Add new REST api for creating a merge patch set for change

Previously, we have a new feature that allow creating a new merge change
(C2PS1) by merge a change(C1PS1) into a branch (release). If the
original change (C1) is updated (C1PS2), the merged change also need to
update (C2PS2) with a new merge with the updated change.

master: C1PS1 -> C1PS2
            \       \
release: C2PS1 -> C2PS2

Without this new merge patch set API, user have to abandon the old merge
change(C2PS1) and then create a new merge change (C3PS1).

REST api at `POST /changes/{change-id}/merge` and take a
MergePatchSetInput.

Change-Id: Ia3ba1bc5ff30920d1f8270f4fe28ccd7da7ed2a9

gerrit-server/src/main/java/com/google/gerrit/server/api/changes/ChangeApiImpl.java

@@ -31,6 +31,7 @@ import com.google.gerrit.extensions.api.changes.SubmittedTogetherOption;
 import com.google.gerrit.extensions.client.ListChangesOption;
 import com.google.gerrit.extensions.common.AccountInfo;
 import com.google.gerrit.extensions.common.ChangeInfo;
+import com.google.gerrit.extensions.common.MergePatchSetInput;
 import com.google.gerrit.extensions.common.CommentInfo;
 import com.google.gerrit.extensions.common.EditInfo;
 import com.google.gerrit.extensions.common.SuggestedReviewerInfo;
@@ -63,7 +64,9 @@ import com.google.gerrit.server.change.Reviewers;
 import com.google.gerrit.server.change.Revisions;
 import com.google.gerrit.server.change.SubmittedTogether;
 import com.google.gerrit.server.change.SuggestChangeReviewers;
+import com.google.gerrit.server.change.CreateMergePatchSet;
 import com.google.gerrit.server.git.UpdateException;
+import com.google.gerrit.server.project.InvalidChangeOperationException;
 import com.google.gerrit.server.project.NoSuchChangeException;
 import com.google.gwtorm.server.OrmException;
 import com.google.inject.Inject;
@@ -91,6 +94,7 @@ class ChangeApiImpl implements ChangeApi {
   private final Abandon abandon;
   private final Revert revert;
   private final Restore restore;
+  private final CreateMergePatchSet updateByMerge;
   private final Provider<SubmittedTogether> submittedTogether;
   private final PublishDraftPatchSet.CurrentRevision
     publishDraftChange;
@@ -122,6 +126,7 @@ class ChangeApiImpl implements ChangeApi {
       Abandon abandon,
       Revert revert,
       Restore restore,
+      CreateMergePatchSet updateByMerge,
       Provider<SubmittedTogether> submittedTogether,
       PublishDraftPatchSet.CurrentRevision publishDraftChange,
       DeleteDraftChange deleteDraftChange,
@@ -151,6 +156,7 @@ class ChangeApiImpl implements ChangeApi {
     this.suggestReviewers = suggestReviewers;
     this.abandon = abandon;
     this.restore = restore;
+    this.updateByMerge = updateByMerge;
     this.submittedTogether = submittedTogether;
     this.publishDraftChange = publishDraftChange;
     this.deleteDraftChange = deleteDraftChange;
@@ -267,6 +273,17 @@ class ChangeApiImpl implements ChangeApi {
     }
   }
 
+  @Override
+  public ChangeInfo createMergePatchSet(MergePatchSetInput in)
+      throws RestApiException {
+    try {
+      return updateByMerge.apply(change, in).value();
+    } catch (IOException | UpdateException | InvalidChangeOperationException
+        | NoSuchChangeException | OrmException e) {
+      throw new RestApiException("Cannot update change by merge", e);
+    }
+  }
+
   @Override
   public List<ChangeInfo> submittedTogether() throws RestApiException {
     SubmittedTogetherInfo info = submittedTogether(

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

@@ -0,0 +1,212 @@
+// Copyright (C) 2016 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.change;
+
+import com.google.common.base.MoreObjects;
+import com.google.common.base.Strings;
+import com.google.gerrit.common.TimeUtil;
+import com.google.gerrit.extensions.api.changes.NotifyHandling;
+import com.google.gerrit.extensions.client.ListChangesOption;
+import com.google.gerrit.extensions.common.ChangeInfo;
+import com.google.gerrit.extensions.common.MergePatchSetInput;
+import com.google.gerrit.extensions.common.MergeInput;
+import com.google.gerrit.extensions.restapi.AuthException;
+import com.google.gerrit.extensions.restapi.BadRequestException;
+import com.google.gerrit.extensions.restapi.MergeConflictException;
+import com.google.gerrit.extensions.restapi.ResourceNotFoundException;
+import com.google.gerrit.extensions.restapi.Response;
+import com.google.gerrit.extensions.restapi.RestApiException;
+import com.google.gerrit.extensions.restapi.RestModifyView;
+import com.google.gerrit.reviewdb.client.Branch;
+import com.google.gerrit.reviewdb.client.Change;
+import com.google.gerrit.reviewdb.client.PatchSet;
+import com.google.gerrit.reviewdb.client.Project;
+import com.google.gerrit.reviewdb.server.ReviewDb;
+import com.google.gerrit.server.ChangeUtil;
+import com.google.gerrit.server.CurrentUser;
+import com.google.gerrit.server.GerritPersonIdent;
+import com.google.gerrit.server.IdentifiedUser;
+import com.google.gerrit.server.PatchSetUtil;
+import com.google.gerrit.server.git.BatchUpdate;
+import com.google.gerrit.server.git.GitRepositoryManager;
+import com.google.gerrit.server.git.MergeIdenticalTreeException;
+import com.google.gerrit.server.git.MergeUtil;
+import com.google.gerrit.server.git.UpdateException;
+import com.google.gerrit.server.project.ChangeControl;
+import com.google.gerrit.server.project.InvalidChangeOperationException;
+import com.google.gerrit.server.project.NoSuchChangeException;
+import com.google.gerrit.server.project.ProjectControl;
+import com.google.gwtorm.server.OrmException;
+import com.google.inject.Inject;
+import com.google.inject.Provider;
+import com.google.inject.Singleton;
+
+import org.eclipse.jgit.lib.ObjectId;
+import org.eclipse.jgit.lib.ObjectInserter;
+import org.eclipse.jgit.lib.PersonIdent;
+import org.eclipse.jgit.lib.Ref;
+import org.eclipse.jgit.lib.Repository;
+import org.eclipse.jgit.revwalk.RevCommit;
+import org.eclipse.jgit.revwalk.RevWalk;
+import org.eclipse.jgit.util.ChangeIdUtil;
+
+import java.io.IOException;
+import java.sql.Timestamp;
+import java.util.EnumSet;
+import java.util.TimeZone;
+
+@Singleton
+public class CreateMergePatchSet implements
+    RestModifyView<ChangeResource, MergePatchSetInput> {
+
+  private final Provider<ReviewDb> db;
+  private final GitRepositoryManager gitManager;
+  private final TimeZone serverTimeZone;
+  private final Provider<CurrentUser> user;
+  private final ChangeJson.Factory jsonFactory;
+  private final PatchSetUtil psUtil;
+  private final MergeUtil.Factory mergeUtilFactory;
+  private final BatchUpdate.Factory batchUpdateFactory;
+  private final PatchSetInserter.Factory patchSetInserterFactory;
+
+  @Inject
+  CreateMergePatchSet(Provider<ReviewDb> db,
+      GitRepositoryManager gitManager,
+      @GerritPersonIdent PersonIdent myIdent,
+      Provider<CurrentUser> user,
+      ChangeJson.Factory json,
+      PatchSetUtil psUtil,
+      MergeUtil.Factory mergeUtilFactory,
+      BatchUpdate.Factory batchUpdateFactory,
+      PatchSetInserter.Factory patchSetInserterFactory) {
+    this.db = db;
+    this.gitManager = gitManager;
+    this.serverTimeZone = myIdent.getTimeZone();
+    this.user = user;
+    this.jsonFactory = json;
+    this.psUtil = psUtil;
+    this.mergeUtilFactory = mergeUtilFactory;
+    this.batchUpdateFactory = batchUpdateFactory;
+    this.patchSetInserterFactory = patchSetInserterFactory;
+  }
+
+  @Override
+  public Response<ChangeInfo> apply(ChangeResource req, MergePatchSetInput in)
+      throws NoSuchChangeException, OrmException, IOException,
+      InvalidChangeOperationException, RestApiException, UpdateException {
+    if (in.merge == null) {
+      throw new BadRequestException("merge field is required");
+    }
+
+    MergeInput merge = in.merge;
+    if (Strings.isNullOrEmpty(merge.source)) {
+      throw new BadRequestException("merge.source must be non-empty");
+    }
+
+    ChangeControl ctl = req.getControl();
+    if (!ctl.isVisible(db.get())) {
+      throw new InvalidChangeOperationException(
+          "Base change not found: " + req.getId());
+    }
+    PatchSet ps = psUtil.current(db.get(), ctl.getNotes());
+    if (!ctl.canAddPatchSet(db.get())) {
+      throw new AuthException("cannot add patch set");
+    }
+
+    ProjectControl projectControl = ctl.getProjectControl();
+    Change change = ctl.getChange();
+    Project.NameKey project = change.getProject();
+    Branch.NameKey dest = change.getDest();
+    try (Repository git = gitManager.openRepository(project);
+        ObjectInserter oi = git.newObjectInserter();
+        RevWalk rw = new RevWalk(oi.newReader())) {
+
+      RevCommit sourceCommit =
+          MergeUtil.resolveCommit(git, rw, merge.source);
+      if (!projectControl.canReadCommit(db.get(), git, sourceCommit)) {
+        throw new ResourceNotFoundException(
+            "cannot find source commit: " + merge.source + " to merge.");
+      }
+
+      RevCommit currentPsCommit =
+          rw.parseCommit(ObjectId.fromString(ps.getRevision().get()));
+
+      Timestamp now = TimeUtil.nowTs();
+      IdentifiedUser me = user.get().asIdentifiedUser();
+      PersonIdent author = me.newCommitterIdent(now, serverTimeZone);
+
+      RevCommit newCommit =
+          createMergeCommit(in, projectControl, dest, git, oi, rw,
+              currentPsCommit, sourceCommit, author,
+              ObjectId.fromString(change.getKey().get().substring(1)));
+
+      PatchSet.Id nextPsId = ChangeUtil.nextPatchSetId(ps.getId());
+      PatchSetInserter psInserter =
+          patchSetInserterFactory.create(ctl, nextPsId, newCommit);
+      try (BatchUpdate bu = batchUpdateFactory
+          .create(db.get(), project, me, now)) {
+        bu.setRepository(git, rw, oi);
+        bu.addOp(ctl.getId(), psInserter
+            .setMessage("Uploaded patch set " + nextPsId.get() + ".")
+            .setDraft(ps.isDraft())
+            .setNotify(NotifyHandling.NONE));
+        bu.execute();
+      }
+
+      ChangeJson json =
+          jsonFactory.create(EnumSet.of(ListChangesOption.CURRENT_REVISION));
+      return Response.ok(json.format(psInserter.getChange()));
+    }
+  }
+
+  private RevCommit createMergeCommit(MergePatchSetInput in,
+      ProjectControl projectControl, Branch.NameKey dest, Repository git,
+      ObjectInserter oi, RevWalk rw, RevCommit currentPsCommit,
+      RevCommit sourceCommit, PersonIdent author, ObjectId changeId)
+      throws ResourceNotFoundException, MergeIdenticalTreeException,
+      MergeConflictException, IOException {
+
+    ObjectId parentCommit;
+    if (in.inheritParent) {
+      // inherit first parent from previous patch set
+      parentCommit = currentPsCommit.getParent(0);
+    } else {
+      // get the current branch tip of destination branch
+      Ref destRef = git.getRefDatabase().exactRef(dest.get());
+      if (destRef != null) {
+        parentCommit = destRef.getObjectId();
+      } else {
+        throw new ResourceNotFoundException("cannot find destination branch");
+      }
+    }
+    RevCommit mergeTip = rw.parseCommit(parentCommit);
+
+    String commitMsg;
+    if (Strings.emptyToNull(in.subject) != null) {
+      commitMsg = ChangeIdUtil.insertId(in.subject, changeId);
+    } else {
+      // reuse previous patch set commit message
+      commitMsg = currentPsCommit.getFullMessage();
+    }
+
+    String mergeStrategy = MoreObjects.firstNonNull(
+        Strings.emptyToNull(in.merge.strategy),
+        mergeUtilFactory.create(projectControl.getProjectState())
+            .mergeStrategyName());
+
+    return MergeUtil.createMergeCommit(git, oi, mergeTip, sourceCommit,
+        mergeStrategy, author, commitMsg, rw);
+  }
+}

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

@@ -53,6 +53,7 @@ public class Module extends RestApiModule {
     DynamicMap.mapOf(binder(), VOTE_KIND);
 
     get(CHANGE_KIND).to(GetChange.class);
+    post(CHANGE_KIND, "merge").to(CreateMergePatchSet.class);
     get(CHANGE_KIND, "detail").to(GetDetail.class);
     get(CHANGE_KIND, "topic").to(GetTopic.class);
     get(CHANGE_KIND, "in").to(IncludedIn.class);