Change rebase action behavior

Previously, if the server did not return enabled=true for the rebase
change action, the rebase button would be disabled on the UI. Really,
what disabled indicated in this case was that the rebase could not be
performed on the current branch, but could still perform a rebase on
a different parent revision.

This change updates revision actions in the change view always be
enabled, and introduces a new parameter to indicate whether or not
rebasing should be enabled on the current branch based on the initial
status of the enabled flag.

This change also disables the rebase button on the rebase dialog until
an option is explicitly chosen. Previously, if an option was not chosen,
if rebase was clicked, it would submit with a base branch of '', which
is the same thing checking the box accomplishes. Now, either the box
must be checked, or a base change must be entered, so it is more clear
what happens with the rebase and in the new scenario when you cannot
submit on the base branch, there won't be a possibility of a server
error.

Bug: Issue 5126
Change-Id: I47083ad328095aad4e04f2fc1586ad4d34412e4c

polygerrit-ui/app/elements/change/gr-change-view/gr-change-view.html

@@ -267,6 +267,7 @@ limitations under the License.
             <gr-change-actions id="actions"
                 change="[[_change]]"
                 actions="[[_change.actions]]"
+                rebase-on-current="[[_rebaseOnCurrent]]"
                 revision-actions="[[_currentRevisionActions]]"
                 change-num="[[_changeNum]]"
                 change-status="[[_change.status]]"

polygerrit-ui/app/elements/change/gr-change-view/gr-change-view.js

@@ -96,6 +96,7 @@
       },
       _loading: Boolean,
       _projectConfig: Object,
+      _rebaseOnCurrent: Boolean,
       _replyButtonLabel: {
         type: String,
         value: 'Reply',
@@ -710,6 +711,14 @@
           }.bind(this));
     },
 
+    _updateRebaseAction: function(revisionActions) {
+      if (revisionActions && revisionActions.rebase){
+        this._rebaseOnCurrent = !!revisionActions.rebase.enabled;
+        revisionActions.rebase.enabled = true;
+      }
+      return revisionActions;
+    },
+
     _getChangeDetail: function() {
       return this.$.restAPI.getChangeDetail(this._changeNum,
           this._handleGetChangeDetailError.bind(this)).then(
@@ -735,7 +744,8 @@
                     currentRevision.commit.commit = latestRevisionSha;
                   }
                   this._commitInfo = currentRevision.commit;
-                  this._currentRevisionActions = currentRevision.actions;
+                  this._currentRevisionActions =
+                      this._updateRebaseAction(currentRevision.actions);
                   // TODO: Fetch and process files.
                 }
               }.bind(this));

polygerrit-ui/app/elements/change/gr-change-view/gr-change-view_test.html

@@ -180,6 +180,41 @@ limitations under the License.
       assert.equal(putDescStub.args[0][2], 'test2');
     });
 
+    test('_updateRebaseAction', function(){
+      var currentRevisionActions = {
+        cherrypick: {
+          enabled: true,
+          label: 'Cherry Pick',
+          method: 'POST',
+          title: 'cherrypick'
+        },
+        rebase: {
+          enabled: true,
+          label: 'Rebase',
+          method: 'POST',
+          title: 'Rebase onto tip of branch or parent change'
+        },
+      };
+
+      // Rebase enabled should always end up true.
+      // When rebase is enabled initially, rebaseOnCurrent should be set to
+      // true.
+      assert.equal(element._updateRebaseAction(currentRevisionActions),
+        currentRevisionActions);
+
+      assert.isTrue(element._rebaseOnCurrent);
+
+      var newRevisionActions = currentRevisionActions
+      delete newRevisionActions.rebase.enabled;
+
+      // When rebase is not enabled initially, rebaseOnCurrent should be set to
+      // false.
+      assert.equal(element._updateRebaseAction(newRevisionActions),
+        currentRevisionActions);
+
+      assert.isFalse(element._rebaseOnCurrent);
+    });
+
     test('_reload is called when an approved label is removed', function() {
       var vote = {_account_id: 1, name: 'bojack', value: 1};
       element._changeNum = '42';