Cherry-pick: Differentiate between conflicts and already merged errors

When cherry-pick operation fails with "Cherry pick failed" error, there
is no way to know the reason for the failure: merge conflict or the
commit is already on the target branch.  Differentiate between these
failures and report the proper result to the client.

Change-Id: If1139e3c13623fb98a9584e4e399cfdf45fd3613

gerrit-acceptance-tests/src/test/java/com/google/gerrit/acceptance/api/revision/RevisionIT.java

@@ -17,6 +17,7 @@ package com.google.gerrit.acceptance.api.revision;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.fail;
 
 import com.google.common.collect.Iterables;
 import com.google.gerrit.acceptance.AbstractDaemonTest;
@@ -145,10 +146,67 @@ public class RevisionIT extends AbstractDaemonTest {
     assertEquals(2, orig.get().messages.size());
 
     assertTrue(cherry.get().subject.contains(in.message));
-    cherry.current()
+    cherry.current().review(ReviewInput.approve());
-        .review(ReviewInput.approve());
+    cherry.current().submit();
-    cherry.current()
+  }
-        .submit();
+
+  @Test
+  public void cherryPickIdenticalTree() throws GitAPIException,
+      IOException, RestApiException {
+    PushOneCommit.Result r = createChange();
+    CherryPickInput in = new CherryPickInput();
+    in.destination = "foo";
+    in.message = "it goes to stable branch";
+    gApi.projects()
+        .name(project.get())
+        .branch(in.destination)
+        .create(new BranchInput());
+    ChangeApi orig = gApi.changes()
+        .id("p~master~" + r.getChangeId());
+
+    assertEquals(1, orig.get().messages.size());
+    ChangeApi cherry = orig.revision(r.getCommit().name())
+        .cherryPick(in);
+    assertEquals(2, orig.get().messages.size());
+
+    assertTrue(cherry.get().subject.contains(in.message));
+    cherry.current().review(ReviewInput.approve());
+    cherry.current().submit();
+
+    try {
+      orig.revision(r.getCommit().name()).cherryPick(in);
+      fail("Cherry-pick identical tree error expected");
+    } catch (RestApiException e) {
+      assertEquals("Cherry pick failed: identical tree", e.getMessage());
+    }
+  }
+
+  @Test
+  public void cherryPickConflict() throws GitAPIException,
+      IOException, RestApiException {
+    PushOneCommit.Result r = createChange();
+    CherryPickInput in = new CherryPickInput();
+    in.destination = "foo";
+    in.message = "it goes to stable branch";
+    gApi.projects()
+        .name(project.get())
+        .branch(in.destination)
+        .create(new BranchInput());
+
+    PushOneCommit push =
+        pushFactory.create(db, admin.getIdent(), PushOneCommit.SUBJECT,
+            PushOneCommit.FILE_NAME, "another content");
+    push.to(git, "refs/heads/foo");
+
+    ChangeApi orig = gApi.changes().id("p~master~" + r.getChangeId());
+    assertEquals(1, orig.get().messages.size());
+
+    try {
+      orig.revision(r.getCommit().name()).cherryPick(in);
+      fail("Cherry-pick merge conflict error expected");
+    } catch (RestApiException e) {
+      assertEquals("Cherry pick failed: merge conflict", e.getMessage());
+    }
   }
 
   @Test

gerrit-server/src/main/java/com/google/gerrit/server/change/CherryPick.java

@@ -91,7 +91,7 @@ public class CherryPick implements RestModifyView<RevisionResource, CherryPickIn
       return json.format(cherryPickedChangeId);
     } catch (InvalidChangeOperationException e) {
       throw new BadRequestException(e.getMessage());
-    } catch (MergeException  e) {
+    } catch (MergeException e) {
       throw new ResourceConflictException(e.getMessage());
     } catch (NoSuchChangeException e) {
       throw new ResourceNotFoundException(e.getMessage());

gerrit-server/src/main/java/com/google/gerrit/server/change/CherryPickChange.java

@@ -27,7 +27,9 @@ import com.google.gerrit.server.GerritPersonIdent;
 import com.google.gerrit.server.IdentifiedUser;
 import com.google.gerrit.server.events.CommitReceivedEvent;
 import com.google.gerrit.server.git.GitRepositoryManager;
+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.MergeUtil;
 import com.google.gerrit.server.git.validators.CommitValidationException;
 import com.google.gerrit.server.git.validators.CommitValidators;
@@ -153,14 +155,12 @@ public class CherryPickChange {
           cherryPickCommit =
               mergeUtilFactory.create(projectState).createCherryPickFromCommit(git, oi, mergeTip,
                   commitToCherryPick, committerIdent, commitMessage, revWalk);
+        } catch (MergeIdenticalTreeException | MergeConflictException e) {
+          throw new MergeException("Cherry pick failed: " + e.getMessage());
         } finally {
           oi.release();
         }
 
-        if (cherryPickCommit == null) {
-          throw new MergeException("Cherry pick failed");
-        }
-
         Change.Key changeKey;
         final List<String> idList = cherryPickCommit.getFooterLines(CHANGE_ID);
         if (!idList.isEmpty()) {

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

@@ -0,0 +1,23 @@
+// 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;
+
+/** Indicates that the commit cannot be merged without conflicts. */
+public class MergeConflictException extends Exception {
+  private static final long serialVersionUID = 1L;
+  public MergeConflictException(String msg) {
+    super(msg, null);
+  }
+}

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

@@ -0,0 +1,23 @@
+// 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;
+
+/** Indicates that the commit is already contained in destination banch. */
+public class MergeIdenticalTreeException extends Exception {
+  private static final long serialVersionUID = 1L;
+  public MergeIdenticalTreeException(String msg) {
+    super(msg, null);
+  }
+}

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

@@ -173,7 +173,8 @@ public class MergeUtil {
   public RevCommit createCherryPickFromCommit(Repository repo,
       ObjectInserter inserter, RevCommit mergeTip, RevCommit originalCommit,
       PersonIdent cherryPickCommitterIdent, String commitMsg, RevWalk rw)
-      throws MissingObjectException, IncorrectObjectTypeException, IOException {
+      throws MissingObjectException, IncorrectObjectTypeException, IOException,
+      MergeIdenticalTreeException, MergeConflictException {
 
     final ThreeWayMerger m = newThreeWayMerger(repo, inserter);
 
@@ -181,7 +182,7 @@ public class MergeUtil {
     if (m.merge(mergeTip, originalCommit)) {
       ObjectId tree = m.getResultTreeId();
       if (tree.equals(mergeTip.getTree())) {
-        return null;
+        throw new MergeIdenticalTreeException("identical tree");
       }
 
       CommitBuilder mergeCommit = new CommitBuilder();
@@ -192,7 +193,7 @@ public class MergeUtil {
       mergeCommit.setMessage(commitMsg);
       return rw.parseCommit(commit(inserter, mergeCommit));
     } else {
-      return null;
+      throw new MergeConflictException("merge conflict");
     }
   }
 

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

@@ -26,7 +26,9 @@ import com.google.gerrit.server.IdentifiedUser;
 import com.google.gerrit.server.extensions.events.GitReferenceUpdated;
 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.MergeIdenticalTreeException;
 import com.google.gerrit.server.patch.PatchSetInfoFactory;
 import com.google.gerrit.server.project.NoSuchChangeException;
 import com.google.gerrit.server.util.TimeUtil;
@@ -84,15 +86,16 @@ public class CherryPick extends SubmitStrategy {
           // taking the delta relative to that one parent and redoing
           // that on the current merge tip.
           //
-
+          try {
-          mergeTip = writeCherryPickCommit(mergeTip, n);
+            mergeTip = writeCherryPickCommit(mergeTip, n);
-
-          if (mergeTip != null) {
             newCommits.put(mergeTip.getPatchsetId().getParentKey(), mergeTip);
-          } else {
+          } catch (MergeConflictException mce) {
             n.setStatusCode(CommitMergeStatus.PATH_CONFLICT);
+            mergeTip = null;
+          } catch (MergeIdenticalTreeException mie) {
+            n.setStatusCode(CommitMergeStatus.ALREADY_MERGED);
+            mergeTip = null;
           }
-
         } else {
           // There are multiple parents, so this is a merge commit. We
           // don't want to cherry-pick the merge as clients can't easily
@@ -131,7 +134,8 @@ public class CherryPick extends SubmitStrategy {
 
   private CodeReviewCommit writeCherryPickCommit(CodeReviewCommit mergeTip,
       CodeReviewCommit n) throws IOException, OrmException,
-      NoSuchChangeException {
+      NoSuchChangeException, MergeConflictException,
+      MergeIdenticalTreeException {
 
     args.rw.parseBody(n);
 
@@ -156,10 +160,6 @@ public class CherryPick extends SubmitStrategy {
             args.inserter, mergeTip, n, cherryPickCommitterIdent,
             cherryPickCmtMsg, args.rw);
 
-    if (newCommit == null) {
-        return null;
-    }
-
     PatchSet.Id id =
         ChangeUtil.nextPatchSetId(args.repo, n.change().currentPatchSetId());
     final PatchSet ps = new PatchSet(id);