Add drag to select lines

Updates mr diffs to use draggable events to select lines for comment

app/assets/javascripts/diffs/components/diff_line_note_form.vue

@@ -56,10 +56,11 @@ export default {
   },
   computed: {
     ...mapState({
-      noteableData: (state) => state.notes.noteableData,
-      diffViewType: (state) => state.diffs.diffViewType,
+      diffViewType: ({ diffs }) => diffs.diffViewType,
+      showSuggestPopover: ({ diffs }) => diffs.showSuggestPopover,
+      noteableData: ({ notes }) => notes.noteableData,
+      selectedCommentPosition: ({ notes }) => notes.selectedCommentPosition,
     }),
-    ...mapState('diffs', ['showSuggestPopover']),
     ...mapGetters('diffs', ['getDiffFileByHash', 'diffLines']),
     ...mapGetters([
       'isLoggedIn',
@@ -126,6 +127,10 @@ export default {
 
       this.initAutoSave(this.noteableData, keys);
     }
+
+    if (this.selectedCommentPosition) {
+      this.commentLineStart = this.selectedCommentPosition.start;
+    }
   },
   methods: {
     ...mapActions('diffs', [

app/assets/javascripts/diffs/components/diff_row.vue

@@ -10,6 +10,7 @@ import {
   CONFLICT_THEIR,
   CONFLICT_MARKER,
 } from '../constants';
+import glFeatureFlagsMixin from '~/vue_shared/mixins/gl_feature_flags_mixin';
 import DiffGutterAvatars from './diff_gutter_avatars.vue';
 import * as utils from './diff_row_utils';
 
@@ -22,6 +23,7 @@ export default {
     GlTooltip: GlTooltipDirective,
     SafeHtml,
   },
+  mixins: [glFeatureFlagsMixin()],
   props: {
     fileHash: {
       type: String,
@@ -45,6 +47,15 @@ export default {
       required: false,
       default: false,
     },
+    index: {
+      type: Number,
+      required: true,
+    },
+  },
+  data() {
+    return {
+      dragging: false,
+    };
   },
   computed: {
     ...mapGetters('diffs', ['fileLineCoverage']),
@@ -52,26 +63,35 @@ export default {
     ...mapState({
       isHighlighted(state) {
         const line = this.line.left?.line_code ? this.line.left : this.line.right;
-        return utils.isHighlighted(state, line, this.isCommented);
+        return utils.isHighlighted(state, line, false);
       },
     }),
     classNameMap() {
       return {
         [CONTEXT_LINE_CLASS_NAME]: this.line.isContextLineLeft,
         [PARALLEL_DIFF_VIEW_TYPE]: !this.inline,
+        commented: this.isCommented,
       };
     },
     parallelViewLeftLineType() {
-      return utils.parallelViewLeftLineType(this.line, this.isHighlighted);
+      return utils.parallelViewLeftLineType(this.line, this.isHighlighted || this.isCommented);
     },
     coverageState() {
       return this.fileLineCoverage(this.filePath, this.line.right.new_line);
     },
     classNameMapCellLeft() {
-      return utils.classNameMapCell(this.line.left, this.isHighlighted, this.isLoggedIn);
+      return utils.classNameMapCell({
+        line: this.line.left,
+        hll: this.isHighlighted || this.isCommented,
+        isLoggedIn: this.isLoggedIn,
+      });
     },
     classNameMapCellRight() {
-      return utils.classNameMapCell(this.line.right, this.isHighlighted, this.isLoggedIn);
+      return utils.classNameMapCell({
+        line: this.line.right,
+        hll: this.isHighlighted || this.isCommented,
+        isLoggedIn: this.isLoggedIn,
+      });
     },
     addCommentTooltipLeft() {
       return utils.addCommentTooltip(this.line.left);
@@ -131,6 +151,22 @@ export default {
         ? this.$options.THEIR_CHANGES
         : this.$options.OUR_CHANGES;
     },
+    onDragEnd() {
+      this.dragging = false;
+      if (!this.glFeatures.dragCommentSelection) return;
+
+      this.$emit('stopdragging');
+    },
+    onDragEnter(line, index) {
+      if (!this.glFeatures.dragCommentSelection) return;
+
+      this.$emit('enterdragging', { ...line, index });
+    },
+    onDragStart(line) {
+      this.$root.$emit('bv::hide::tooltip');
+      this.dragging = true;
+      this.$emit('startdragging', line);
+    },
   },
   OUR_CHANGES: 'HEAD//our changes',
   THEIR_CHANGES: 'origin//their changes',
@@ -143,7 +179,13 @@ export default {
 
 <template>
   <div :class="classNameMap" class="diff-grid-row diff-tr line_holder">
-    <div class="diff-grid-left left-side">
+    <div
+      data-testid="left-side"
+      class="diff-grid-left left-side"
+      @dragover.prevent
+      @dragenter="onDragEnter(line.left, index)"
+      @dragend="onDragEnd"
+    >
       <template v-if="line.left && line.left.type !== $options.CONFLICT_MARKER">
         <div
           :class="classNameMapCellLeft"
@@ -159,10 +201,13 @@ export default {
               :title="addCommentTooltipLeft"
             >
               <button
+                :draggable="glFeatures.dragCommentSelection"
                 type="button"
                 class="add-diff-note note-button js-add-diff-note-button qa-diff-comment"
+                :class="{ 'gl-cursor-grab': dragging }"
                 :disabled="line.left.commentsDisabled"
                 @click="handleCommentButton(line.left)"
+                @dragstart="onDragStart({ ...line.left, index })"
               >
                 <gl-icon :size="12" name="comment" />
               </button>
@@ -234,7 +279,14 @@ export default {
         ></div>
       </template>
     </div>
-    <div v-if="!inline" class="diff-grid-right right-side">
+    <div
+      v-if="!inline"
+      data-testid="right-side"
+      class="diff-grid-right right-side"
+      @dragover.prevent
+      @dragenter="onDragEnter(line.right, index)"
+      @dragend="onDragEnd"
+    >
       <template v-if="line.right">
         <div :class="classNameMapCellRight" class="diff-td diff-line-num new_line">
           <template v-if="line.right.type !== $options.CONFLICT_MARKER_THEIR">
@@ -246,10 +298,13 @@ export default {
               :title="addCommentTooltipRight"
             >
               <button
+                :draggable="glFeatures.dragCommentSelection"
                 type="button"
                 class="add-diff-note note-button js-add-diff-note-button qa-diff-comment"
+                :class="{ 'gl-cursor-grab': dragging }"
                 :disabled="line.right.commentsDisabled"
                 @click="handleCommentButton(line.right)"
+                @dragstart="onDragStart({ ...line.right, index })"
               >
                 <gl-icon :size="12" name="comment" />
               </button>
@@ -279,13 +334,21 @@ export default {
         <div
           v-gl-tooltip.hover
           :title="coverageState.text"
-          :class="[line.right.type, coverageState.class, { hll: isHighlighted }]"
+          :class="[line.right.type, coverageState.class, { hll: isHighlighted, hll: isCommented }]"
           class="diff-td line-coverage right-side"
         ></div>
         <div
           :id="line.right.line_code"
           :key="line.right.rich_text"
-          :class="[line.right.type, { hll: isHighlighted, parallel: !inline }]"
+          v-safe-html="line.right.rich_text"
+          :class="[
+            line.right.type,
+            {
+              hll: isHighlighted,
+              hll: isCommented,
+              parallel: !inline,
+            },
+          ]"
           class="diff-td line_content with-coverage right-side"
           @mousedown="handleParallelLineMouseDown"
         >

app/assets/javascripts/diffs/components/diff_row_utils.js

@@ -35,7 +35,7 @@ export const lineCode = (line) => {
   return line.line_code || line.left?.line_code || line.right?.line_code;
 };
 
-export const classNameMapCell = (line, hll, isLoggedIn, isHover) => {
+export const classNameMapCell = ({ line, hll, isLoggedIn, isHover }) => {
   if (!line) return [];
   const { type } = line;
 
@@ -54,7 +54,9 @@ export const addCommentTooltip = (line) => {
   let tooltip;
   if (!line) return tooltip;
 
-  tooltip = __('Add a comment to this line');
+  tooltip = gon.drag_comment_selection
+    ? __('Add a comment to this line or drag for multiple lines')
+    : __('Add a comment to this line');
   const brokenSymlinks = line.commentsDisabled;
 
   if (brokenSymlinks) {

app/assets/javascripts/diffs/components/diff_view.vue

 <script>
-import { mapGetters, mapState } from 'vuex';
+import { mapGetters, mapState, mapActions } from 'vuex';
 import draftCommentsMixin from '~/diffs/mixins/draft_comments';
 import DraftNote from '~/batch_comments/components/draft_note.vue';
 import DiffRow from './diff_row.vue';
@@ -35,6 +35,12 @@ export default {
       default: false,
     },
   },
+  data() {
+    return {
+      dragStart: null,
+      updatedLineRange: null,
+    };
+  },
   computed: {
     ...mapGetters('diffs', ['commitId']),
     ...mapState({
@@ -52,12 +58,39 @@ export default {
     },
   },
   methods: {
+    ...mapActions(['setSelectedCommentPosition']),
+    ...mapActions('diffs', ['showCommentForm']),
     showCommentLeft(line) {
       return !this.inline || line.left;
     },
     showCommentRight(line) {
       return !this.inline || (line.right && !line.left);
     },
+    onStartDragging(line) {
+      this.dragStart = line;
+    },
+    onDragOver(line) {
+      if (line.chunk !== this.dragStart.chunk) return;
+
+      let start = this.dragStart;
+      let end = line;
+
+      if (this.dragStart.index >= line.index) {
+        start = line;
+        end = this.dragStart;
+      }
+
+      this.updatedLineRange = { start, end };
+
+      this.setSelectedCommentPosition(this.updatedLineRange);
+    },
+    onStopDragging() {
+      this.showCommentForm({
+        lineCode: this.updatedLineRange?.end?.line_code,
+        fileHash: this.diffFile.file_hash,
+      });
+      this.dragStart = null;
+    },
   },
   userColorScheme: window.gon.user_color_scheme,
 };
@@ -94,6 +127,10 @@ export default {
         :is-bottom="index + 1 === diffLinesLength"
         :is-commented="index >= commentedLines.startLine && index <= commentedLines.endLine"
         :inline="inline"
+        :index="index"
+        @enterdragging="onDragOver"
+        @startdragging="onStartDragging"
+        @stopdragging="onStopDragging"
       />
       <div
         v-if="line.renderCommentRow"

app/assets/javascripts/diffs/components/inline_diff_table_row.vue

@@ -72,7 +72,12 @@ export default {
       return this.fileLineCoverage(this.filePath, this.line.new_line);
     },
     classNameMapCell() {
-      return classNameMapCell(this.line, this.isHighlighted, this.isLoggedIn, this.isHover);
+      return classNameMapCell({
+        line: this.line,
+        hll: this.isHighlighted,
+        isLoggedIn: this.isLoggedIn,
+        isHover: this.isHover,
+      });
     },
     addCommentTooltip() {
       return addCommentTooltip(this.line);

app/assets/javascripts/diffs/components/parallel_diff_table_row.vue

@@ -68,20 +68,20 @@ export default {
       return this.fileLineCoverage(this.filePath, this.line.right.new_line);
     },
     classNameMapCellLeft() {
-      return utils.classNameMapCell(
-        this.line.left,
-        this.isHighlighted,
-        this.isLoggedIn,
-        this.isLeftHover,
-      );
+      return utils.classNameMapCell({
+        line: this.line.left,
+        hll: this.isHighlighted,
+        isLoggedIn: this.isLoggedIn,
+        isHover: this.isLeftHover,
+      });
     },
     classNameMapCellRight() {
-      return utils.classNameMapCell(
-        this.line.right,
-        this.isHighlighted,
-        this.isLoggedIn,
-        this.isRightHover,
-      );
+      return utils.classNameMapCell({
+        line: this.line.right,
+        hll: this.isHighlighted,
+        isLoggedIn: this.isLoggedIn,
+        isHover: this.isRightHover,
+      });
     },
     addCommentTooltipLeft() {
       return utils.addCommentTooltip(this.line.left);

app/assets/javascripts/diffs/store/utils.js

@@ -55,8 +55,17 @@ export const parallelizeDiffLines = (diffLines, inline) => {
   let conflictStartIndex = -1;
   const lines = [];
 
+  // `chunk` is used for dragging to select diff lines
+  // we are restricting commenting to only lines that appear between
+  // "expansion rows". Here equal chunks are lines grouped together
+  // inbetween expansion rows.
+  let chunk = 0;
+
   for (let i = 0, diffLinesLength = diffLines.length, index = 0; i < diffLinesLength; i += 1) {
     const line = diffLines[i];
+    line.chunk = chunk;
+
+    if (isMeta(line)) chunk += 1;
 
     if (isRemoved(line) || isConflictOur(line) || inline) {
       lines.push({

app/assets/javascripts/notes/components/multiline_comment_form.vue

 <script>
-import { mapActions } from 'vuex';
+import { mapActions, mapState } from 'vuex';
 import { GlFormSelect, GlSprintf } from '@gitlab/ui';
 import { getSymbol, getLineClasses } from './multiline_comment_utils';
 
@@ -27,12 +27,13 @@ export default {
     };
   },
   computed: {
+    ...mapState({ selectedCommentPosition: ({ notes }) => notes.selectedCommentPosition }),
     lineNumber() {
       return this.commentLineOptions[this.commentLineOptions.length - 1].text;
     },
   },
   created() {
-    const line = this.lineRange?.start || this.line;
+    const line = this.selectedCommentPosition?.start || this.lineRange?.start || this.line;
 
     this.commentLineStart = {
       line_code: line.line_code,
@@ -40,6 +41,8 @@ export default {
       old_line: line.old_line,
       new_line: line.new_line,
     };
+
+    if (this.selectedCommentPosition) return;
     this.highlightSelection();
   },
   destroyed() {

app/assets/javascripts/notes/stores/modules/index.js

@@ -15,7 +15,7 @@ export default () => ({
     batchSuggestionsInfo: [],
     currentlyFetchingDiscussions: false,
     /**
-     * selectedCommentPosition & selectedCommentPosition structures are the same as `position.line_range`:
+     * selectedCommentPosition & selectedCommentPositionHover structures are the same as `position.line_range`:
      * {
      *  start: { line_code: string, new_line: number, old_line:number, type: string },
      *  end: { line_code: string, new_line: number, old_line:number, type: string },

app/assets/stylesheets/framework/variables.scss

@@ -516,9 +516,12 @@ $line-removed-dark-transparent: rgba(246, 53, 85, 0.2);
 $line-number-old: #f9d7dc;
 $line-number-new: #ddfbe6;
 $line-number-select: #fbf2da;
+$line-number-commented: #dae5fb;
 $line-target-blue: $blue-50;
 $line-select-yellow: #fcf8e7;
 $line-select-yellow-dark: #f0e2bd;
+$line-commented-blue: #e8effc;
+$line-commented-blue-dark: #bccef0;
 $dark-diff-match-bg: rgba($white, 0.3);
 $dark-diff-match-color: rgba($white, 0.1);
 $diff-image-info-color: #808080;

app/controllers/projects/merge_requests_controller.rb

@@ -33,6 +33,7 @@ class Projects::MergeRequestsController < Projects::MergeRequests::ApplicationCo
     push_frontend_feature_flag(:batch_suggestions, @project, default_enabled: true)
     push_frontend_feature_flag(:approvals_commented_by, @project, default_enabled: true)
     push_frontend_feature_flag(:merge_request_widget_graphql, @project)
+    push_frontend_feature_flag(:drag_comment_selection, @project, default_enabled: true)
     push_frontend_feature_flag(:unified_diff_components, @project, default_enabled: true)
     push_frontend_feature_flag(:default_merge_ref_for_diffs, @project)
     push_frontend_feature_flag(:core_security_mr_widget, @project, default_enabled: true)

config/feature_flags/development/drag_comment_selection.yml

+---
+name: drag_comment_selection
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/49875
+rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/293945
+milestone: '13.7'
+type: development
+group: group::source code
+default_enabled: true

locale/gitlab.pot

@@ -1627,6 +1627,9 @@ msgstr ""
 msgid "Add a comment to this line"
 msgstr ""
 
+msgid "Add a comment to this line or drag for multiple lines"
+msgstr ""
+
 msgid "Add a general comment to this %{noteableDisplayName}."
 msgstr ""
 

spec/frontend/diffs/components/diff_line_note_form_spec.js

@@ -11,14 +11,16 @@ describe('DiffLineNoteForm', () => {
   let diffLines;
   const getDiffFileMock = () => ({ ...diffFileMockData });
 
-  beforeEach(() => {
+  const createComponent = (args = {}) => {
     diffFile = getDiffFileMock();
     diffLines = diffFile.highlighted_diff_lines;
     const store = createStore();
     store.state.notes.userData.id = 1;
     store.state.notes.noteableData = noteableDataMock;
 
-    wrapper = shallowMount(DiffLineNoteForm, {
+    store.replaceState({ ...store.state, ...args.state });
+
+    return shallowMount(DiffLineNoteForm, {
       store,
       propsData: {
         diffFileHash: diffFile.file_hash,
@@ -27,9 +29,13 @@ describe('DiffLineNoteForm', () => {
         noteTargetLine: diffLines[0],
       },
     });
-  });
+  };
 
   describe('methods', () => {
+    beforeEach(() => {
+      wrapper = createComponent();
+    });
+
     describe('handleCancelCommentForm', () => {
       it('should ask for confirmation when shouldConfirm and isDirty passed as truthy', () => {
         jest.spyOn(window, 'confirm').mockReturnValue(false);
@@ -114,14 +120,39 @@ describe('DiffLineNoteForm', () => {
   describe('mounted', () => {
     it('should init autosave', () => {
       const key = 'autosave/Note/Issue/98//DiffNote//1c497fbb3a46b78edf04cc2a2fa33f67e3ffbe2a_1_1';
+      wrapper = createComponent();
 
       expect(wrapper.vm.autosave).toBeDefined();
       expect(wrapper.vm.autosave.key).toEqual(key);
     });
+
+    it('should set selectedCommentPosition', () => {
+      wrapper = createComponent();
+      let startLineCode = wrapper.vm.commentLineStart.line_code;
+      let lineCode = wrapper.vm.line.line_code;
+
+      expect(startLineCode).toEqual(lineCode);
+      wrapper.destroy();
+
+      const state = {
+        notes: {
+          selectedCommentPosition: {
+            start: {
+              line_code: 'test',
+            },
+          },
+        },
+      };
+      wrapper = createComponent({ state });
+      startLineCode = wrapper.vm.commentLineStart.line_code;
+      lineCode = state.notes.selectedCommentPosition.start.line_code;
+      expect(startLineCode).toEqual(lineCode);
+    });
   });
 
   describe('template', () => {
     it('should have note form', () => {
+      wrapper = createComponent();
       expect(wrapper.find(NoteForm).exists()).toBe(true);
     });
   });

spec/frontend/diffs/components/diff_row_spec.js

 import { shallowMount, createLocalVue } from '@vue/test-utils';
+import { getByTestId, fireEvent } from '@testing-library/dom';
 import Vuex from 'vuex';
 import diffsModule from '~/diffs/store/modules';
 import DiffRow from '~/diffs/components/diff_row.vue';
@@ -42,16 +43,16 @@ describe('DiffRow', () => {
       fileHash: 'abc',
       filePath: 'abc',
       line: {},
+      index: 0,
       ...props,
     };
-    return shallowMount(DiffRow, { propsData, localVue, store });
-  };
 
-  it('isHighlighted returns true if isCommented is true', () => {
-    const props = { isCommented: true };
-    const wrapper = createWrapper({ props });
-    expect(wrapper.vm.isHighlighted).toBe(true);
-  });
+    const provide = {
+      glFeatures: { dragCommentSelection: true },
+    };
+
+    return shallowMount(DiffRow, { propsData, localVue, store, provide });
+  };
 
   it('isHighlighted returns true given line.left', () => {
     const props = {
@@ -124,4 +125,36 @@ describe('DiffRow', () => {
     const lineNumber = testLines[0].right.new_line;
     expect(wrapper.find(`[data-linenumber="${lineNumber}"]`).exists()).toBe(true);
   });
+
+  describe('drag operations', () => {
+    let line;
+
+    beforeEach(() => {
+      line = { ...testLines[0] };
+    });
+
+    it.each`
+      side
+      ${'left'}
+      ${'right'}
+    `('emits `enterdragging` onDragEnter $side side', ({ side }) => {
+      const expectation = { ...line[side], index: 0 };
+      const wrapper = createWrapper({ props: { line } });
+      fireEvent.dragEnter(getByTestId(wrapper.element, `${side}-side`));
+
+      expect(wrapper.emitted().enterdragging).toBeTruthy();
+      expect(wrapper.emitted().enterdragging[0]).toEqual([expectation]);
+    });
+
+    it.each`
+      side
+      ${'left'}
+      ${'right'}
+    `('emits `stopdragging` onDrop $side side', ({ side }) => {
+      const wrapper = createWrapper({ props: { line } });
+      fireEvent.dragEnd(getByTestId(wrapper.element, `${side}-side`));
+
+      expect(wrapper.emitted().stopdragging).toBeTruthy();
+    });
+  });
 });

spec/frontend/diffs/components/diff_row_utils_spec.js

@@ -126,14 +126,14 @@ describe('lineCode', () => {
 
 describe('classNameMapCell', () => {
   it.each`
-    line               | hll      | loggedIn | hovered  | expectation
-    ${undefined}       | ${true}  | ${true}  | ${true}  | ${[]}
-    ${{ type: 'new' }} | ${false} | ${false} | ${false} | ${['new', { hll: false, 'is-over': false, new_line: true, old_line: false }]}
-    ${{ type: 'new' }} | ${true}  | ${true}  | ${false} | ${['new', { hll: true, 'is-over': false, new_line: true, old_line: false }]}
-    ${{ type: 'new' }} | ${true}  | ${false} | ${true}  | ${['new', { hll: true, 'is-over': false, new_line: true, old_line: false }]}
-    ${{ type: 'new' }} | ${true}  | ${true}  | ${true}  | ${['new', { hll: true, 'is-over': true, new_line: true, old_line: false }]}
-  `('should return $expectation', ({ line, hll, loggedIn, hovered, expectation }) => {
-    const classes = utils.classNameMapCell(line, hll, loggedIn, hovered);
+    line               | hll      | isLoggedIn | isHover  | expectation
+    ${undefined}       | ${true}  | ${true}    | ${true}  | ${[]}
+    ${{ type: 'new' }} | ${false} | ${false}   | ${false} | ${['new', { hll: false, 'is-over': false, new_line: true, old_line: false }]}
+    ${{ type: 'new' }} | ${true}  | ${true}    | ${false} | ${['new', { hll: true, 'is-over': false, new_line: true, old_line: false }]}
+    ${{ type: 'new' }} | ${true}  | ${false}   | ${true}  | ${['new', { hll: true, 'is-over': false, new_line: true, old_line: false }]}
+    ${{ type: 'new' }} | ${true}  | ${true}    | ${true}  | ${['new', { hll: true, 'is-over': true, new_line: true, old_line: false }]}
+  `('should return $expectation', ({ line, hll, isLoggedIn, isHover, expectation }) => {
+    const classes = utils.classNameMapCell({ line, hll, isLoggedIn, isHover });
     expect(classes).toEqual(expectation);
   });
 });

spec/frontend/diffs/components/diff_view_spec.js

-import { shallowMount, createLocalVue } from '@vue/test-utils';
+import Vue from 'vue';
+import { shallowMount } from '@vue/test-utils';
 import Vuex from 'vuex';
 import DiffView from '~/diffs/components/diff_view.vue';
-// import DraftNote from '~/batch_comments/components/draft_note.vue';
-// import DiffRow from '~/diffs/components/diff_row.vue';
-// import DiffCommentCell from '~/diffs/components/diff_comment_cell.vue';
-// import DiffExpansionCell from '~/diffs/components/diff_expansion_cell.vue';
 
 describe('DiffView', () => {
   const DiffExpansionCell = { template: `<div/>` };
   const DiffRow = { template: `<div/>` };
   const DiffCommentCell = { template: `<div/>` };
   const DraftNote = { template: `<div/>` };
+  const showCommentForm = jest.fn();
+  const setSelectedCommentPosition = jest.fn();
+  const getDiffRow = (wrapper) => wrapper.findComponent(DiffRow).vm;
+
   const createWrapper = (props) => {
-    const localVue = createLocalVue();
-    localVue.use(Vuex);
+    Vue.use(Vuex);
 
     const batchComments = {
       getters: {
@@ -26,8 +26,13 @@ describe('DiffView', () => {
       },
       namespaced: true,
     };
-    const diffs = { getters: { commitId: () => 'abc123' }, namespaced: true };
+    const diffs = {
+      actions: { showCommentForm },
+      getters: { commitId: () => 'abc123' },
+      namespaced: true,
+    };
     const notes = {
+      actions: { setSelectedCommentPosition },
       state: { selectedCommentPosition: null, selectedCommentPositionHover: null },
     };
 
@@ -41,7 +46,7 @@ describe('DiffView', () => {
       ...props,
     };
     const stubs = { DiffExpansionCell, DiffRow, DiffCommentCell, DraftNote };
-    return shallowMount(DiffView, { propsData, store, localVue, stubs });
+    return shallowMount(DiffView, { propsData, store, stubs });
   };
 
   it('renders a match line', () => {
@@ -74,4 +79,55 @@ describe('DiffView', () => {
     });
     expect(wrapper.find(DraftNote).exists()).toBe(true);
   });
+
+  describe('drag operations', () => {
+    it('sets `dragStart` onStartDragging', () => {
+      const wrapper = createWrapper({ diffLines: [{}] });
+
+      wrapper.findComponent(DiffRow).vm.$emit('startdragging', { test: true });
+      expect(wrapper.vm.dragStart).toEqual({ test: true });
+    });
+
+    it('does not call `setSelectedCommentPosition` on different chunks onDragOver', () => {
+      const wrapper = createWrapper({ diffLines: [{}] });
+      const diffRow = getDiffRow(wrapper);
+
+      diffRow.$emit('startdragging', { chunk: 0 });
+      diffRow.$emit('enterdragging', { chunk: 1 });
+
+      expect(setSelectedCommentPosition).not.toHaveBeenCalled();
+    });
+
+    it.each`
+      start | end  | expectation
+      ${1}  | ${2} | ${{ start: { index: 1 }, end: { index: 2 } }}
+      ${2}  | ${1} | ${{ start: { index: 1 }, end: { index: 2 } }}
+      ${1}  | ${1} | ${{ start: { index: 1 }, end: { index: 1 } }}
+    `(
+      'calls `setSelectedCommentPosition` with correct `updatedLineRange`',
+      ({ start, end, expectation }) => {
+        const wrapper = createWrapper({ diffLines: [{}] });
+        const diffRow = getDiffRow(wrapper);
+
+        diffRow.$emit('startdragging', { chunk: 1, index: start });
+        diffRow.$emit('enterdragging', { chunk: 1, index: end });
+
+        const arg = setSelectedCommentPosition.mock.calls[0][1];
+
+        expect(arg).toMatchObject(expectation);
+      },
+    );
+
+    it('sets `dragStart` to null onStopDragging', () => {
+      const wrapper = createWrapper({ diffLines: [{}] });
+      const diffRow = getDiffRow(wrapper);
+
+      diffRow.$emit('startdragging', { test: true });
+      expect(wrapper.vm.dragStart).toEqual({ test: true });
+
+      diffRow.$emit('stopdragging');
+      expect(wrapper.vm.dragStart).toBeNull();
+      expect(showCommentForm).toHaveBeenCalled();
+    });
+  });
 });

spec/frontend/diffs/store/utils_spec.js

@@ -1159,7 +1159,7 @@ describe('DiffsStoreUtils', () => {
     it('converts inline diff lines to parallel diff lines', () => {
       const file = getDiffFileMock();
 
-      expect(utils.parallelizeDiffLines(file[INLINE_DIFF_LINES_KEY])).toEqual(
+      expect(utils.parallelizeDiffLines(file[INLINE_DIFF_LINES_KEY])).toMatchObject(
         file.parallel_diff_lines,
       );
     });
@@ -1178,16 +1178,17 @@ describe('DiffsStoreUtils', () => {
         {
           left: null,
           right: {
+            chunk: 0,
             type: 'new',
           },
         },
         {
-          left: { type: 'conflict_marker_our' },
-          right: { type: 'conflict_marker_their' },
+          left: { chunk: 0, type: 'conflict_marker_our' },
+          right: { chunk: 0, type: 'conflict_marker_their' },
         },
         {
-          left: { type: 'conflict_our' },
-          right: { type: 'conflict_their' },
+          left: { chunk: 0, type: 'conflict_our' },
+          right: { chunk: 0, type: 'conflict_their' },
         },
       ]);
     });
@@ -1196,9 +1197,9 @@ describe('DiffsStoreUtils', () => {
       const file = getDiffFileMock();
       const files = utils.parallelizeDiffLines(file.highlighted_diff_lines, true);
 
-      expect(files[5].left).toEqual(file.parallel_diff_lines[5].left);
+      expect(files[5].left).toMatchObject(file.parallel_diff_lines[5].left);
       expect(files[5].right).toBeNull();
-      expect(files[6].left).toEqual(file.parallel_diff_lines[5].right);
+      expect(files[6].left).toMatchObject(file.parallel_diff_lines[5].right);
       expect(files[6].right).toBeNull();
     });
   });

spec/frontend/notes/components/multiline_comment_form_spec.js

+import Vue from 'vue';
+import Vuex from 'vuex';
+import { mount } from '@vue/test-utils';
+import { GlFormSelect } from '@gitlab/ui';
+import MultilineCommentForm from '~/notes/components/multiline_comment_form.vue';
+import notesModule from '~/notes/stores/modules';
+
+describe('MultilineCommentForm', () => {
+  Vue.use(Vuex);
+  const setSelectedCommentPosition = jest.fn();
+  const testLine = {
+    line_code: 'test',
+    type: 'test',
+    old_line: 'test',
+    new_line: 'test',
+  };
+
+  const createWrapper = (props = {}, state) => {
+    setSelectedCommentPosition.mockReset();
+
+    const store = new Vuex.Store({
+      modules: { notes: notesModule() },
+      actions: { setSelectedCommentPosition },
+    });
+    if (state) store.replaceState({ ...store.state, ...state });
+
+    const propsData = {
+      line: { ...testLine },
+      commentLineOptions: [{ text: '1' }],
+      ...props,
+    };
+    return mount(MultilineCommentForm, { propsData, store });
+  };
+
+  describe('created', () => {
+    it('sets commentLineStart to line', () => {
+      const line = { ...testLine };
+      const wrapper = createWrapper({ line });
+
+      expect(wrapper.vm.commentLineStart).toEqual(line);
+      expect(setSelectedCommentPosition).toHaveBeenCalled();
+    });
+
+    it('sets commentLineStart to lineRange', () => {
+      const lineRange = {
+        start: { ...testLine },
+      };
+      const wrapper = createWrapper({ lineRange });
+
+      expect(wrapper.vm.commentLineStart).toEqual(lineRange.start);
+      expect(setSelectedCommentPosition).toHaveBeenCalled();
+    });
+
+    it('sets commentLineStart to selectedCommentPosition', () => {
+      const notes = {
+        selectedCommentPosition: {
+          start: { ...testLine },
+        },
+      };
+      const wrapper = createWrapper({}, { notes });
+
+      expect(wrapper.vm.commentLineStart).toEqual(wrapper.vm.selectedCommentPosition.start);
+      expect(setSelectedCommentPosition).not.toHaveBeenCalled();
+    });
+  });
+
+  describe('destroyed', () => {
+    it('calls setSelectedCommentPosition', () => {
+      const wrapper = createWrapper();
+      wrapper.destroy();
+
+      // Once during created, once during destroyed
+      expect(setSelectedCommentPosition).toHaveBeenCalledTimes(2);
+    });
+  });
+
+  it('handles changing the start line', () => {
+    const line = { ...testLine };
+    const wrapper = createWrapper({ line });
+    const glSelect = wrapper.findComponent(GlFormSelect);
+
+    glSelect.vm.$emit('change', { ...testLine });
+
+    expect(wrapper.vm.commentLineStart).toEqual(line);
+    expect(wrapper.emitted('input')).toBeTruthy();
+    // Once during created, once during updateCommentLineStart
+    expect(setSelectedCommentPosition).toHaveBeenCalledTimes(2);
+  });
+});