Make the file tree in merge requests resizable

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/51857

13 files changed, 143 insertions, 42 deletions

diff --git a/app/assets/javascripts/diffs/components/app.vue b/app/assets/javascripts/diffs/components/app.vue
index f0ce2579ee7..8f47931d14a 100644
--- a/app/assets/javascripts/diffs/components/app.vue
+++ b/app/assets/javascripts/diffs/components/app.vue
@@ -4,6 +4,7 @@ import Icon from '~/vue_shared/components/icon.vue';
 import { __ } from '~/locale';
 import createFlash from '~/flash';
 import { GlLoadingIcon } from '@gitlab/ui';
+import PanelResizer from '~/vue_shared/components/panel_resizer.vue';
 import eventHub from '../../notes/event_hub';
 import CompareVersions from './compare_versions.vue';
 import DiffFile from './diff_file.vue';
@@ -11,6 +12,13 @@ import NoChanges from './no_changes.vue';
 import HiddenFilesWarning from './hidden_files_warning.vue';
 import CommitWidget from './commit_widget.vue';
 import TreeList from './tree_list.vue';
+import {
+  TREE_LIST_WIDTH_STORAGE_KEY,
+  INITIAL_TREE_WIDTH,
+  MIN_TREE_WIDTH,
+  MAX_TREE_WIDTH,
+  TREE_HIDE_STATS_WIDTH,
+} from '../constants';
 
 export default {
   name: 'DiffsApp',
@@ -23,6 +31,7 @@ export default {
     CommitWidget,
     TreeList,
     GlLoadingIcon,
+    PanelResizer,
   },
   props: {
     endpoint: {
@@ -54,8 +63,12 @@ export default {
     },
   },
   data() {
+    const treeWidth =
+      parseInt(localStorage.getItem(TREE_LIST_WIDTH_STORAGE_KEY), 10) || INITIAL_TREE_WIDTH;
+
     return {
       assignedDiscussions: false,
+      treeWidth,
     };
   },
   computed: {
@@ -96,6 +109,9 @@ export default {
           this.startVersion.version_index === this.mergeRequestDiff.version_index)
       );
     },
+    hideFileStats() {
+      return this.treeWidth <= TREE_HIDE_STATS_WIDTH;
+    },
   },
   watch: {
     diffViewType() {
@@ -142,6 +158,7 @@ export default {
       'startRenderDiffsQueue',
       'assignDiscussionsToDiff',
       'setHighlightedRow',
+      'cacheTreeListWidth',
     ]),
     fetchData() {
       this.fetchDiffFiles()
@@ -184,6 +201,8 @@ export default {
       }
     },
   },
+  minTreeWidth: MIN_TREE_WIDTH,
+  maxTreeWidth: MAX_TREE_WIDTH,
 };
 </script>
 
@@ -209,7 +228,21 @@ export default {
         :data-can-create-note="getNoteableData.current_user.can_create_note"
         class="files d-flex prepend-top-default"
       >
-        <div v-show="showTreeList" class="diff-tree-list"><tree-list /></div>
+        <div
+          v-show="showTreeList"
+          :style="{ width: `${treeWidth}px` }"
+          class="diff-tree-list js-diff-tree-list"
+        >
+          <panel-resizer
+            :size.sync="treeWidth"
+            :start-size="treeWidth"
+            :min-size="$options.minTreeWidth"
+            :max-size="$options.maxTreeWidth"
+            side="right"
+            @resize-end="cacheTreeListWidth"
+          />
+          <tree-list :hide-file-stats="hideFileStats" />
+        </div>
         <div class="diff-files-holder">
           <commit-widget v-if="commit" :commit="commit" />
           <template v-if="renderDiffFiles">
diff --git a/app/assets/javascripts/diffs/components/tree_list.vue b/app/assets/javascripts/diffs/components/tree_list.vue
index 7e00b994541..8fc3af15bea 100644
--- a/app/assets/javascripts/diffs/components/tree_list.vue
+++ b/app/assets/javascripts/diffs/components/tree_list.vue
@@ -13,6 +13,12 @@ export default {
     Icon,
     FileRow,
   },
+  props: {
+    hideFileStats: {
+      type: Boolean,
+      required: true,
+    },
+  },
   data() {
     return {
       search: '',
@@ -40,6 +46,9 @@ export default {
         return acc;
       }, []);
     },
+    fileRowExtraComponent() {
+      return this.hideFileStats ? null : FileRowStats;
+    },
   },
   methods: {
     ...mapActions('diffs', ['toggleTreeOpen', 'scrollToFile', 'toggleFileFinder']),
@@ -48,7 +57,6 @@ export default {
     },
   },
   shortcutKeyCharacter: `${/Mac/i.test(navigator.userAgent) ? '&#8984;' : 'Ctrl'}+P`,
-  FileRowStats,
   diffTreeFiltering: gon.features && gon.features.diffTreeFiltering,
 };
 </script>
@@ -98,7 +106,7 @@ export default {
           :file="file"
           :level="0"
           :hide-extra-on-tree="true"
-          :extra-component="$options.FileRowStats"
+          :extra-component="fileRowExtraComponent"
           :show-changed-icon="true"
           @toggleTreeOpen="toggleTreeOpen"
           @clickFile="scrollToFile"
diff --git a/app/assets/javascripts/diffs/constants.js b/app/assets/javascripts/diffs/constants.js
index bd188d9de9e..7002655ea49 100644
--- a/app/assets/javascripts/diffs/constants.js
+++ b/app/assets/javascripts/diffs/constants.js
@@ -36,3 +36,9 @@ export const MR_TREE_SHOW_KEY = 'mr_tree_show';
 export const TREE_TYPE = 'tree';
 export const TREE_LIST_STORAGE_KEY = 'mr_diff_tree_list';
 export const WHITESPACE_STORAGE_KEY = 'mr_show_whitespace';
+export const TREE_LIST_WIDTH_STORAGE_KEY = 'mr_tree_list_width';
+
+export const INITIAL_TREE_WIDTH = 320;
+export const MIN_TREE_WIDTH = 240;
+export const MAX_TREE_WIDTH = 400;
+export const TREE_HIDE_STATS_WIDTH = 260;
diff --git a/app/assets/javascripts/diffs/store/actions.js b/app/assets/javascripts/diffs/store/actions.js
index 7fb66ce433b..c6a691d52b0 100644
--- a/app/assets/javascripts/diffs/store/actions.js
+++ b/app/assets/javascripts/diffs/store/actions.js
@@ -16,6 +16,7 @@ import {
   MR_TREE_SHOW_KEY,
   TREE_LIST_STORAGE_KEY,
   WHITESPACE_STORAGE_KEY,
+  TREE_LIST_WIDTH_STORAGE_KEY,
 } from '../constants';
 
 export const setBaseConfig = ({ commit }, options) => {
@@ -300,5 +301,9 @@ export const toggleFileFinder = ({ commit }, visible) => {
   commit(types.TOGGLE_FILE_FINDER_VISIBLE, visible);
 };
 
+export const cacheTreeListWidth = (_, size) => {
+  localStorage.setItem(TREE_LIST_WIDTH_STORAGE_KEY, size);
+};
+
 // prevent babel-plugin-rewire from generating an invalid default during karma tests
 export default () => {};
diff --git a/app/assets/javascripts/vue_shared/components/panel_resizer.vue b/app/assets/javascripts/vue_shared/components/panel_resizer.vue
index bf736a378dd..8d81940eb91 100644
--- a/app/assets/javascripts/vue_shared/components/panel_resizer.vue
+++ b/app/assets/javascripts/vue_shared/components/panel_resizer.vue
@@ -28,11 +28,12 @@ export default {
   data() {
     return {
       size: this.startSize,
+      isDragging: false,
     };
   },
   computed: {
     className() {
-      return `drag-${this.side}`;
+      return [`position-${this.side}-0`, { 'is-dragging': this.isDragging }];
     },
     cursorStyle() {
       if (this.enabled) {
@@ -57,6 +58,7 @@ export default {
     startDrag(e) {
       if (this.enabled) {
         e.preventDefault();
+        this.isDragging = true;
         this.startPos = e.clientX;
         this.currentStartSize = this.size;
         document.addEventListener('mousemove', this.drag);
@@ -80,6 +82,7 @@ export default {
     },
     endDrag(e) {
       e.preventDefault();
+      this.isDragging = false;
       document.removeEventListener('mousemove', this.drag);
       this.$emit('resize-end', this.size);
     },
@@ -91,7 +94,7 @@ export default {
   <div
     :class="className"
     :style="cursorStyle"
-    class="drag-handle"
+    class="position-absolute position-top-0 position-bottom-0 drag-handle"
     @mousedown="startDrag"
     @dblclick="resetSize"
   ></div>
diff --git a/app/assets/stylesheets/framework/common.scss b/app/assets/stylesheets/framework/common.scss
index c5c3b66438c..2179743feb0 100644
--- a/app/assets/stylesheets/framework/common.scss
+++ b/app/assets/stylesheets/framework/common.scss
@@ -442,3 +442,15 @@ img.emoji {
 .position-left-0 { left: 0; }
 .position-right-0 { right: 0; }
 .position-top-0 { top: 0; }
+
+.drag-handle {
+  width: 4px;
+
+  &:hover {
+    background-color: $white-normal;
+  }
+
+  &.is-dragging {
+    background-color: $gray-600;
+  }
+}
diff --git a/app/assets/stylesheets/page_bundles/ide.scss b/app/assets/stylesheets/page_bundles/ide.scss
index 2ac98b5d18f..a80158943c6 100644
--- a/app/assets/stylesheets/page_bundles/ide.scss
+++ b/app/assets/stylesheets/page_bundles/ide.scss
@@ -682,25 +682,6 @@ $ide-commit-header-height: 48px;
   flex: 1;
 }
 
-.drag-handle {
-  position: absolute;
-  top: 0;
-  bottom: 0;
-  width: 4px;
-
-  &:hover {
-    background-color: $white-normal;
-  }
-
-  &.drag-right {
-    right: 0;
-  }
-
-  &.drag-left {
-    left: 0;
-  }
-}
-
 .ide-commit-list-container {
   display: flex;
   flex: 1;
diff --git a/app/assets/stylesheets/pages/diff.scss b/app/assets/stylesheets/pages/diff.scss
index a708149b36c..ae0768592e0 100644
--- a/app/assets/stylesheets/pages/diff.scss
+++ b/app/assets/stylesheets/pages/diff.scss
@@ -1038,12 +1038,30 @@
 }
 
 .diff-tree-list {
-  width: 320px;
+  position: -webkit-sticky;
+  position: sticky;
+  $top-pos: $header-height + $mr-tabs-height + $mr-version-controls-height + 10px;
+  top: $header-height + $mr-tabs-height + $mr-version-controls-height + 10px;
+  max-height: calc(100vh - #{$top-pos});
+  padding-right: $gl-padding;
+  z-index: 202;
+
+  .with-performance-bar & {
+    $performance-bar-top-pos: $performance-bar-height + $top-pos;
+    top: $performance-bar-top-pos;
+    max-height: calc(100vh - #{$performance-bar-top-pos});
+  }
+
+  .drag-handle {
+    bottom: 16px;
+    transform: translateX(-6px);
+  }
 }
 
 .diff-files-holder {
   flex: 1;
   min-width: 0;
+  z-index: 201;
 }
 
 .compare-versions-container {
@@ -1051,23 +1069,12 @@
 }
 
 .tree-list-holder {
-  position: -webkit-sticky;
-  position: sticky;
-  $top-pos: $header-height + $mr-tabs-height + $mr-version-controls-height + 10px;
-  top: $header-height + $mr-tabs-height + $mr-version-controls-height + 10px;
-  max-height: calc(100vh - #{$top-pos});
-  padding-right: $gl-padding;
+  height: 100%;
 
   .file-row {
     margin-left: 0;
     margin-right: 0;
   }
-
-  .with-performance-bar & {
-    $performance-bar-top-pos: $performance-bar-height + $top-pos;
-    top: $performance-bar-top-pos;
-    max-height: calc(100vh - #{$performance-bar-top-pos});
-  }
 }
 
 .tree-list-scroll {
diff --git a/app/assets/stylesheets/pages/merge_requests.scss b/app/assets/stylesheets/pages/merge_requests.scss
index 790d438c7e2..883c856870f 100644
--- a/app/assets/stylesheets/pages/merge_requests.scss
+++ b/app/assets/stylesheets/pages/merge_requests.scss
@@ -735,7 +735,7 @@
 
 .mr-version-controls {
   position: relative;
-  z-index: 103;
+  z-index: 203;
   background: $gray-light;
   color: $gl-text-color;
   margin-top: -1px;
@@ -809,7 +809,7 @@
 
 .merge-request-tabs-holder {
   top: $header-height;
-  z-index: 200;
+  z-index: 300;
   background-color: $white-light;
   border-bottom: 1px solid $border-color;
 
diff --git a/changelogs/unreleased/diff-tree-resizable.yml b/changelogs/unreleased/diff-tree-resizable.yml
new file mode 100644
index 00000000000..7411640aea5
--- /dev/null
+++ b/changelogs/unreleased/diff-tree-resizable.yml
@@ -0,0 +1,5 @@
+---
+title: Make file tree in merge requests resizable
+merge_request:
+author:
+type: added
diff --git a/spec/javascripts/diffs/components/app_spec.js b/spec/javascripts/diffs/components/app_spec.js
index a2cbc0f3c72..5abdfe695d0 100644
--- a/spec/javascripts/diffs/components/app_spec.js
+++ b/spec/javascripts/diffs/components/app_spec.js
@@ -68,6 +68,32 @@ describe('diffs/components/app', () => {
     });
   });
 
+  describe('resizable', () => {
+    afterEach(() => {
+      localStorage.removeItem('mr_tree_list_width');
+    });
+
+    it('sets initial width when no localStorage has been set', () => {
+      createComponent();
+
+      expect(vm.vm.treeWidth).toEqual(320);
+    });
+
+    it('sets initial width to localStorage size', () => {
+      localStorage.setItem('mr_tree_list_width', '200');
+
+      createComponent();
+
+      expect(vm.vm.treeWidth).toEqual(200);
+    });
+
+    it('sets width of tree list', () => {
+      createComponent();
+
+      expect(vm.find('.js-diff-tree-list').element.style.width).toEqual('320px');
+    });
+  });
+
   describe('empty state', () => {
     it('renders empty state when no diff files exist', () => {
       createComponent();
diff --git a/spec/javascripts/diffs/components/tree_list_spec.js b/spec/javascripts/diffs/components/tree_list_spec.js
index 9e556698f34..cd7bf6405e5 100644
--- a/spec/javascripts/diffs/components/tree_list_spec.js
+++ b/spec/javascripts/diffs/components/tree_list_spec.js
@@ -28,7 +28,7 @@ describe('Diffs tree list component', () => {
 
     localStorage.removeItem('mr_diff_tree_list');
 
-    vm = mountComponentWithStore(Component, { store });
+    vm = mountComponentWithStore(Component, { store, props: { hideFileStats: false } });
   });
 
   afterEach(() => {
@@ -77,6 +77,16 @@ describe('Diffs tree list component', () => {
       expect(vm.$el.querySelectorAll('.file-row')[1].textContent).toContain('app');
     });
 
+    it('hides file stats', done => {
+      vm.hideFileStats = true;
+
+      vm.$nextTick(() => {
+        expect(vm.$el.querySelector('.file-row-stats')).toBe(null);
+
+        done();
+      });
+    });
+
     it('calls toggleTreeOpen when clicking folder', () => {
       spyOn(vm.$store, 'dispatch').and.stub();
 
diff --git a/spec/javascripts/vue_shared/components/panel_resizer_spec.js b/spec/javascripts/vue_shared/components/panel_resizer_spec.js
index 49a580be06b..caabe3aa260 100644
--- a/spec/javascripts/vue_shared/components/panel_resizer_spec.js
+++ b/spec/javascripts/vue_shared/components/panel_resizer_spec.js
@@ -44,7 +44,10 @@ describe('Panel Resizer component', () => {
     });
 
     expect(vm.$el.tagName).toEqual('DIV');
-    expect(vm.$el.getAttribute('class')).toBe('drag-handle drag-left');
+    expect(vm.$el.getAttribute('class')).toBe(
+      'position-absolute position-top-0 position-bottom-0 drag-handle position-left-0',
+    );
+
     expect(vm.$el.getAttribute('style')).toBe('cursor: ew-resize;');
   });
 
@@ -55,7 +58,9 @@ describe('Panel Resizer component', () => {
     });
 
     expect(vm.$el.tagName).toEqual('DIV');
-    expect(vm.$el.getAttribute('class')).toBe('drag-handle drag-right');
+    expect(vm.$el.getAttribute('class')).toBe(
+      'position-absolute position-top-0 position-bottom-0 drag-handle position-right-0',
+    );
   });
 
   it('drag the resizer', () => {