove(0);
+      mergeTip = new MergeTip(sorted.get(0), toMerge);
+      branchTip = sorted.remove(0);
+    } else {
+      mergeTip = new MergeTip(branchTip, toMerge);
+      branchTip =
+          args.mergeUtil.getFirstFastForward(branchTip, args.rw, sorted);
     }
-
+    mergeTip.moveTipTo(branchTip, branchTip.getName());
-    mergeTip =
-        args.mergeUtil.getFirstFastForward(mergeTip, args.rw, sorted);
 
     // For every other commit do a pair-wise merge.
     while (!sorted.isEmpty()) {
-      mergeTip = args.mergeUtil.mergeOneCommit(args.serverIdent.get(),
+      CodeReviewCommit mergedFrom = sorted.remove(0);
-          args.repo, args.rw, args.inserter, args.canMergeFlag, args.destBranch,
+      branchTip =
-          mergeTip, sorted.remove(0));
+          args.mergeUtil.mergeOneCommit(args.serverIdent.get(), args.repo,
+              args.rw, args.inserter, args.canMergeFlag, args.destBranch,
+              branchTip, mergedFrom);
+      mergeTip.moveTipTo(branchTip, mergedFrom.getName());
     }
 
-    PatchSetApproval submitApproval = args.mergeUtil.markCleanMerges(
+    final PatchSetApproval submitApproval =
-        args.rw, args.canMergeFlag, mergeTip, args.alreadyAccepted);
+        args.mergeUtil.markCleanMerges(args.rw, args.canMergeFlag, branchTip,
+            args.alreadyAccepted);
     setRefLogIdent(submitApproval);
 
     return mergeTip;

gerrit-server/src/main/java/com/google/gerrit/server/git/strategy/RebaseIfNecessary.java

@@ -25,6 +25,7 @@ import com.google.gerrit.server.git.CodeReviewCommit;
 import com.google.gerrit.server.git.CommitMergeStatus;
 import com.google.gerrit.server.git.MergeConflictException;
 import com.google.gerrit.server.git.MergeException;
+import com.google.gerrit.server.git.MergeTip;
 import com.google.gerrit.server.git.RebaseSorter;
 import com.google.gerrit.server.patch.PatchSetInfoFactory;
 import com.google.gerrit.server.project.InvalidChangeOperationException;
@@ -55,20 +56,19 @@ public class RebaseIfNecessary extends SubmitStrategy {
   }
 
   @Override
-  protected CodeReviewCommit _run(CodeReviewCommit mergeTip,
+  protected MergeTip _run(final CodeReviewCommit branchTip,
-      Collection<CodeReviewCommit> toMerge) throws MergeException {
+      final Collection<CodeReviewCommit> toMerge) throws MergeException {
-    CodeReviewCommit newMergeTip = mergeTip;
+    MergeTip mergeTip = new MergeTip(branchTip, toMerge);
     List<CodeReviewCommit> sorted = sort(toMerge);
-
     while (!sorted.isEmpty()) {
       CodeReviewCommit n = sorted.remove(0);
 
-      if (newMergeTip == null) {
+      if (mergeTip.getCurrentTip() == null) {
         // The branch is unborn. Take a fast-forward resolution to
         // create the branch.
         //
-        newMergeTip = n;
         n.setStatusCode(CommitMergeStatus.CLEAN_MERGE);
+        mergeTip.moveTipTo(n, n.getName());
 
       } else if (n.getParentCount() == 0) {
         // Refuse to merge a root commit into an existing branch,
@@ -77,37 +77,44 @@ public class RebaseIfNecessary extends SubmitStrategy {
         n.setStatusCode(CommitMergeStatus.CANNOT_REBASE_ROOT);
 
       } else if (n.getParentCount() == 1) {
-        if (args.mergeUtil.canFastForward(
+        if (args.mergeUtil.canFastForward(args.mergeSorter,
-            args.mergeSorter, newMergeTip, args.rw, n)) {
+            mergeTip.getCurrentTip(), args.rw, n)) {
-          newMergeTip = n;
           n.setStatusCode(CommitMergeStatus.CLEAN_MERGE);
+          mergeTip.moveTipTo(n, n.getName());
 
         } else {
           try {
-            IdentifiedUser uploader = args.identifiedUserFactory.create(
+            IdentifiedUser uploader =
-                args.mergeUtil.getSubmitter(n).getAccountId());
+                args.identifiedUserFactory.create(args.mergeUtil
-            PatchSet newPatchSet = rebaseChange.rebase(args.repo, args.rw,
+                    .getSubmitter(n).getAccountId());
-                args.inserter, n.getPatchsetId(), n.change(), uploader,
+            PatchSet newPatchSet =
-                newMergeTip, args.mergeUtil, args.serverIdent.get(), false,
+                rebaseChange.rebase(args.repo, args.rw, args.inserter,
-                false, ValidatePolicy.NONE);
+                    n.getPatchsetId(), n.change(), uploader,
+                    mergeTip.getCurrentTip(), args.mergeUtil,
+                    args.serverIdent.get(), false, false, ValidatePolicy.NONE);
 
             List<PatchSetApproval> approvals = Lists.newArrayList();
-            for (PatchSetApproval a : args.approvalsUtil.byPatchSet(
+            for (PatchSetApproval a : args.approvalsUtil.byPatchSet(args.db,
-                args.db, n.getControl(), n.getPatchsetId())) {
+                n.getControl(), n.getPatchsetId())) {
               approvals.add(new PatchSetApproval(newPatchSet.getId(), a));
             }
             // rebaseChange.rebase() may already have copied some approvals,
             // use upsert, not insert, to avoid constraint violation on database
             args.db.patchSetApprovals().upsert(approvals);
-            newMergeTip = (CodeReviewCommit) args.rw.parseCommit(
+            mergeTip.moveTipTo((CodeReviewCommit) args.rw.parseCommit(ObjectId
-                ObjectId.fromString(newPatchSet.getRevision().get()));
+                .fromString(newPatchSet.getRevision().get())), newPatchSet
+                .getRevision().get());
             n.change().setCurrentPatchSet(
-                patchSetInfoFactory.get(newMergeTip, newPatchSet.getId()));
+                patchSetInfoFactory.get(mergeTip.getCurrentTip(),
-            newMergeTip.copyFrom(n);
+                    newPatchSet.getId()));
-            newMergeTip.setControl(args.changeControlFactory.controlFor(n.change(), uploader));
+            mergeTip.getCurrentTip().copyFrom(n);
-            newMergeTip.setPatchsetId(newPatchSet.getId());
+            mergeTip.getCurrentTip().setControl(
-            newMergeTip.setStatusCode(CommitMergeStatus.CLEAN_REBASE);
+                args.changeControlFactory.controlFor(n.change(), uploader));
-            newCommits.put(newPatchSet.getId().getParentKey(), newMergeTip);
+            mergeTip.getCurrentTip().setPatchsetId(newPatchSet.getId());
+            mergeTip.getCurrentTip().setStatusCode(
+                CommitMergeStatus.CLEAN_REBASE);
+            newCommits.put(newPatchSet.getId().getParentKey(),
+                mergeTip.getCurrentTip());
             setRefLogIdent(args.mergeUtil.getSubmitter(n));
           } catch (MergeConflictException e) {
             n.setStatusCode(CommitMergeStatus.REBASE_MERGE_CONFLICT);
@@ -125,25 +132,27 @@ public class RebaseIfNecessary extends SubmitStrategy {
         // instead behave as though MERGE_IF_NECESSARY was configured.
         //
         try {
-          if (args.rw.isMergedInto(newMergeTip, n)) {
+          if (args.rw.isMergedInto(mergeTip.getCurrentTip(), n)) {
-            newMergeTip = n;
+            mergeTip.moveTipTo(n, n.getName());
           } else {
-            newMergeTip = args.mergeUtil.mergeOneCommit(
+            mergeTip.moveTipTo(
-                args.serverIdent.get(), args.repo, args.rw, args.inserter,
+                args.mergeUtil.mergeOneCommit(args.serverIdent.get(),
-                args.canMergeFlag, args.destBranch, newMergeTip, n);
+                    args.repo, args.rw, args.inserter, args.canMergeFlag,
+                    args.destBranch, mergeTip.getCurrentTip(), n), n.getName());
           }
-          PatchSetApproval submitApproval = args.mergeUtil.markCleanMerges(
+          PatchSetApproval submitApproval =
-              args.rw, args.canMergeFlag, newMergeTip, args.alreadyAccepted);
+              args.mergeUtil.markCleanMerges(args.rw, args.canMergeFlag,
+                  mergeTip.getCurrentTip(), args.alreadyAccepted);
           setRefLogIdent(submitApproval);
         } catch (IOException e) {
           throw new MergeException("Cannot merge " + n.name(), e);
         }
       }
 
-      args.alreadyAccepted.add(newMergeTip);
+      args.alreadyAccepted.add(mergeTip.getCurrentTip());
     }
 
-    return newMergeTip;
+    return mergeTip;
   }
 
   private List<CodeReviewCommit> sort(Collection<CodeReviewCommit> toSort)

gerrit-server/src/main/java/com/google/gerrit/server/git/strategy/SubmitStrategy.java

@@ -24,6 +24,7 @@ import com.google.gerrit.server.IdentifiedUser;
 import com.google.gerrit.server.git.CodeReviewCommit;
 import com.google.gerrit.server.git.MergeException;
 import com.google.gerrit.server.git.MergeSorter;
+import com.google.gerrit.server.git.MergeTip;
 import com.google.gerrit.server.git.MergeUtil;
 import com.google.gerrit.server.index.ChangeIndexer;
 import com.google.gerrit.server.project.ChangeControl;
@@ -104,21 +105,21 @@ public abstract class SubmitStrategy {
    * <p>
    * If possible, the provided commits will be merged with this submit strategy.
    *
-   * @param mergeTip the merge tip.
+   * @param currentTip the mergeTip
    * @param toMerge the list of submitted commits that should be merged using
    *        this submit strategy. Implementations are responsible for ordering
    *        of commits, and should not modify the input in place.
    * @return the new merge tip.
    * @throws MergeException
    */
-  public CodeReviewCommit run(CodeReviewCommit mergeTip,
+  public final MergeTip run(final CodeReviewCommit currentTip,
-      Collection<CodeReviewCommit> toMerge) throws MergeException {
+      final Collection<CodeReviewCommit> toMerge) throws MergeException {
     refLogIdent = null;
-    return _run(mergeTip, toMerge);
+    return _run(currentTip, toMerge);
   }
 
   /** @see #run(CodeReviewCommit, Collection) */
-  protected abstract CodeReviewCommit _run(CodeReviewCommit mergeTip,
+  protected abstract MergeTip _run(CodeReviewCommit currentTip,
       Collection<CodeReviewCommit> toMerge) throws MergeException;
 
   /**