Fix support to use "Default Base For Merges" preference

* This implements the setting.

* This also uses it for picking rather to show Parent 1 or Auto Merge first.

Bug: Issue 8838
Change-Id: I6888b449acb285081db427119990120eb8875e6c

8 files changed, 77 insertions, 19 deletions

diff --git a/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view.html b/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view.html
index 4f5bf94795..82279bd5fb 100644
--- a/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view.html
+++ b/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view.html
@@ -40,6 +40,7 @@ limitations under the License.
 <link rel="import" href="../../shared/gr-overlay/gr-overlay.html">
 <link rel="import" href="../../shared/gr-rest-api-interface/gr-rest-api-interface.html">
 <link rel="import" href="../../shared/gr-tooltip-content/gr-tooltip-content.html">
+<link rel="import" href="../../shared/revision-info/revision-info.html">
 <link rel="import" href="../gr-change-actions/gr-change-actions.html">
 <link rel="import" href="../gr-change-metadata/gr-change-metadata.html">
 <link rel="import" href="../gr-commit-info/gr-commit-info.html">
@@ -525,6 +526,7 @@ limitations under the License.
             all-patch-sets="[[_allPatchSets]]"
             change="[[_change]]"
             change-num="[[_changeNum]]"
+            revision-info="[[_revisionInfo]]"
             change-comments="[[_changeComments]]"
             commit-info="[[_commitInfo]]"
             change-url="[[_computeChangeUrl(_change)]]"
diff --git a/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view.js b/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view.js
index 909a1ee0ec..470f8596c1 100644
--- a/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view.js
+++ b/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view.js
@@ -122,6 +122,7 @@
         type: Object,
         value: {},
       },
+      _prefs: Object,
       /** @type {?} */
       _changeComments: Object,
       _canStartReview: {
@@ -134,6 +135,10 @@
         type: Object,
         observer: '_changeChanged',
       },
+      _revisionInfo: {
+        type: Object,
+        computed: '_getRevisionInfo(_change)',
+      },
       /** @type {?} */
       _commitInfo: Object,
       _currentRevision: {
@@ -262,6 +267,7 @@
       'fullscreen-overlay-closed': '_handleShowBackgroundContent',
       'diff-comments-modified': '_handleReloadCommentThreads',
     },
+
     observers: [
       '_labelsChanged(_change.labels.*)',
       '_paramsAndChangeChanged(params, _change)',
@@ -335,7 +341,7 @@
     _setDiffViewMode(opt_reset) {
       if (!opt_reset && this.viewState.diffViewMode) { return; }
 
-      return this.$.restAPI.getPreferences().then( prefs => {
+      return this._getPreferences().then( prefs => {
         if (!this.viewState.diffMode) {
           this.set('viewState.diffMode', prefs.default_diff_view);
         }
@@ -790,10 +796,11 @@
 
     _changeChanged(change) {
       if (!change || !this._patchRange || !this._allPatchSets) { return; }
-      this.set('_patchRange.basePatchNum',
-          this._patchRange.basePatchNum || 'PARENT');
-      this.set('_patchRange.patchNum',
-          this._patchRange.patchNum ||
+
+      const parent = this._getBasePatchNum(change, this._patchRange);
+
+      this.set('_patchRange.basePatchNum', parent);
+      this.set('_patchRange.patchNum', this._patchRange.patchNum ||
               this.computeLatestPatchNum(this._allPatchSets));
 
       // Reset the related changes toggle in the event it was previously
@@ -804,6 +811,35 @@
       this.fire('title-change', {title});
     },
 
+    /**
+     * Gets base patch number, if is a parent try and
+     * decide from preference weather to default to `auto merge`
+     * or `Parent 1`.
+     * @param {Object} change
+     * @param {Object} patchRange
+     * @return {number|string}
+     */
+    _getBasePatchNum(change, patchRange) {
+      if (patchRange.basePatchNum &&
+          patchRange.basePatchNum !== 'PARENT') {
+        return patchRange.basePatchNum;
+      }
+
+      const revisionInfo = this._getRevisionInfo(change);
+      if (!revisionInfo) return 'PARENT';
+
+      const parentCounts = revisionInfo.getParentCountMap();
+      // check that there is at least 2 parents otherwise fall back to 1,
+      // which means there is only one parent.
+      const parentCount = parentCounts.hasOwnProperty(1) ?
+          parentCounts[1] : 1;
+
+      const preferFirst = this._prefs &&
+          this._prefs.default_base_for_merges === 'FIRST_PARENT';
+
+      return parentCount > 1 && preferFirst ? -1 : 'PARENT';
+    },
+
     _computeChangeUrl(change) {
       return Gerrit.Nav.getUrlForChange(change);
     },
@@ -1057,6 +1093,10 @@
           });
     },
 
+    _getPreferences() {
+      return this.$.restAPI.getPreferences();
+    },
+
     _updateRebaseAction(revisionActions) {
       if (revisionActions && revisionActions.rebase) {
         revisionActions.rebase.rebaseOnCurrent =
@@ -1110,9 +1150,12 @@
       const detailCompletes = this.$.restAPI.getChangeDetail(
           this._changeNum, this._handleGetChangeDetailError.bind(this));
       const editCompletes = this._getEdit();
+      const prefCompletes = this._getPreferences();
+
+      return Promise.all([detailCompletes, editCompletes, prefCompletes])
+          .then(([change, edit, prefs]) => {
+            this._prefs = prefs;
 
-      return Promise.all([detailCompletes, editCompletes])
-          .then(([change, edit]) => {
             if (!change) {
               return '';
             }
@@ -1661,6 +1704,10 @@
           e.detail.starred);
     },
 
+    _getRevisionInfo(change) {
+      return new Gerrit.RevisionInfo(change);
+    },
+
     _computeCurrentRevision(currentRevision, revisions) {
       return revisions && revisions[currentRevision];
     },
diff --git a/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view_test.html b/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view_test.html
index f6acef68a1..926895b1fb 100644
--- a/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view_test.html
+++ b/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view_test.html
@@ -1580,8 +1580,8 @@ limitations under the License.
     });
 
     test('_selectedRevision updates when patchNum is changed', () => {
-      const revision1 = {_number: 1, commit: {}};
-      const revision2 = {_number: 2, commit: {}};
+      const revision1 = {_number: 1, commit: {parents: []}};
+      const revision2 = {_number: 2, commit: {parents: []}};
       sandbox.stub(element.$.restAPI, 'getChangeDetail').returns(
           Promise.resolve({
             revisions: {
@@ -1594,6 +1594,7 @@ limitations under the License.
             change_id: 'loremipsumdolorsitamet',
           }));
       sandbox.stub(element, '_getEdit').returns(Promise.resolve());
+      sandbox.stub(element, '_getPreferences').returns(Promise.resolve({}));
       element._patchRange = {patchNum: '2'};
       return element._getChangeDetail().then(() => {
         assert.strictEqual(element._selectedRevision, revision2);
diff --git a/polygerrit-ui/app/elements/change/gr-file-list-header/gr-file-list-header.html b/polygerrit-ui/app/elements/change/gr-file-list-header/gr-file-list-header.html
index 142e706b00..22c476cc42 100644
--- a/polygerrit-ui/app/elements/change/gr-file-list-header/gr-file-list-header.html
+++ b/polygerrit-ui/app/elements/change/gr-file-list-header/gr-file-list-header.html
@@ -28,7 +28,6 @@ limitations under the License.
 <link rel="import" href="../../shared/gr-select/gr-select.html">
 <link rel="import" href="../../shared/gr-button/gr-button.html">
 <link rel="import" href="../../shared/gr-icons/gr-icons.html">
-<link rel="import" href="../../shared/revision-info/revision-info.html">
 <link rel="import" href="../gr-file-list-constants.html">
 
 <dom-module id="gr-file-list-header">
@@ -164,7 +163,7 @@ limitations under the License.
               base-patch-num="[[basePatchNum]]"
               available-patches="[[allPatchSets]]"
               revisions="[[change.revisions]]"
-              revision-info="[[_revisionInfo]]"
+              revision-info="[[revisionInfo]]"
               on-patch-range-change="_handlePatchChange">
           </gr-patch-range-select>
           <span class="separator"></span>
diff --git a/polygerrit-ui/app/elements/change/gr-file-list-header/gr-file-list-header.js b/polygerrit-ui/app/elements/change/gr-file-list-header/gr-file-list-header.js
index 665472bcfc..c6e369c0cc 100644
--- a/polygerrit-ui/app/elements/change/gr-file-list-header/gr-file-list-header.js
+++ b/polygerrit-ui/app/elements/change/gr-file-list-header/gr-file-list-header.js
@@ -84,10 +84,7 @@
         type: Boolean,
         computed: '_computeDescriptionReadOnly(loggedIn, change, account)',
       },
-      _revisionInfo: {
-        type: Object,
-        computed: '_getRevisionInfo(change)',
-      },
+      revisionInfo: Object,
     },
 
     behaviors: [
@@ -230,10 +227,6 @@
       return 'patchInfoOldPatchSet';
     },
 
-    _getRevisionInfo(change) {
-      return new Gerrit.RevisionInfo(change);
-    },
-
     _hideIncludedIn(change) {
       return change && change.status === MERGED_STATUS ? '' : 'hide';
     },
diff --git a/polygerrit-ui/app/elements/settings/gr-settings-view/gr-settings-view.html b/polygerrit-ui/app/elements/settings/gr-settings-view/gr-settings-view.html
index 799cf5943b..be7f3da842 100644
--- a/polygerrit-ui/app/elements/settings/gr-settings-view/gr-settings-view.html
+++ b/polygerrit-ui/app/elements/settings/gr-settings-view/gr-settings-view.html
@@ -194,6 +194,18 @@ limitations under the License.
               </gr-select>
             </span>
           </section>
+          <section hidden$="[[!_localPrefs.default_base_for_merges]]">
+            <span class="title">Default Base For Merges</span>
+            <span class="value">
+              <gr-select
+                  bind-value="{{_localPrefs.default_base_for_merges}}">
+                <select>
+                  <option value="AUTO_MERGE">Auto Merge</option>
+                  <option value="FIRST_PARENT">First Parent</option>
+                </select>
+              </gr-select>
+            </span>
+          </section>
           <section>
             <span class="title">Diff view</span>
             <span class="value">
diff --git a/polygerrit-ui/app/elements/settings/gr-settings-view/gr-settings-view.js b/polygerrit-ui/app/elements/settings/gr-settings-view/gr-settings-view.js
index 0ce8ce0c80..ec98ad8778 100644
--- a/polygerrit-ui/app/elements/settings/gr-settings-view/gr-settings-view.js
+++ b/polygerrit-ui/app/elements/settings/gr-settings-view/gr-settings-view.js
@@ -25,6 +25,7 @@
     'diff_view',
     'publish_comments_on_push',
     'work_in_progress_by_default',
+    'default_base_for_merges',
     'signed_off_by',
     'email_format',
     'size_bar_in_change_table',
diff --git a/polygerrit-ui/app/elements/settings/gr-settings-view/gr-settings-view_test.html b/polygerrit-ui/app/elements/settings/gr-settings-view/gr-settings-view_test.html
index f47816f4b1..9864a864a2 100644
--- a/polygerrit-ui/app/elements/settings/gr-settings-view/gr-settings-view_test.html
+++ b/polygerrit-ui/app/elements/settings/gr-settings-view/gr-settings-view_test.html
@@ -88,6 +88,7 @@ limitations under the License.
         diff_view: 'UNIFIED_DIFF',
         email_strategy: 'ENABLED',
         email_format: 'HTML_PLAINTEXT',
+        default_base_for_merges: 'FIRST_PARENT',
         size_bar_in_change_table: true,
 
         my: [
@@ -168,6 +169,8 @@ limitations under the License.
           .firstElementChild.bindValue, preferences.email_strategy);
       assert.equal(valueOf('Email format', 'preferences')
           .firstElementChild.bindValue, preferences.email_format);
+      assert.equal(valueOf('Default Base For Merges', 'preferences')
+          .firstElementChild.bindValue, preferences.default_base_for_merges);
       assert.equal(valueOf('Diff view', 'preferences')
           .firstElementChild.bindValue, preferences.diff_view);
       assert.equal(valueOf('Show size bars in file list', 'preferences')