Expand unresolved comment threads in diff view by default

This change leverages the unresolved flag to automatically expand only
the last UNRESOLVED_EXPAND_COUNT comments in unresolved threads.

Feature: Issue 4752
Change-Id: Ia23920e1a210246838645d56a6bc81d0dff7da07

polygerrit-ui/app/elements/diff/gr-diff-comment-thread/gr-diff-comment-thread.js

@@ -14,6 +14,7 @@
 (function() {
   'use strict';
 
+  var UNRESOLVED_EXPAND_COUNT = 5;
   var NEWLINE_PATTERN = /\n/g;
 
   Polymer({
@@ -71,6 +72,7 @@
       this._getLoggedIn().then(function(loggedIn) {
         this._showActions = loggedIn;
       }.bind(this));
+      this._setInitialExpandedState();
     },
 
     addOrEditDraft: function(opt_lineNum) {
@@ -125,6 +127,21 @@
       });
     },
 
+    /**
+     * Sets the initial state of the comment thread to have the last
+     * {UNRESOLVED_EXPAND_COUNT} comments expanded by default if the
+     * thread is unresolved.
+     */
+    _setInitialExpandedState: function() {
+      var comment;
+      for (var i = 0; i < this._orderedComments.length; i++) {
+        comment = this._orderedComments[i];
+        comment.collapsed =
+            this._orderedComments.length - i - 1 >= UNRESOLVED_EXPAND_COUNT ||
+            !this._unresolved;
+      }
+    },
+
     _sortedComments: function(comments) {
       return comments.slice().sort(function(c1, c2) {
         var c1Date = c1.__date || util.parseDate(c1.updated);

polygerrit-ui/app/elements/diff/gr-diff-comment-thread/gr-diff-comment-thread_test.html

@@ -40,6 +40,7 @@ limitations under the License.
 <script>
   suite('gr-diff-comment-thread tests', function() {
     var element;
+
     setup(function() {
       stub('gr-rest-api-interface', {
         getLoggedIn: function() { return Promise.resolve(false); },
@@ -465,6 +466,10 @@ limitations under the License.
     });
 
     suite('jack and sally comment data test consolidation', function() {
+      var getComments = function() {
+        return Polymer.dom(element.root).querySelectorAll('gr-diff-comment');
+      };
+
       setup(function() {
         element.comments = [
         {
@@ -518,6 +523,21 @@ limitations under the License.
         flushAsynchronousOperations();
         assert.isTrue(element._unresolved);
       });
+
+      test('_setInitialExpandedState', function() {
+        element._unresolved = true;
+        element._setInitialExpandedState();
+        var comments = getComments();
+        for (var i = 0; i < element.comments.length; i++) {
+          assert.isFalse(element.comments[i].collapsed);
+        }
+        element._unresolved = false;
+        element._setInitialExpandedState();
+        var comments = getComments();
+        for (var i = 0; i < element.comments.length; i++) {
+          assert.isTrue(element.comments[i].collapsed);
+        }
+      });
     });
 
     test('_computeHostClass', function() {

polygerrit-ui/app/elements/diff/gr-diff-comment/gr-diff-comment.js

@@ -131,6 +131,8 @@
     attached: function() {
       if (this.editing) {
         this.collapsed = false;
+      } else if (this.comment) {
+        this.collapsed = this.comment.collapsed;
       }
     },