Resolve "Harmonize prettier and eslint configs"

.eslintrc.yml

----
 env:
   browser: true
   es6: true
 extends:
   - airbnb-base
+  - prettier
   - plugin:vue/recommended
 globals:
   __webpack_public_path__: true
@@ -19,34 +19,31 @@ plugins:
   - promise
 settings:
   html/html-extensions:
-  - ".html"
-  - ".html.raw"
+    - '.html'
+    - '.html.raw'
   import/resolver:
     webpack:
-      config: "./config/webpack.config.js"
+      config: './config/webpack.config.js'
 rules:
   filenames/match-regex:
     - error
-    - "^[a-z0-9_]+$"
+    - '^[a-z0-9_]+$'
   import/no-commonjs: error
-  no-multiple-empty-lines:
-    - error
-    - max: 1
   promise/catch-or-return: error
   no-param-reassign:
     - error
     - props: true
       ignorePropertyModificationsFor:
-        - "acc"         # for reduce accumulators
-        - "accumulator" # for reduce accumulators
-        - "el"          # for DOM elements
-        - "element"     # for DOM elements
-        - "state"       # for Vuex mutations
+        - 'acc' # for reduce accumulators
+        - 'accumulator' # for reduce accumulators
+        - 'el' # for DOM elements
+        - 'element' # for DOM elements
+        - 'state' # for Vuex mutations
   no-underscore-dangle:
     - error
     - allow:
-      - __
-      - _links
+        - __
+        - _links
   no-mixed-operators: off
   vue/html-self-closing:
     - error
@@ -60,31 +57,7 @@ rules:
     - error
     - properties: never
       ignoreDestructuring: true
-  ## Conflicting rules with prettier:
-  space-before-function-paren: off
-  curly: off
-  arrow-parens: off
-  function-paren-newline: off
-  object-curly-newline: off
-  padded-blocks: off
-  # Disabled for now, to make the eslint 3 -> eslint 5 update smoother
-  ## Indent rule. We are using the old for now: https://eslint.org/docs/user-guide/migrating-to-4.0.0#indent-rewrite
-  indent: off
-  indent-legacy:
-    - error
-    - 2
-    - SwitchCase: 1
-      VariableDeclarator: 1
-      outerIIFEBody: 1
-      FunctionDeclaration:
-        parameters: 1
-        body: 1
-      FunctionExpression:
-        parameters: 1
-        body: 1
   # Disabled for now, to make the airbnb-base 12.1.0 -> 13.1.0 update smoother
-  operator-linebreak: off
-  implicit-arrow-linebreak: off
   no-else-return:
     - error
     - allowElseIf: true

app/assets/javascripts/behaviors/markdown/copy_as_gfm.js

-/* eslint-disable object-shorthand, no-unused-vars, no-use-before-define, max-len, no-restricted-syntax, guard-for-in, no-continue */
+/* eslint-disable object-shorthand, no-unused-vars, no-use-before-define, no-restricted-syntax, guard-for-in, no-continue */
 import $ from 'jquery';
 import _ from 'underscore';

app/assets/javascripts/boards/components/board.js

-/* eslint-disable comma-dangle */
-
 import Sortable from 'sortablejs';
 import Vue from 'vue';
 import { n__ } from '~/locale';

app/assets/javascripts/boards/components/board_delete.js

-/* eslint-disable comma-dangle, no-alert */
+/* eslint-disable no-alert */
 import $ from 'jquery';
 import Vue from 'vue';

app/assets/javascripts/boards/components/board_sidebar.js

-/* eslint-disable comma-dangle, no-new */
+/* eslint-disable no-new */
 import $ from 'jquery';
 import Vue from 'vue';

app/assets/javascripts/boards/models/issue.js

-/* eslint-disable no-unused-vars, comma-dangle */
+/* eslint-disable no-unused-vars */
 /* global ListLabel */
 /* global ListMilestone */
 /* global ListAssignee */

app/assets/javascripts/boards/models/list.js

-/* eslint-disable no-underscore-dangle, class-methods-use-this, consistent-return, no-shadow, no-param-reassign, max-len */
+/* eslint-disable no-underscore-dangle, class-methods-use-this, consistent-return, no-shadow, no-param-reassign */
 /* global ListIssue */
 import { __ } from '~/locale';

app/assets/javascripts/boards/stores/boards_store.js

-/* eslint-disable comma-dangle, no-shadow */
+/* eslint-disable no-shadow */
 /* global List */
 import $ from 'jquery';

app/assets/javascripts/commit/image_file.js

-/* eslint-disable func-names, wrap-iife, no-var, prefer-arrow-callback, no-else-return, consistent-return, prefer-template, quotes, one-var, one-var-declaration-per-line, no-unused-vars, no-return-assign, comma-dangle, quote-props, no-unused-expressions, no-sequences, max-len */
+/* eslint-disable func-names, no-var, prefer-arrow-callback, no-else-return, consistent-return, prefer-template, one-var, no-unused-vars, no-return-assign, no-unused-expressions, no-sequences */
 import $ from 'jquery';

app/assets/javascripts/compare_autocomplete.js

-/* eslint-disable func-names, one-var, no-var, one-var-declaration-per-line, object-shorthand, no-else-return, max-len */
+/* eslint-disable func-names, one-var, no-var, object-shorthand, no-else-return */
 import $ from 'jquery';
 import { __ } from './locale';

app/assets/javascripts/diff_notes/components/comment_resolve_btn.js

-/* eslint-disable comma-dangle, object-shorthand, func-names, no-else-return, quotes, no-lonely-if, max-len */
+/* eslint-disable object-shorthand, func-names, no-else-return, no-lonely-if */
 /* global CommentsStore */
 import $ from 'jquery';

app/assets/javascripts/diff_notes/components/jump_to_discussion.js

-/* eslint-disable comma-dangle, object-shorthand, func-names, no-else-return, guard-for-in, no-restricted-syntax, no-lonely-if, no-continue, brace-style, max-len, quotes */
+/* eslint-disable object-shorthand, func-names, no-else-return, guard-for-in, no-restricted-syntax, no-lonely-if, no-continue */
 /* global CommentsStore */
 import $ from 'jquery';

app/assets/javascripts/diff_notes/components/resolve_count.js

-/* eslint-disable comma-dangle, object-shorthand, func-names */
+/* eslint-disable object-shorthand, func-names */
 /* global CommentsStore */
 import Vue from 'vue';

app/assets/javascripts/diff_notes/mixins/discussion.js

-/* eslint-disable object-shorthand, func-names, guard-for-in, no-restricted-syntax, comma-dangle, */
+/* eslint-disable object-shorthand, func-names, guard-for-in, no-restricted-syntax, */
 const DiscussionMixins = {
   computed: {

app/assets/javascripts/diff_notes/stores/comments.js

-/* eslint-disable object-shorthand, func-names, camelcase, no-restricted-syntax, guard-for-in, comma-dangle, max-len */
+/* eslint-disable object-shorthand, func-names, camelcase, no-restricted-syntax, guard-for-in */
 /* global DiscussionModel */
 import Vue from 'vue';

app/assets/javascripts/gl_dropdown.js

-/* eslint-disable func-names, no-underscore-dangle, no-var, one-var, one-var-declaration-per-line, max-len, vars-on-top, wrap-iife, no-unused-vars, no-shadow, no-cond-assign, prefer-arrow-callback, no-return-assign, no-else-return, camelcase, no-lonely-if, guard-for-in, no-restricted-syntax, consistent-return, prefer-template, no-param-reassign, no-loop-func */
+/* eslint-disable func-names, no-underscore-dangle, no-var, one-var, vars-on-top, no-unused-vars, no-shadow, no-cond-assign, prefer-arrow-callback, no-return-assign, no-else-return, camelcase, no-lonely-if, guard-for-in, no-restricted-syntax, consistent-return, prefer-template, no-param-reassign, no-loop-func */
 /* global fuzzaldrinPlus */
 import $ from 'jquery';

app/assets/javascripts/ide/stores/modules/commit/actions.js

@@ -30,9 +30,9 @@ export const setLastCommitMessage = ({ rootState, commit }, data) => {
   const currentProject = rootState.projects[rootState.currentProjectId];
   const commitStats = data.stats
     ? sprintf(__('with %{additions} additions, %{deletions} deletions.'), {
-        additions: data.stats.additions, // eslint-disable-line indent-legacy
-        deletions: data.stats.deletions, // eslint-disable-line indent-legacy
-      }) // eslint-disable-line indent-legacy
+        additions: data.stats.additions,
+        deletions: data.stats.deletions,
+      })
     : '';
   const commitMsg = sprintf(
     __('Your changes have been committed. Commit %{commitId} %{commitStats}'),

app/assets/javascripts/issuable_bulk_update_actions.js

-/* eslint-disable comma-dangle, quotes, consistent-return, func-names, array-callback-return, prefer-arrow-callback, max-len, no-unused-vars */
+/* eslint-disable consistent-return, func-names, array-callback-return, prefer-arrow-callback, no-unused-vars */
 import $ from 'jquery';
 import _ from 'underscore';

app/assets/javascripts/issue.js

-/* eslint-disable no-var, one-var, one-var-declaration-per-line, no-unused-vars, consistent-return, quotes, max-len */
+/* eslint-disable no-var, one-var, no-unused-vars, consistent-return */
 import $ from 'jquery';
 import axios from './lib/utils/axios_utils';

app/assets/javascripts/label_manager.js

-/* eslint-disable  class-methods-use-this, no-underscore-dangle, no-param-reassign, no-unused-vars, func-names, max-len */
+/* eslint-disable  class-methods-use-this, no-underscore-dangle, no-param-reassign, no-unused-vars, func-names */
 import $ from 'jquery';
 import Sortable from 'sortablejs';