From 0d99067b8ddae3554c1e067d5a9cc2fc6d8c8629 Mon Sep 17 00:00:00 2001
From: Zalan Blenessy <zalanb@axis.com>
Date: Fri, 20 Mar 2015 17:31:54 +0100
Subject: [PATCH] Improve rebase usability with the RebaseDialog

Since [1] the Rebase button is always visible for the current patch
set. This leads to somewhat degraded usability, since its no longer
obvious whether a change can be rebased or the change is up-to-date
and consequently any rebase attempts will fail.

This patch solves the problem by:
1. Displaying an orange circle next to the 'Parent(s)' text when the
   parent commit is not current, meaning the parent branch or change
   has moved on.
2. The Rebase (send) button in the RebaseDialog will be disabled, if
   the change is up-to-date and the "Change parent revision"
   checkbox is disabled (default).

[1] https://gerrit-review.googlesource.com/#/c/63196/

Change-Id: Iaa1b0ce4cf3309330a55d1ab48d5422536089667
---
 .../google/gerrit/client/change/Actions.java  | 15 ++++++++-
 .../gerrit/client/change/CommitBox.java       | 16 ++++++++++
 .../gerrit/client/change/CommitBox.ui.xml     | 22 +++++++++++--
 .../gerrit/client/change/RebaseAction.java    |  4 +--
 .../client/changes/ChangeConstants.java       |  1 +
 .../client/changes/ChangeConstants.properties |  1 +
 .../google/gerrit/client/ui/RebaseDialog.java | 32 +++++++++++++++----
 .../gerrit/server/change/ActionJson.java      |  8 +++--
 .../gerrit/server/change/ChangeJson.java      |  8 +++--
 .../gerrit/server/change/ChangeResource.java  |  9 ++++--
 .../server/change/ChangesCollection.java      | 10 ++++--
 .../google/gerrit/server/change/Rebase.java   |  8 ++++-
 .../server/changedetail/RebaseChange.java     | 19 +++++++++--
 .../gerrit/server/change/CommentsTest.java    |  4 +--
 14 files changed, 130 insertions(+), 27 deletions(-)

diff --git a/gerrit-gwtui/src/main/java/com/google/gerrit/client/change/Actions.java b/gerrit-gwtui/src/main/java/com/google/gerrit/client/change/Actions.java
index 525684d44d..edf11058e3 100644
--- a/gerrit-gwtui/src/main/java/com/google/gerrit/client/change/Actions.java
+++ b/gerrit-gwtui/src/main/java/com/google/gerrit/client/change/Actions.java
@@ -128,6 +128,10 @@ class Actions extends Composite {
       }
       a2b(actions, "cherrypick", cherrypick);
       a2b(actions, "rebase", rebase);
+      if (rebase.isVisible()) {
+        // it is the rebase button in RebaseDialog that the server wants to disable
+        rebase.setEnabled(true);
+      }
       for (String id : filterNonCore(actions)) {
         add(new ActionButton(info, revInfo, actions.get(id)));
       }
@@ -177,7 +181,16 @@ class Actions extends Composite {
 
   @UiHandler("rebase")
   void onRebase(@SuppressWarnings("unused") ClickEvent e) {
-    RebaseAction.call(rebase, project, changeInfo.branch(), changeId, revision);
+    boolean enabled = true;
+    RevisionInfo revInfo = changeInfo.revision(revision);
+    if (revInfo.has_actions()) {
+        NativeMap<ActionInfo> actions = revInfo.actions();
+        if (actions.containsKey("rebase")) {
+          enabled = actions.get("rebase").enabled();
+        }
+    }
+    RebaseAction.call(rebase, project, changeInfo.branch(), changeId, revision,
+        enabled);
   }
 
   @UiHandler("submit")
diff --git a/gerrit-gwtui/src/main/java/com/google/gerrit/client/change/CommitBox.java b/gerrit-gwtui/src/main/java/com/google/gerrit/client/change/CommitBox.java
index 4bdd17fc03..93db1a7afe 100644
--- a/gerrit-gwtui/src/main/java/com/google/gerrit/client/change/CommitBox.java
+++ b/gerrit-gwtui/src/main/java/com/google/gerrit/client/change/CommitBox.java
@@ -19,11 +19,13 @@ import com.google.gerrit.client.FormatUtil;
 import com.google.gerrit.client.Gerrit;
 import com.google.gerrit.client.GitwebLink;
 import com.google.gerrit.client.WebLinkInfo;
+import com.google.gerrit.client.actions.ActionInfo;
 import com.google.gerrit.client.account.AccountInfo;
 import com.google.gerrit.client.changes.ChangeInfo;
 import com.google.gerrit.client.changes.ChangeInfo.CommitInfo;
 import com.google.gerrit.client.changes.ChangeInfo.GitPerson;
 import com.google.gerrit.client.changes.ChangeInfo.RevisionInfo;
+import com.google.gerrit.client.rpc.NativeMap;
 import com.google.gerrit.client.rpc.Natives;
 import com.google.gerrit.client.ui.CommentLinkProcessor;
 import com.google.gerrit.client.ui.InlineHyperlink;
@@ -46,6 +48,7 @@ import com.google.gwt.user.client.ui.HTML;
 import com.google.gwt.user.client.ui.HTMLPanel;
 import com.google.gwt.user.client.ui.Image;
 import com.google.gwt.user.client.ui.ScrollPanel;
+import com.google.gwt.user.client.ui.UIObject;
 import com.google.gwtexpui.clippy.client.CopyableLabel;
 import com.google.gwtexpui.safehtml.client.SafeHtmlBuilder;
 
@@ -77,6 +80,7 @@ class CommitBox extends Composite {
   @UiField HTML text;
   @UiField ScrollPanel scroll;
   @UiField Button more;
+  @UiField Element parentNotCurrentText;
   private boolean expanded;
 
   CommitBox() {
@@ -121,7 +125,19 @@ class CommitBox extends Composite {
     if (revInfo.commit().parents().length() > 1) {
       mergeCommit.setVisible(true);
     }
+
     setParents(change.project(), revInfo.commit().parents());
+
+    // display the orange ball if parent has moved on (not current)
+    boolean parentNotCurrent = false;
+    if (revInfo.has_actions()) {
+      NativeMap<ActionInfo> actions = revInfo.actions();
+      if (actions.containsKey("rebase")) {
+        parentNotCurrent = actions.get("rebase").enabled();
+      }
+    }
+    UIObject.setVisible(parentNotCurrentText, parentNotCurrent);
+    parentNotCurrentText.setInnerText(parentNotCurrent ? "\u25CF" : "");
   }
 
   private void setWebLinks(ChangeInfo change, String revision,
diff --git a/gerrit-gwtui/src/main/java/com/google/gerrit/client/change/CommitBox.ui.xml b/gerrit-gwtui/src/main/java/com/google/gerrit/client/change/CommitBox.ui.xml
index 5b7fb89b06..93312fa874 100644
--- a/gerrit-gwtui/src/main/java/com/google/gerrit/client/change/CommitBox.ui.xml
+++ b/gerrit-gwtui/src/main/java/com/google/gerrit/client/change/CommitBox.ui.xml
@@ -68,7 +68,7 @@ limitations under the License.
       padding: 0;
       width: 560px;
     }
-    .header th { width: 70px; }
+    .header th { width: 72px; }
     .header td { white-space: nowrap; }
     .date { width: 132px; }
 
@@ -106,6 +106,16 @@ limitations under the License.
       height: 16px !important;
       vertical-align: bottom;
     }
+
+    .parent {
+      margin-right: 3px;
+      float: left;
+    }
+    .parentNotCurrent {
+      color: #FFA62F;   <!-- orange -->
+      font-weight: bold;
+    }
+
   </ui:style>
   <g:HTMLPanel>
     <g:ScrollPanel styleName='{style.scroll}' ui:field='scroll'>
@@ -163,7 +173,15 @@ limitations under the License.
         </td>
       </tr>
       <tr ui:field='firstParent' style='display: none'>
-        <th><ui:msg>Parent(s)</ui:msg></th>
+        <th>
+          <div class='{style.parent}'>
+            <ui:msg>Parent(s)</ui:msg>
+          </div>
+          <div ui:field='parentNotCurrentText'
+              title='Not current - rebase possible'
+              class='{style.parentNotCurrent}'
+              style='display: none' aria-hidden='true'/>
+        </th>
         <td>
           <g:FlowPanel ui:field='parentCommits'/>
         </td>
diff --git a/gerrit-gwtui/src/main/java/com/google/gerrit/client/change/RebaseAction.java b/gerrit-gwtui/src/main/java/com/google/gerrit/client/change/RebaseAction.java
index ffe96279ad..790198b014 100644
--- a/gerrit-gwtui/src/main/java/com/google/gerrit/client/change/RebaseAction.java
+++ b/gerrit-gwtui/src/main/java/com/google/gerrit/client/change/RebaseAction.java
@@ -27,10 +27,10 @@ import com.google.gwt.user.client.ui.PopupPanel;
 
 class RebaseAction {
   static void call(final Button b, final String project, final String branch,
-      final Change.Id id, final String revision) {
+      final Change.Id id, final String revision, final boolean enabled) {
     b.setEnabled(false);
 
-    new RebaseDialog(project, branch, id) {
+    new RebaseDialog(project, branch, id, enabled) {
       @Override
       public void onSend() {
         ChangeApi.rebase(id.get(), revision, getBase(), new GerritCallback<ChangeInfo>() {
diff --git a/gerrit-gwtui/src/main/java/com/google/gerrit/client/changes/ChangeConstants.java b/gerrit-gwtui/src/main/java/com/google/gerrit/client/changes/ChangeConstants.java
index 00c4404a39..6531129f09 100644
--- a/gerrit-gwtui/src/main/java/com/google/gerrit/client/changes/ChangeConstants.java
+++ b/gerrit-gwtui/src/main/java/com/google/gerrit/client/changes/ChangeConstants.java
@@ -166,6 +166,7 @@ public interface ChangeConstants extends Constants {
 
   String buttonRebaseChangeSend();
   String rebaseConfirmMessage();
+  String rebaseNotPossibleMessage();
   String rebasePlaceholderMessage();
   String rebaseTitle();
 
diff --git a/gerrit-gwtui/src/main/java/com/google/gerrit/client/changes/ChangeConstants.properties b/gerrit-gwtui/src/main/java/com/google/gerrit/client/changes/ChangeConstants.properties
index 9bf3f39c80..45415c5629 100644
--- a/gerrit-gwtui/src/main/java/com/google/gerrit/client/changes/ChangeConstants.properties
+++ b/gerrit-gwtui/src/main/java/com/google/gerrit/client/changes/ChangeConstants.properties
@@ -152,6 +152,7 @@ cherryPickTitle = Code Review - Cherry Pick Change to Another Branch
 
 buttonRebaseChangeSend = Rebase
 rebaseConfirmMessage = Change parent revision
+rebaseNotPossibleMessage = Change is already up to date
 rebasePlaceholderMessage = (subject, change number, or leave empty)
 rebaseTitle = Code Review - Rebase Change
 
diff --git a/gerrit-gwtui/src/main/java/com/google/gerrit/client/ui/RebaseDialog.java b/gerrit-gwtui/src/main/java/com/google/gerrit/client/ui/RebaseDialog.java
index 6b96604585..5f47d981e5 100644
--- a/gerrit-gwtui/src/main/java/com/google/gerrit/client/ui/RebaseDialog.java
+++ b/gerrit-gwtui/src/main/java/com/google/gerrit/client/ui/RebaseDialog.java
@@ -36,10 +36,12 @@ public abstract class RebaseDialog extends CommentedActionDialog {
   private final SuggestBox base;
   private final CheckBox cb;
   private List<ChangeInfo> changes;
+  private final boolean sendEnabled;
 
   public RebaseDialog(final String project, final String branch,
-      final Change.Id changeId) {
+      final Change.Id changeId, final boolean sendEnabled) {
     super(Util.C.rebaseTitle(), null);
+    this.sendEnabled = sendEnabled;
     sendButton.setText(Util.C.buttonRebaseChangeSend());
 
     // create the suggestion box
@@ -63,7 +65,6 @@ public abstract class RebaseDialog extends CommentedActionDialog {
         done.onSuggestionsReady(request, new Response(suggestions));
       }
     });
-    base.setEnabled(false);
     base.getElement().setAttribute("placeholder",
         Util.C.rebasePlaceholderMessage());
     base.setStyleName(Gerrit.RESOURCES.css().rebaseSuggestBox());
@@ -81,13 +82,11 @@ public abstract class RebaseDialog extends CommentedActionDialog {
                 @Override
                 public void onSuccess(ChangeList result) {
                   changes = Natives.asList(result);
-                  base.setEnabled(true);
-                  base.setFocus(true);
+                  updateControls(true);
                 }
               });
         } else {
-          base.setEnabled(false);
-          sendButton.setFocus(true);
+          updateControls(false);
         }
       }
     });
@@ -102,7 +101,26 @@ public abstract class RebaseDialog extends CommentedActionDialog {
   public void center() {
     super.center();
     GlobalKey.dialog(this);
-    sendButton.setFocus(true);
+    updateControls(false);
+  }
+
+  private void updateControls(boolean changeParentEnabled) {
+    if (changeParentEnabled) {
+      sendButton.setTitle(null);
+      sendButton.setEnabled(true);
+      base.setEnabled(true);
+      base.setFocus(true);
+    } else {
+      base.setEnabled(false);
+      sendButton.setEnabled(sendEnabled);
+      if (sendEnabled) {
+        sendButton.setTitle(null);
+        sendButton.setFocus(true);
+      } else {
+        sendButton.setTitle(Util.C.rebaseNotPossibleMessage());
+        cancelButton.setFocus(true);
+      }
+    }
   }
 
   public String getBase() {
diff --git a/gerrit-server/src/main/java/com/google/gerrit/server/change/ActionJson.java b/gerrit-server/src/main/java/com/google/gerrit/server/change/ActionJson.java
index 023173ed09..df6b76e347 100644
--- a/gerrit-server/src/main/java/com/google/gerrit/server/change/ActionJson.java
+++ b/gerrit-server/src/main/java/com/google/gerrit/server/change/ActionJson.java
@@ -22,6 +22,7 @@ import com.google.gerrit.extensions.restapi.RestView;
 import com.google.gerrit.extensions.webui.PrivateInternals_UiActionDescription;
 import com.google.gerrit.extensions.webui.UiAction;
 import com.google.gerrit.server.CurrentUser;
+import com.google.gerrit.server.changedetail.RebaseChange;
 import com.google.gerrit.server.extensions.webui.UiActions;
 import com.google.gerrit.server.project.ChangeControl;
 import com.google.inject.Inject;
@@ -36,13 +37,16 @@ import java.util.Map;
 public class ActionJson {
   private final Revisions revisions;
   private final DynamicMap<RestView<ChangeResource>> changeViews;
+  private final RebaseChange rebaseChange;
 
   @Inject
   ActionJson(
       Revisions revisions,
-      DynamicMap<RestView<ChangeResource>> changeViews) {
+      DynamicMap<RestView<ChangeResource>> changeViews,
+      RebaseChange rebaseChange) {
     this.revisions = revisions;
     this.changeViews = changeViews;
+    this.rebaseChange = rebaseChange;
   }
 
   public Map<String, ActionInfo> format(RevisionResource rsrc) {
@@ -69,7 +73,7 @@ public class ActionJson {
     Provider<CurrentUser> userProvider = Providers.of(ctl.getCurrentUser());
     for (UiAction.Description d : UiActions.from(
         changeViews,
-        new ChangeResource(ctl),
+        new ChangeResource(ctl, rebaseChange),
         userProvider)) {
       out.put(d.getId(), new ActionInfo(d));
     }
diff --git a/gerrit-server/src/main/java/com/google/gerrit/server/change/ChangeJson.java b/gerrit-server/src/main/java/com/google/gerrit/server/change/ChangeJson.java
index 2accdb847f..367ec2c299 100644
--- a/gerrit-server/src/main/java/com/google/gerrit/server/change/ChangeJson.java
+++ b/gerrit-server/src/main/java/com/google/gerrit/server/change/ChangeJson.java
@@ -92,6 +92,7 @@ import com.google.gerrit.server.IdentifiedUser;
 import com.google.gerrit.server.PatchLineCommentsUtil;
 import com.google.gerrit.server.WebLinks;
 import com.google.gerrit.server.account.AccountLoader;
+import com.google.gerrit.server.changedetail.RebaseChange;
 import com.google.gerrit.server.git.LabelNormalizer;
 import com.google.gerrit.server.notedb.ChangeNotes;
 import com.google.gerrit.server.patch.PatchListNotAvailableException;
@@ -142,6 +143,7 @@ public class ChangeJson {
   private final PatchLineCommentsUtil plcUtil;
   private final Provider<ConsistencyChecker> checkerProvider;
   private final ActionJson actionJson;
+  private final RebaseChange rebaseChange;
 
   private AccountLoader accountLoader;
   private FixInput fix;
@@ -163,7 +165,8 @@ public class ChangeJson {
       ChangeMessagesUtil cmUtil,
       PatchLineCommentsUtil plcUtil,
       Provider<ConsistencyChecker> checkerProvider,
-      ActionJson actionJson) {
+      ActionJson actionJson,
+      RebaseChange rebaseChange) {
     this.db = db;
     this.labelNormalizer = ln;
     this.userProvider = user;
@@ -180,6 +183,7 @@ public class ChangeJson {
     this.plcUtil = plcUtil;
     this.checkerProvider = checkerProvider;
     this.actionJson = actionJson;
+    this.rebaseChange = rebaseChange;
     options = EnumSet.noneOf(ListChangesOption.class);
   }
 
@@ -890,7 +894,7 @@ public class ChangeJson {
         && userProvider.get().isIdentifiedUser()) {
 
       actionJson.addRevisionActions(out,
-          new RevisionResource(new ChangeResource(ctl), in));
+          new RevisionResource(new ChangeResource(ctl, rebaseChange), in));
     }
 
     if (has(DRAFT_COMMENTS)
diff --git a/gerrit-server/src/main/java/com/google/gerrit/server/change/ChangeResource.java b/gerrit-server/src/main/java/com/google/gerrit/server/change/ChangeResource.java
index 16472e35cf..ff4a9f71ac 100644
--- a/gerrit-server/src/main/java/com/google/gerrit/server/change/ChangeResource.java
+++ b/gerrit-server/src/main/java/com/google/gerrit/server/change/ChangeResource.java
@@ -23,6 +23,7 @@ import com.google.gerrit.extensions.restapi.RestView;
 import com.google.gerrit.reviewdb.client.Change;
 import com.google.gerrit.server.CurrentUser;
 import com.google.gerrit.server.IdentifiedUser;
+import com.google.gerrit.server.changedetail.RebaseChange;
 import com.google.gerrit.server.notedb.ChangeNotes;
 import com.google.gerrit.server.project.ChangeControl;
 import com.google.gerrit.server.project.ProjectState;
@@ -36,13 +37,16 @@ public class ChangeResource implements RestResource, HasETag {
       new TypeLiteral<RestView<ChangeResource>>() {};
 
   private final ChangeControl control;
+  private final RebaseChange rebaseChange;
 
-  public ChangeResource(ChangeControl control) {
+  public ChangeResource(ChangeControl control, RebaseChange rebaseChange) {
     this.control = control;
+    this.rebaseChange = rebaseChange;
   }
 
   protected ChangeResource(ChangeResource copy) {
     this.control = copy.control;
+    this.rebaseChange = copy.rebaseChange;
   }
 
   public ChangeControl getControl() {
@@ -66,7 +70,8 @@ public class ChangeResource implements RestResource, HasETag {
       .putBoolean(user.getStarredChanges().contains(getChange().getId()))
       .putInt(user.isIdentifiedUser()
           ? ((IdentifiedUser) user).getAccountId().get()
-          : 0);
+          : 0)
+      .putBoolean(rebaseChange != null && rebaseChange.canRebase(this));
 
     byte[] buf = new byte[20];
     ObjectId noteId;
diff --git a/gerrit-server/src/main/java/com/google/gerrit/server/change/ChangesCollection.java b/gerrit-server/src/main/java/com/google/gerrit/server/change/ChangesCollection.java
index 1648a5dc55..42f16a3a39 100644
--- a/gerrit-server/src/main/java/com/google/gerrit/server/change/ChangesCollection.java
+++ b/gerrit-server/src/main/java/com/google/gerrit/server/change/ChangesCollection.java
@@ -26,6 +26,7 @@ import com.google.gerrit.extensions.restapi.TopLevelResource;
 import com.google.gerrit.reviewdb.client.Change;
 import com.google.gerrit.server.ChangeUtil;
 import com.google.gerrit.server.CurrentUser;
+import com.google.gerrit.server.changedetail.RebaseChange;
 import com.google.gerrit.server.index.ChangeIndexer;
 import com.google.gerrit.server.project.ChangeControl;
 import com.google.gerrit.server.project.NoSuchChangeException;
@@ -49,6 +50,7 @@ public class ChangesCollection implements
   private final ChangeUtil changeUtil;
   private final CreateChange createChange;
   private final ChangeIndexer changeIndexer;
+  private final RebaseChange rebaseChange;
 
   @Inject
   ChangesCollection(
@@ -58,7 +60,8 @@ public class ChangesCollection implements
       DynamicMap<RestView<ChangeResource>> views,
       ChangeUtil changeUtil,
       CreateChange createChange,
-      ChangeIndexer changeIndexer) {
+      ChangeIndexer changeIndexer,
+      RebaseChange rebaseChange) {
     this.user = user;
     this.changeControlFactory = changeControlFactory;
     this.queryFactory = queryFactory;
@@ -66,6 +69,7 @@ public class ChangesCollection implements
     this.changeUtil = changeUtil;
     this.createChange = createChange;
     this.changeIndexer = changeIndexer;
+    this.rebaseChange = rebaseChange;
   }
 
   @Override
@@ -102,7 +106,7 @@ public class ChangesCollection implements
     } catch (NoSuchChangeException e) {
       throw new ResourceNotFoundException(id);
     }
-    return new ChangeResource(control);
+    return new ChangeResource(control, rebaseChange);
   }
 
   public ChangeResource parse(Change.Id id)
@@ -112,7 +116,7 @@ public class ChangesCollection implements
   }
 
   public ChangeResource parse(ChangeControl control) {
-    return new ChangeResource(control);
+    return new ChangeResource(control, rebaseChange);
   }
 
   @SuppressWarnings("unchecked")
diff --git a/gerrit-server/src/main/java/com/google/gerrit/server/change/Rebase.java b/gerrit-server/src/main/java/com/google/gerrit/server/change/Rebase.java
index 4141c24c9c..d2afd9a3ef 100644
--- a/gerrit-server/src/main/java/com/google/gerrit/server/change/Rebase.java
+++ b/gerrit-server/src/main/java/com/google/gerrit/server/change/Rebase.java
@@ -214,12 +214,18 @@ public class Rebase implements RestModifyView<RevisionResource, RebaseInput>,
 
   @Override
   public UiAction.Description getDescription(RevisionResource resource) {
-    return new UiAction.Description()
+    UiAction.Description descr = new UiAction.Description()
       .setLabel("Rebase")
       .setTitle("Rebase onto tip of branch or parent change")
       .setVisible(resource.getChange().getStatus().isOpen()
           && resource.getControl().canRebase()
           && hasOneParent(resource.getPatchSet().getId()));
+    if (descr.isVisible()) {
+      // Disable the rebase button in the RebaseDialog if
+      // the change cannot be rebased.
+      descr.setEnabled(rebaseChange.get().canRebase(resource));
+    }
+    return descr;
   }
 
   public static class CurrentRevision implements
diff --git a/gerrit-server/src/main/java/com/google/gerrit/server/changedetail/RebaseChange.java b/gerrit-server/src/main/java/com/google/gerrit/server/changedetail/RebaseChange.java
index 92f3c00af9..67e70c151b 100644
--- a/gerrit-server/src/main/java/com/google/gerrit/server/changedetail/RebaseChange.java
+++ b/gerrit-server/src/main/java/com/google/gerrit/server/changedetail/RebaseChange.java
@@ -22,11 +22,13 @@ import com.google.gerrit.reviewdb.client.Change.Status;
 import com.google.gerrit.reviewdb.client.ChangeMessage;
 import com.google.gerrit.reviewdb.client.PatchSet;
 import com.google.gerrit.reviewdb.client.PatchSetAncestor;
+import com.google.gerrit.reviewdb.client.Project;
 import com.google.gerrit.reviewdb.client.RevId;
 import com.google.gerrit.reviewdb.server.ReviewDb;
 import com.google.gerrit.server.ChangeUtil;
 import com.google.gerrit.server.GerritPersonIdent;
 import com.google.gerrit.server.IdentifiedUser;
+import com.google.gerrit.server.change.ChangeResource;
 import com.google.gerrit.server.change.PatchSetInserter;
 import com.google.gerrit.server.change.PatchSetInserter.ValidatePolicy;
 import com.google.gerrit.server.change.RevisionResource;
@@ -356,10 +358,21 @@ public class RebaseChange {
     return objectId;
   }
 
+  public boolean canRebase(ChangeResource r) {
+    Change c = r.getChange();
+    return canRebase(c.getProject(), c.currentPatchSetId(), c.getDest());
+  }
+
   public boolean canRebase(RevisionResource r) {
+    return canRebase(r.getChange().getProject(),
+        r.getPatchSet().getId(), r.getChange().getDest());
+  }
+
+  public boolean canRebase(Project.NameKey project,
+      PatchSet.Id patchSetId, Branch.NameKey branch) {
     Repository git;
     try {
-      git = gitManager.openRepository(r.getChange().getProject());
+      git = gitManager.openRepository(project);
     } catch (RepositoryNotFoundException err) {
       return false;
     } catch (IOException err) {
@@ -367,9 +380,9 @@ public class RebaseChange {
     }
     try {
       findBaseRevision(
-          r.getPatchSet().getId(),
+          patchSetId,
           db.get(),
-          r.getChange().getDest(),
+          branch,
           git,
           null,
           null,
diff --git a/gerrit-server/src/test/java/com/google/gerrit/server/change/CommentsTest.java b/gerrit-server/src/test/java/com/google/gerrit/server/change/CommentsTest.java
index 8cd5e253b8..45ac0430a1 100644
--- a/gerrit-server/src/test/java/com/google/gerrit/server/change/CommentsTest.java
+++ b/gerrit-server/src/test/java/com/google/gerrit/server/change/CommentsTest.java
@@ -298,8 +298,8 @@ public class CommentsTest  {
     update.commit();
 
     ChangeControl ctl = stubChangeControl(change);
-    revRes1 = new RevisionResource(new ChangeResource(ctl), ps1);
-    revRes2 = new RevisionResource(new ChangeResource(ctl), ps2);
+    revRes1 = new RevisionResource(new ChangeResource(ctl, null), ps1);
+    revRes2 = new RevisionResource(new ChangeResource(ctl, null), ps2);
   }
 
   private ChangeControl stubChangeControl(Change c) throws OrmException {