Show parent commits on change screen if merge commit is viewed

For reviewing merge commits it may be interesting to look at the
parent commits.

Change-Id: I8d1257ae3ad2649f1a10d87ccd83c0156e31d6f8
Signed-off-by: Edwin Kempin <edwin.kempin@sap.com>

Documentation/user-review-ui.txt

@@ -107,6 +107,10 @@ is also a link to the commit in the Git web browser.
 
 image::images/user-review-ui-change-screen-commit-info.png[width=800, link="images/user-review-ui-change-screen-commit-info.png"]
 
+For merge commits the parent commits are also shown.
+
+image::images/user-review-ui-change-screen-commit-info-merge-commit.png[width=800, link="images/user-review-ui-change-screen-commit-info-merge-commit.png"]
+
 [[change-info]]
 === Change Info Block
 

gerrit-gwtui/src/main/java/com/google/gerrit/client/change/CommitBox.java

@@ -21,11 +21,13 @@ 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.Natives;
 import com.google.gerrit.client.ui.CommentLinkProcessor;
 import com.google.gerrit.client.ui.InlineHyperlink;
 import com.google.gerrit.common.PageLinks;
 import com.google.gerrit.reviewdb.client.Change.Status;
 import com.google.gwt.core.client.GWT;
+import com.google.gwt.core.client.JsArray;
 import com.google.gwt.dom.client.AnchorElement;
 import com.google.gwt.dom.client.Element;
 import com.google.gwt.event.dom.client.ClickEvent;
@@ -33,12 +35,15 @@ import com.google.gwt.resources.client.CssResource;
 import com.google.gwt.uibinder.client.UiBinder;
 import com.google.gwt.uibinder.client.UiField;
 import com.google.gwt.uibinder.client.UiHandler;
+import com.google.gwt.user.client.ui.Anchor;
 import com.google.gwt.user.client.ui.Button;
 import com.google.gwt.user.client.ui.Composite;
+import com.google.gwt.user.client.ui.FlowPanel;
 import com.google.gwt.user.client.ui.HTML;
 import com.google.gwt.user.client.ui.HTMLPanel;
 import com.google.gwt.user.client.ui.ScrollPanel;
 import com.google.gwt.user.client.ui.UIObject;
+import com.google.gwt.user.client.ui.VerticalPanel;
 import com.google.gwtexpui.clippy.client.CopyableLabel;
 import com.google.gwtexpui.safehtml.client.SafeHtmlBuilder;
 
@@ -49,11 +54,16 @@ class CommitBox extends Composite {
   interface Style extends CssResource {
     String collapsed();
     String expanded();
+    String clippy();
+    String parentWebLink();
   }
 
   @UiField Style style;
   @UiField CopyableLabel commitName;
   @UiField AnchorElement browserLink;
+  @UiField Element parents;
+  @UiField FlowPanel parentCommits;
+  @UiField VerticalPanel parentWebLinks;
   @UiField InlineHyperlink authorNameEmail;
   @UiField Element authorDate;
   @UiField InlineHyperlink committerNameEmail;
@@ -108,6 +118,27 @@ class CommitBox extends Composite {
     } else {
       UIObject.setVisible(browserLink, false);
     }
+
+    if (revInfo.commit().parents().length() > 1) {
+      setParents(change.project(), revInfo.commit().parents());
+    }
+  }
+
+  private void setParents(String project, JsArray<CommitInfo> commits) {
+    setVisible(parents, true);
+    for (CommitInfo c : Natives.asList(commits)) {
+      CopyableLabel copyLabel = new CopyableLabel(c.commit());
+      copyLabel.setStyleName(style.clippy());
+      parentCommits.add(copyLabel);
+
+      GitwebLink gw = Gerrit.getGitwebLink();
+      if (gw != null) {
+        Anchor a =
+            new Anchor(gw.toRevision(project, c.commit()), gw.getLinkName());
+        a.setStyleName(style.parentWebLink());
+        parentWebLinks.add(a);
+      }
+    }
   }
 
   private static void formatLink(GitPerson person, InlineHyperlink name,

gerrit-gwtui/src/main/java/com/google/gerrit/client/change/CommitBox.ui.xml

@@ -78,7 +78,11 @@ limitations under the License.
       position: absolute;
       top: 0px;
       right: -16px;
-     }
+    }
+    <!-- To make room for the copyableLabel from the adjacent column -->
+    .parentWebLink {
+      margin-left:16px;
+    }
   </ui:style>
   <g:HTMLPanel>
     <g:ScrollPanel styleName='{style.scroll}' ui:field='scroll'>
@@ -116,6 +120,15 @@ limitations under the License.
         <td><clippy:CopyableLabel styleName='{style.clippy}' ui:field='commitName'/></td>
         <td><a style="margin-left:16px;" ui:field='browserLink' href=""/></td>
       </tr>
+      <tr ui:field='parents' style='display: none'>
+        <th><ui:msg>Parents</ui:msg></th>
+        <td>
+          <g:FlowPanel ui:field='parentCommits'/>
+        </td>
+        <td>
+          <g:VerticalPanel ui:field='parentWebLinks'/>
+        </td>
+      </tr>
       <tr>
         <th><ui:msg>Change-Id</ui:msg></th>
         <td><clippy:CopyableLabel styleName='{style.clippy}' ui:field='idText'/></td>