Support cherry picking a commit without specific change

The current cherry pick REST endpoint only allows cherry picking a
revision.  This change allows cherry picking a commit which may not be
associated with a change.

Change-Id: Ic6b178dfe267e0e5cc9333470ba792de3c8111d7

Documentation/rest-api-projects.txt

@@ -2060,6 +2060,60 @@ The content is returned as base64 encoded string.
   Ly8gQ29weXJpZ2h0IChDKSAyMDEwIFRoZSBBbmRyb2lkIE9wZW4gU291cmNlIFByb2plY...
 ----
 
+
+[[cherry-pick-commit]]
+=== Cherry Pick Commit
+--
+'POST /projects/link:#project-name[\{project-name\}]/commits/link:#commit-id[\{commit-id\}]/cherrypick'
+--
+
+Cherry-picks a commit of a project to a destination branch.
+
+The destination branch must be provided in the request body inside a
+link:rest-api-changes.html#cherrypick-input[CherryPickInput] entity.
+If the commit message is not set, the commit message of the source
+commit will be used.
+
+.Request
+----
+  POST /projects/work%2Fmy-project/commits/a8a477efffbbf3b44169bb9a1d3a334cbbd9aa96/cherrypick HTTP/1.0
+  Content-Type: application/json; charset=UTF-8
+
+  {
+    "message" : "Implementing Feature X",
+    "destination" : "release-branch"
+  }
+----
+
+As response a link:rest-api-changes.html#change-info[ChangeInfo] entity is returned that
+describes the resulting cherry-picked change.
+
+.Response
+----
+  HTTP/1.1 200 OK
+  Content-Disposition: attachment
+  Content-Type: application/json; charset=UTF-8
+
+  )]}'
+  {
+    "id": "myProject~master~I8473b95934b5732ac55d26311a706c9c2bde9941",
+    "project": "myProject",
+    "branch": "release-branch",
+    "change_id": "I8473b95934b5732ac55d26311a706c9c2bde9941",
+    "subject": "Implementing Feature X",
+    "status": "NEW",
+    "created": "2013-02-01 09:59:32.126000000",
+    "updated": "2013-02-21 11:16:36.775000000",
+    "mergeable": true,
+    "insertions": 12,
+    "deletions": 11,
+    "_number": 3965,
+    "owner": {
+      "name": "John Doe"
+    }
+  }
+----
+
 [[dashboard-endpoints]]
 == Dashboard Endpoints
 

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

@@ -23,6 +23,7 @@ import static org.eclipse.jgit.lib.Constants.SIGNED_OFF_BY_TAG;
 import com.google.common.base.Strings;
 import com.google.common.collect.Iterables;
 import com.google.gerrit.acceptance.AbstractDaemonTest;
+import com.google.gerrit.acceptance.GitUtil;
 import com.google.gerrit.acceptance.PushOneCommit;
 import com.google.gerrit.acceptance.PushOneCommit.Result;
 import com.google.gerrit.acceptance.RestResponse;
@@ -30,11 +31,15 @@ import com.google.gerrit.extensions.api.changes.ChangeApi;
 import com.google.gerrit.extensions.api.changes.CherryPickInput;
 import com.google.gerrit.extensions.api.changes.NotifyHandling;
 import com.google.gerrit.extensions.api.changes.ReviewInput;
+import com.google.gerrit.extensions.api.projects.BranchInput;
 import com.google.gerrit.extensions.client.ChangeStatus;
 import com.google.gerrit.extensions.client.GeneralPreferencesInfo;
 import com.google.gerrit.extensions.common.ChangeInfo;
 import com.google.gerrit.extensions.common.ChangeInput;
+import com.google.gerrit.extensions.common.ChangeMessageInfo;
+import com.google.gerrit.extensions.common.CommitInfo;
 import com.google.gerrit.extensions.common.MergeInput;
+import com.google.gerrit.extensions.common.RevisionInfo;
 import com.google.gerrit.extensions.restapi.BadRequestException;
 import com.google.gerrit.extensions.restapi.MethodNotAllowedException;
 import com.google.gerrit.extensions.restapi.RestApiException;
@@ -45,10 +50,13 @@ import com.google.gerrit.server.git.ChangeAlreadyMergedException;
 import com.google.gerrit.testutil.ConfigSuite;
 import com.google.gerrit.testutil.FakeEmailSender.Message;
 import com.google.gerrit.testutil.TestTimeUtil;
+import java.util.Iterator;
 import java.util.List;
+import org.eclipse.jgit.junit.TestRepository;
 import org.eclipse.jgit.lib.Config;
 import org.eclipse.jgit.lib.ObjectId;
 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;
@@ -278,6 +286,79 @@ public class CreateChangeIT extends AbstractDaemonTest {
     assertCreateSucceeds(in);
   }
 
+  @Test
+  public void cherryPickCommitWithoutChangeId() throws Exception {
+    // This test is a little superfluous, since the current cherry-pick code ignores
+    // the commit message of the to-be-cherry-picked change, using the one in
+    // CherryPickInput instead.
+    CherryPickInput input = new CherryPickInput();
+    input.destination = "foo";
+    input.message = "it goes to foo branch";
+    gApi.projects().name(project.get()).branch(input.destination).create(new BranchInput());
+
+    RevCommit revCommit = createNewCommitWithoutChangeId();
+    ChangeInfo changeInfo =
+        gApi.projects().name(project.get()).commit(revCommit.getName()).cherryPick(input).get();
+
+    assertThat(changeInfo.messages).hasSize(1);
+    Iterator<ChangeMessageInfo> messageIterator = changeInfo.messages.iterator();
+    String expectedMessage =
+        String.format("Patch Set 1: Cherry Picked from commit %s.", revCommit.getName());
+    assertThat(messageIterator.next().message).isEqualTo(expectedMessage);
+
+    RevisionInfo revInfo = changeInfo.revisions.get(changeInfo.currentRevision);
+    assertThat(revInfo).isNotNull();
+    CommitInfo commitInfo = revInfo.commit;
+    assertThat(commitInfo.message)
+        .isEqualTo(input.message + "\n\nChange-Id: " + changeInfo.changeId + "\n");
+  }
+
+  @Test
+  public void cherryPickCommitWithChangeId() throws Exception {
+    CherryPickInput input = new CherryPickInput();
+    input.destination = "foo";
+
+    RevCommit revCommit = createChange().getCommit();
+    List<String> footers = revCommit.getFooterLines("Change-Id");
+    assertThat(footers).hasSize(1);
+    String changeId = footers.get(0);
+
+    input.message = "it goes to foo branch\n\nChange-Id: " + changeId;
+    gApi.projects().name(project.get()).branch(input.destination).create(new BranchInput());
+
+    ChangeInfo changeInfo =
+        gApi.projects().name(project.get()).commit(revCommit.getName()).cherryPick(input).get();
+
+    assertThat(changeInfo.messages).hasSize(1);
+    Iterator<ChangeMessageInfo> messageIterator = changeInfo.messages.iterator();
+    String expectedMessage =
+        String.format("Patch Set 1: Cherry Picked from commit %s.", revCommit.getName());
+    assertThat(messageIterator.next().message).isEqualTo(expectedMessage);
+
+    RevisionInfo revInfo = changeInfo.revisions.get(changeInfo.currentRevision);
+    assertThat(revInfo).isNotNull();
+    assertThat(revInfo.commit.message).isEqualTo(input.message + "\n");
+  }
+
+  private RevCommit createNewCommitWithoutChangeId() throws Exception {
+    try (Repository repo = repoManager.openRepository(project);
+        RevWalk walk = new RevWalk(repo)) {
+      Ref ref = repo.exactRef("refs/heads/master");
+      RevCommit tip = null;
+      if (ref != null) {
+        tip = walk.parseCommit(ref.getObjectId());
+      }
+      TestRepository<?> testSrcRepo = new TestRepository<>(repo);
+      TestRepository<?>.BranchBuilder builder = testSrcRepo.branch("refs/heads/master");
+      RevCommit revCommit =
+          tip == null
+              ? builder.commit().message("commit 1").add("a.txt", "content").create()
+              : builder.commit().parent(tip).message("commit 1").add("a.txt", "content").create();
+      assertThat(GitUtil.getChangeId(testSrcRepo, revCommit).isPresent()).isFalse();
+      return revCommit;
+    }
+  }
+
   private ChangeInput newChangeInput(ChangeStatus status) {
     ChangeInput in = new ChangeInput();
     in.project = project.get();

gerrit-extension-api/src/main/java/com/google/gerrit/extensions/api/projects/CommitApi.java

@@ -0,0 +1,33 @@
+// Copyright (C) 2017 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.extensions.api.projects;
+
+import com.google.gerrit.extensions.api.changes.ChangeApi;
+import com.google.gerrit.extensions.api.changes.CherryPickInput;
+import com.google.gerrit.extensions.restapi.NotImplementedException;
+import com.google.gerrit.extensions.restapi.RestApiException;
+
+public interface CommitApi {
+
+  ChangeApi cherryPick(CherryPickInput input) throws RestApiException;
+
+  /** A default implementation for source compatibility when adding new methods to the interface. */
+  class NotImplemented implements CommitApi {
+    @Override
+    public ChangeApi cherryPick(CherryPickInput input) {
+      throw new NotImplementedException();
+    }
+  }
+}

gerrit-extension-api/src/main/java/com/google/gerrit/extensions/api/projects/ProjectApi.java

@@ -124,6 +124,14 @@ public interface ProjectApi {
    */
   TagApi tag(String ref) throws RestApiException;
 
+  /**
+   * Lookup a commit by its {@Code ObjectId} string.
+   *
+   * @param commit the {@Code ObjectId} string.
+   * @return API for accessing the commit.
+   */
+  CommitApi commit(String commit) throws RestApiException;
+
   /**
    * A default implementation which allows source compatibility when adding new methods to the
    * interface.
@@ -218,5 +226,10 @@ public interface ProjectApi {
     public void deleteTags(DeleteTagsInput in) {
       throw new NotImplementedException();
     }
+
+    @Override
+    public CommitApi commit(String commit) {
+      throw new NotImplementedException();
+    }
   }
 }

gerrit-server/src/main/java/com/google/gerrit/server/api/projects/CommitApiImpl.java

@@ -0,0 +1,55 @@
+// Copyright (C) 2017 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.api.projects;
+
+import com.google.gerrit.extensions.api.changes.ChangeApi;
+import com.google.gerrit.extensions.api.changes.Changes;
+import com.google.gerrit.extensions.api.changes.CherryPickInput;
+import com.google.gerrit.extensions.api.projects.CommitApi;
+import com.google.gerrit.extensions.restapi.RestApiException;
+import com.google.gerrit.server.change.CherryPickCommit;
+import com.google.gerrit.server.project.CommitResource;
+import com.google.gerrit.server.update.UpdateException;
+import com.google.gwtorm.server.OrmException;
+import com.google.inject.Inject;
+import com.google.inject.assistedinject.Assisted;
+import java.io.IOException;
+
+public class CommitApiImpl implements CommitApi {
+  public interface Factory {
+    CommitApiImpl create(CommitResource r);
+  }
+
+  private final Changes changes;
+  private final CherryPickCommit cherryPickCommit;
+  private final CommitResource commitResource;
+
+  @Inject
+  CommitApiImpl(
+      Changes changes, CherryPickCommit cherryPickCommit, @Assisted CommitResource commitResource) {
+    this.changes = changes;
+    this.cherryPickCommit = cherryPickCommit;
+    this.commitResource = commitResource;
+  }
+
+  @Override
+  public ChangeApi cherryPick(CherryPickInput input) throws RestApiException {
+    try {
+      return changes.id(cherryPickCommit.apply(commitResource, input)._number);
+    } catch (OrmException | IOException | UpdateException e) {
+      throw new RestApiException("Cannot cherry pick", e);
+    }
+  }
+}

gerrit-server/src/main/java/com/google/gerrit/server/api/projects/Module.java

@@ -26,5 +26,6 @@ public class Module extends FactoryModule {
     factory(TagApiImpl.Factory.class);
     factory(ProjectApiImpl.Factory.class);
     factory(ChildProjectApiImpl.Factory.class);
+    factory(CommitApiImpl.Factory.class);
   }
 }

gerrit-server/src/main/java/com/google/gerrit/server/api/projects/ProjectApiImpl.java

@@ -21,6 +21,7 @@ import com.google.gerrit.extensions.api.access.ProjectAccessInput;
 import com.google.gerrit.extensions.api.projects.BranchApi;
 import com.google.gerrit.extensions.api.projects.BranchInfo;
 import com.google.gerrit.extensions.api.projects.ChildProjectApi;
+import com.google.gerrit.extensions.api.projects.CommitApi;
 import com.google.gerrit.extensions.api.projects.ConfigInfo;
 import com.google.gerrit.extensions.api.projects.ConfigInput;
 import com.google.gerrit.extensions.api.projects.DeleteBranchesInput;
@@ -39,6 +40,7 @@ import com.google.gerrit.extensions.restapi.RestApiException;
 import com.google.gerrit.extensions.restapi.TopLevelResource;
 import com.google.gerrit.server.CurrentUser;
 import com.google.gerrit.server.project.ChildProjectsCollection;
+import com.google.gerrit.server.project.CommitsCollection;
 import com.google.gerrit.server.project.CreateProject;
 import com.google.gerrit.server.project.DeleteBranches;
 import com.google.gerrit.server.project.DeleteTags;
@@ -89,6 +91,8 @@ public class ProjectApiImpl implements ProjectApi {
   private final ListTags listTags;
   private final DeleteBranches deleteBranches;
   private final DeleteTags deleteTags;
+  private final CommitsCollection commitsCollection;
+  private final CommitApiImpl.Factory commitApi;
 
   @AssistedInject
   ProjectApiImpl(
@@ -111,6 +115,8 @@ public class ProjectApiImpl implements ProjectApi {
       ListTags listTags,
       DeleteBranches deleteBranches,
       DeleteTags deleteTags,
+      CommitsCollection commitsCollection,
+      CommitApiImpl.Factory commitApi,
       @Assisted ProjectResource project) {
     this(
         user,
@@ -133,6 +139,8 @@ public class ProjectApiImpl implements ProjectApi {
         deleteBranches,
         deleteTags,
         project,
+        commitsCollection,
+        commitApi,
         null);
   }
 
@@ -157,6 +165,8 @@ public class ProjectApiImpl implements ProjectApi {
       ListTags listTags,
       DeleteBranches deleteBranches,
       DeleteTags deleteTags,
+      CommitsCollection commitsCollection,
+      CommitApiImpl.Factory commitApi,
       @Assisted String name) {
     this(
         user,
@@ -179,6 +189,8 @@ public class ProjectApiImpl implements ProjectApi {
         deleteBranches,
         deleteTags,
         null,
+        commitsCollection,
+        commitApi,
         name);
   }
 
@@ -203,6 +215,8 @@ public class ProjectApiImpl implements ProjectApi {
       DeleteBranches deleteBranches,
       DeleteTags deleteTags,
       ProjectResource project,
+      CommitsCollection commitsCollection,
+      CommitApiImpl.Factory commitApi,
       String name) {
     this.user = user;
     this.createProjectFactory = createProjectFactory;
@@ -225,6 +239,8 @@ public class ProjectApiImpl implements ProjectApi {
     this.listTags = listTags;
     this.deleteBranches = deleteBranches;
     this.deleteTags = deleteTags;
+    this.commitsCollection = commitsCollection;
+    this.commitApi = commitApi;
   }
 
   @Override
@@ -393,6 +409,15 @@ public class ProjectApiImpl implements ProjectApi {
     }
   }
 
+  @Override
+  public CommitApi commit(String commit) throws RestApiException {
+    try {
+      return commitApi.create(commitsCollection.parse(checkExists(), IdString.fromDecoded(commit)));
+    } catch (IOException e) {
+      throw new RestApiException("Cannot parse commit", e);
+    }
+  }
+
   private ProjectResource checkExists() throws ResourceNotFoundException {
     if (project == null) {
       throw new ResourceNotFoundException(name);

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

@@ -16,6 +16,7 @@ package com.google.gerrit.server.change;
 
 import com.google.common.base.Strings;
 import com.google.gerrit.common.FooterConstants;
+import com.google.gerrit.common.Nullable;
 import com.google.gerrit.common.TimeUtil;
 import com.google.gerrit.extensions.api.changes.NotifyHandling;
 import com.google.gerrit.extensions.restapi.MergeConflictException;
@@ -42,7 +43,6 @@ import com.google.gerrit.server.git.MergeUtil;
 import com.google.gerrit.server.git.validators.CommitValidators;
 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.ProjectState;
 import com.google.gerrit.server.project.RefControl;
 import com.google.gerrit.server.query.change.ChangeData;
@@ -59,9 +59,6 @@ import java.io.IOException;
 import java.sql.Timestamp;
 import java.util.List;
 import java.util.TimeZone;
-import org.eclipse.jgit.errors.IncorrectObjectTypeException;
-import org.eclipse.jgit.errors.MissingObjectException;
-import org.eclipse.jgit.errors.RepositoryNotFoundException;
 import org.eclipse.jgit.lib.ObjectId;
 import org.eclipse.jgit.lib.ObjectInserter;
 import org.eclipse.jgit.lib.PersonIdent;
@@ -114,23 +111,42 @@ public class CherryPickChange {
   }
 
   public Change.Id cherryPick(
-      Change change,
-      PatchSet patch,
-      final String message,
-      final String ref,
-      final RefControl refControl,
-      int parent)
-      throws NoSuchChangeException, OrmException, MissingObjectException,
-          IncorrectObjectTypeException, IOException, InvalidChangeOperationException,
-          IntegrationException, UpdateException, RestApiException {
+      Change change, PatchSet patch, String message, String ref, RefControl refControl, int parent)
+      throws OrmException, IOException, InvalidChangeOperationException, IntegrationException,
+          UpdateException, RestApiException {
+    return cherryPick(
+        change.getId(),
+        patch.getId(),
+        change.getDest(),
+        change.getTopic(),
+        change.getProject(),
+        ObjectId.fromString(patch.getRevision().get()),
+        message,
+        ref,
+        refControl,
+        parent);
+  }
 
-    if (Strings.isNullOrEmpty(ref)) {
+  public Change.Id cherryPick(
+      @Nullable Change.Id sourceChangeId,
+      @Nullable PatchSet.Id sourcePatchId,
+      @Nullable Branch.NameKey sourceBranch,
+      @Nullable String sourceChangeTopic,
+      Project.NameKey project,
+      ObjectId sourceCommit,
+      String message,
+      String targetRef,
+      RefControl targetRefControl,
+      int parent)
+      throws OrmException, IOException, InvalidChangeOperationException, IntegrationException,
+          UpdateException, RestApiException {
+
+    if (Strings.isNullOrEmpty(targetRef)) {
       throw new InvalidChangeOperationException(
           "Cherry Pick: Destination branch cannot be null or empty");
     }
 
-    Project.NameKey project = change.getProject();
-    String destinationBranch = RefNames.shortName(ref);
+    String destinationBranch = RefNames.shortName(targetRef);
     IdentifiedUser identifiedUser = user.get();
     try (Repository git = gitManager.openRepository(project);
         // This inserter and revwalk *must* be passed to any BatchUpdates
@@ -138,7 +154,7 @@ public class CherryPickChange {
         // before patch sets are updated.
         ObjectInserter oi = git.newObjectInserter();
         CodeReviewRevWalk revWalk = CodeReviewCommit.newRevWalk(oi.newReader())) {
-      Ref destRef = git.getRefDatabase().exactRef(ref);
+      Ref destRef = git.getRefDatabase().exactRef(targetRef);
       if (destRef == null) {
         throw new InvalidChangeOperationException(
             String.format("Branch %s does not exist.", destinationBranch));
@@ -146,8 +162,7 @@ public class CherryPickChange {
 
       CodeReviewCommit mergeTip = revWalk.parseCommit(destRef.getObjectId());
 
-      CodeReviewCommit commitToCherryPick =
-          revWalk.parseCommit(ObjectId.fromString(patch.getRevision().get()));
+      CodeReviewCommit commitToCherryPick = revWalk.parseCommit(sourceCommit);
 
       if (parent <= 0 || parent > commitToCherryPick.getParentCount()) {
         throw new InvalidChangeOperationException(
@@ -171,7 +186,7 @@ public class CherryPickChange {
 
       CodeReviewCommit cherryPickCommit;
       try {
-        ProjectState projectState = refControl.getProjectControl().getProjectState();
+        ProjectState projectState = targetRefControl.getProjectControl().getProjectState();
         cherryPickCommit =
             mergeUtilFactory
                 .create(projectState)
@@ -195,7 +210,7 @@ public class CherryPickChange {
           changeKey = new Change.Key("I" + computedChangeId.name());
         }
 
-        Branch.NameKey newDest = new Branch.NameKey(change.getProject(), destRef.getName());
+        Branch.NameKey newDest = new Branch.NameKey(project, destRef.getName());
         List<ChangeData> destChanges =
             queryProvider.get().setLimit(2).byBranchKey(newDest, changeKey);
         if (destChanges.size() > 1) {
@@ -205,32 +220,37 @@ public class CherryPickChange {
                   + " reside on the same branch. "
                   + "Cannot create a new patch set.");
         }
-        try (BatchUpdate bu =
-            batchUpdateFactory.create(
-                db.get(), change.getDest().getParentKey(), identifiedUser, now)) {
+        try (BatchUpdate bu = batchUpdateFactory.create(db.get(), project, identifiedUser, now)) {
           bu.setRepository(git, revWalk, oi);
           Change.Id result;
           if (destChanges.size() == 1) {
             // The change key exists on the destination branch. The cherry pick
             // will be added as a new patch set.
             ChangeControl destCtl =
-                refControl.getProjectControl().controlFor(destChanges.get(0).notes());
+                targetRefControl.getProjectControl().controlFor(destChanges.get(0).notes());
             result = insertPatchSet(bu, git, destCtl, cherryPickCommit);
           } else {
             // Change key not found on destination branch. We can create a new
             // change.
             String newTopic = null;
-            if (!Strings.isNullOrEmpty(change.getTopic())) {
-              newTopic = change.getTopic() + "-" + newDest.getShortName();
+            if (!Strings.isNullOrEmpty(sourceChangeTopic)) {
+              newTopic = sourceChangeTopic + "-" + newDest.getShortName();
             }
             result =
                 createNewChange(
-                    bu, cherryPickCommit, refControl.getRefName(), newTopic, change.getDest());
+                    bu,
+                    cherryPickCommit,
+                    targetRefControl.getRefName(),
+                    newTopic,
+                    sourceBranch,
+                    sourceCommit);
 
-            bu.addOp(
-                change.getId(),
-                new AddMessageToSourceChangeOp(
-                    changeMessagesUtil, patch.getId(), destinationBranch, cherryPickCommit));
+            if (sourceChangeId != null && sourcePatchId != null) {
+              bu.addOp(
+                  sourceChangeId,
+                  new AddMessageToSourceChangeOp(
+                      changeMessagesUtil, sourcePatchId, destinationBranch, cherryPickCommit));
+            }
           }
           bu.execute();
           return result;
@@ -238,8 +258,6 @@ public class CherryPickChange {
       } catch (MergeIdenticalTreeException | MergeConflictException e) {
         throw new IntegrationException("Cherry pick failed: " + e.getMessage());
       }
-    } catch (RepositoryNotFoundException e) {
-      throw new NoSuchChangeException(change.getId(), e);
     }
   }
 
@@ -266,7 +284,8 @@ public class CherryPickChange {
       CodeReviewCommit cherryPickCommit,
       String refName,
       String topic,
-      Branch.NameKey sourceBranch)
+      Branch.NameKey sourceBranch,
+      ObjectId sourceCommit)
       throws OrmException {
     Change.Id changeId = new Change.Id(seq.nextChangeId());
     ChangeInserter ins =
@@ -275,7 +294,7 @@ public class CherryPickChange {
             .setValidatePolicy(CommitValidators.Policy.GERRIT)
             .setTopic(topic);
 
-    ins.setMessage(messageForDestinationChange(ins.getPatchSetId(), sourceBranch));
+    ins.setMessage(messageForDestinationChange(ins.getPatchSetId(), sourceBranch, sourceCommit));
     bu.insertChange(ins);
     return changeId;
   }
@@ -317,12 +336,16 @@ public class CherryPickChange {
     }
   }
 
-  private String messageForDestinationChange(PatchSet.Id patchSetId, Branch.NameKey sourceBranch) {
-    return new StringBuilder("Patch Set ")
-        .append(patchSetId.get())
-        .append(": Cherry Picked from branch ")
-        .append(sourceBranch.getShortName())
-        .append(".")
-        .toString();
+  private String messageForDestinationChange(
+      PatchSet.Id patchSetId, Branch.NameKey sourceBranch, ObjectId sourceCommit) {
+    StringBuilder stringBuilder = new StringBuilder("Patch Set ").append(patchSetId.get());
+
+    if (sourceBranch != null) {
+      stringBuilder.append(": Cherry Picked from branch ").append(sourceBranch.getShortName());
+    } else {
+      stringBuilder.append(": Cherry Picked from commit ").append(sourceCommit.getName());
+    }
+
+    return stringBuilder.append(".").toString();
   }
 }

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

@@ -0,0 +1,98 @@
+// Copyright (C) 2017 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.Strings;
+import com.google.gerrit.common.data.Capable;
+import com.google.gerrit.extensions.api.changes.CherryPickInput;
+import com.google.gerrit.extensions.common.ChangeInfo;
+import com.google.gerrit.extensions.restapi.AuthException;
+import com.google.gerrit.extensions.restapi.BadRequestException;
+import com.google.gerrit.extensions.restapi.ResourceConflictException;
+import com.google.gerrit.extensions.restapi.RestApiException;
+import com.google.gerrit.extensions.restapi.RestModifyView;
+import com.google.gerrit.reviewdb.client.Change;
+import com.google.gerrit.reviewdb.client.Project;
+import com.google.gerrit.reviewdb.client.RefNames;
+import com.google.gerrit.server.git.IntegrationException;
+import com.google.gerrit.server.project.CommitResource;
+import com.google.gerrit.server.project.InvalidChangeOperationException;
+import com.google.gerrit.server.project.ProjectControl;
+import com.google.gerrit.server.project.RefControl;
+import com.google.gerrit.server.update.UpdateException;
+import com.google.gwtorm.server.OrmException;
+import com.google.inject.Inject;
+import com.google.inject.Singleton;
+import java.io.IOException;
+import org.eclipse.jgit.revwalk.RevCommit;
+
+@Singleton
+public class CherryPickCommit implements RestModifyView<CommitResource, CherryPickInput> {
+
+  private final CherryPickChange cherryPickChange;
+  private final ChangeJson.Factory json;
+
+  @Inject
+  CherryPickCommit(CherryPickChange cherryPickChange, ChangeJson.Factory json) {
+    this.cherryPickChange = cherryPickChange;
+    this.json = json;
+  }
+
+  @Override
+  public ChangeInfo apply(CommitResource rsrc, CherryPickInput input)
+      throws OrmException, IOException, UpdateException, RestApiException {
+    String message = Strings.nullToEmpty(input.message).trim();
+    String destination = Strings.nullToEmpty(input.destination).trim();
+    int parent = input.parent == null ? 1 : input.parent;
+
+    if (destination.isEmpty()) {
+      throw new BadRequestException("destination must be non-empty");
+    }
+
+    ProjectControl projectControl = rsrc.getProject();
+    Capable capable = projectControl.canPushToAtLeastOneRef();
+    if (capable != Capable.OK) {
+      throw new AuthException(capable.getMessage());
+    }
+
+    RevCommit commit = rsrc.getCommit();
+    String refName = RefNames.fullName(destination);
+    RefControl refControl = projectControl.controlForRef(refName);
+    if (!refControl.canUpload()) {
+      throw new AuthException("Not allowed to cherry pick " + commit + " to " + destination);
+    }
+
+    Project.NameKey project = projectControl.getProject().getNameKey();
+    try {
+      Change.Id cherryPickedChangeId =
+          cherryPickChange.cherryPick(
+              null,
+              null,
+              null,
+              null,
+              project,
+              commit,
+              message.isEmpty() ? commit.getFullMessage() : message,
+              refName,
+              refControl,
+              parent);
+      return json.noOptions().format(project, cherryPickedChangeId);
+    } catch (InvalidChangeOperationException e) {
+      throw new BadRequestException(e.getMessage());
+    } catch (IntegrationException e) {
+      throw new ResourceConflictException(e.getMessage());
+    }
+  }
+}

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

@@ -24,6 +24,7 @@ import static com.google.gerrit.server.project.TagResource.TAG_KIND;
 
 import com.google.gerrit.extensions.registration.DynamicMap;
 import com.google.gerrit.extensions.restapi.RestApiModule;
+import com.google.gerrit.server.change.CherryPickCommit;
 
 public class Module extends RestApiModule {
   @Override
@@ -96,6 +97,8 @@ public class Module extends RestApiModule {
     get(PROJECT_KIND, "config").to(GetConfig.class);
     put(PROJECT_KIND, "config").to(PutConfig.class);
 
+    post(COMMIT_KIND, "cherrypick").to(CherryPickCommit.class);
+
     factory(DeleteRef.Factory.class);
   }
 }