feat(eslint-plugin): add extension rule comma-dangle (#2416)

packages/eslint-plugin/README.md

@@ -188,6 +188,7 @@ In these cases, we create what we call an extension rule; a rule within our plug
 | Name                                                                                            | Description                                                                          | :heavy_check_mark: | :wrench: | :thought_balloon: |
 | ----------------------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------ | ------------------ | -------- | ----------------- |
 | [`@typescript-eslint/brace-style`](./docs/rules/brace-style.md)                                 | Enforce consistent brace style for blocks                                            |                    | :wrench: |                   |
+| [`@typescript-eslint/comma-dangle`](./docs/rules/comma-dangle.md)                               | Require or disallow trailing comma                                                   |                    | :wrench: |                   |
 | [`@typescript-eslint/comma-spacing`](./docs/rules/comma-spacing.md)                             | Enforces consistent spacing before and after commas                                  |                    | :wrench: |                   |
 | [`@typescript-eslint/default-param-last`](./docs/rules/default-param-last.md)                   | Enforce default parameters to be last                                                |                    |          |                   |
 | [`@typescript-eslint/dot-notation`](./docs/rules/dot-notation.md)                               | enforce dot notation whenever possible                                               |                    | :wrench: | :thought_balloon: |

packages/eslint-plugin/docs/rules/comma-dangle.md

@@ -0,0 +1,34 @@
+# Require or disallow trailing comma (`comma-dangle`)
+
+## Rule Details
+
+This rule extends the base [`eslint/comma-dangle`](https://eslint.org/docs/rules/comma-dangle) rule.
+It adds support for TypeScript syntax.
+
+See the [ESLint documentation](https://eslint.org/docs/rules/comma-dangle) for more details on the `comma-dangle` rule.
+
+## Rule Changes
+
+```cjson
+{
+  // note you must disable the base rule as it can report incorrect errors
+  "comma-dangle": "off",
+  "@typescript-eslint/comma-dangle": ["error"]
+}
+```
+
+In addition to the options supported by the `comma-dangle` rule in ESLint core, the rule adds the following options:
+
+## Options
+
+This rule has a string option and an object option.
+
+- Object option:
+
+  - `"enums"` is for trailing comma in enum. (e.g. `enum Foo = {Bar,}`)
+  - `"generics"` is for trailing comma in generic. (e.g. `function foo<T,>() {}`)
+  - `"tuples"` is for trailing comma in tuple. (e.g. `type Foo = [string,]`)
+
+- [See the other options allowed](https://github.com/eslint/eslint/blob/master/docs/rules/comma-dangle.md#options)
+
+<sup>Taken with ❤️ [from ESLint core](https://github.com/eslint/eslint/blob/master/docs/rules/comma-dangle.md)</sup>

packages/eslint-plugin/src/configs/all.ts

@@ -139,5 +139,7 @@ export = {
     '@typescript-eslint/typedef': 'error',
     '@typescript-eslint/unbound-method': 'error',
     '@typescript-eslint/unified-signatures': 'error',
+    'comma-dangle': 'off',
+    '@typescript-eslint/comma-dangle': 'error',
   },
 };

packages/eslint-plugin/src/rules/comma-dangle.ts

@@ -0,0 +1,179 @@
+import * as util from '../util';
+import baseRule from 'eslint/lib/rules/comma-dangle';
+import {
+  TSESTree,
+  AST_NODE_TYPES,
+} from '@typescript-eslint/experimental-utils';
+
+export type Options = util.InferOptionsTypeFromRule<typeof baseRule>;
+export type MessageIds = util.InferMessageIdsTypeFromRule<typeof baseRule>;
+
+type Option = Options[0];
+type NormalizedOptions = Required<
+  Pick<Exclude<Option, string>, 'enums' | 'generics' | 'tuples'>
+>;
+
+const OPTION_VALUE_SCHEME = [
+  'always-multiline',
+  'always',
+  'never',
+  'only-multiline',
+];
+
+const DEFAULT_OPTION_VALUE = 'never';
+
+function normalizeOptions(options: Option): NormalizedOptions {
+  if (typeof options === 'string') {
+    return {
+      enums: options,
+      generics: options,
+      tuples: options,
+    };
+  }
+  return {
+    enums: options.enums ?? DEFAULT_OPTION_VALUE,
+    generics: options.generics ?? DEFAULT_OPTION_VALUE,
+    tuples: options.tuples ?? DEFAULT_OPTION_VALUE,
+  };
+}
+
+export default util.createRule<Options, MessageIds>({
+  name: 'comma-dangle',
+  meta: {
+    type: 'layout',
+    docs: {
+      description: 'Require or disallow trailing comma',
+      category: 'Stylistic Issues',
+      recommended: false,
+      extendsBaseRule: true,
+    },
+    schema: {
+      definitions: {
+        value: {
+          enum: OPTION_VALUE_SCHEME,
+        },
+        valueWithIgnore: {
+          enum: [...OPTION_VALUE_SCHEME, 'ignore'],
+        },
+      },
+      type: 'array',
+      items: [
+        {
+          oneOf: [
+            {
+              $ref: '#/definitions/value',
+            },
+            {
+              type: 'object',
+              properties: {
+                arrays: { $ref: '#/definitions/valueWithIgnore' },
+                objects: { $ref: '#/definitions/valueWithIgnore' },
+                imports: { $ref: '#/definitions/valueWithIgnore' },
+                exports: { $ref: '#/definitions/valueWithIgnore' },
+                functions: { $ref: '#/definitions/valueWithIgnore' },
+                enums: { $ref: '#/definitions/valueWithIgnore' },
+                generics: { $ref: '#/definitions/valueWithIgnore' },
+                tuples: { $ref: '#/definitions/valueWithIgnore' },
+              },
+              additionalProperties: false,
+            },
+          ],
+        },
+      ],
+    },
+    fixable: 'code',
+    messages: baseRule.meta.messages,
+  },
+  defaultOptions: ['never'],
+  create(context, [options]) {
+    const rules = baseRule.create(context);
+    const sourceCode = context.getSourceCode();
+    const normalizedOptions = normalizeOptions(options);
+
+    const predicate = {
+      always: forceComma,
+      'always-multiline': forceCommaIfMultiline,
+      'only-multiline': allowCommaIfMultiline,
+      never: forbidComma,
+      ignore: (): void => {},
+    };
+
+    function last(nodes: TSESTree.Node[]): TSESTree.Node | null {
+      return nodes[nodes.length - 1] ?? null;
+    }
+
+    function getLastItem(node: TSESTree.Node): TSESTree.Node | null {
+      switch (node.type) {
+        case AST_NODE_TYPES.TSEnumDeclaration:
+          return last(node.members);
+        case AST_NODE_TYPES.TSTypeParameterDeclaration:
+          return last(node.params);
+        case AST_NODE_TYPES.TSTupleType:
+          return last(node.elementTypes);
+        default:
+          return null;
+      }
+    }
+
+    function getTrailingToken(node: TSESTree.Node): TSESTree.Token | null {
+      const last = getLastItem(node);
+      const trailing = last && sourceCode.getTokenAfter(last);
+      return trailing;
+    }
+
+    function isMultiline(node: TSESTree.Node): boolean {
+      const last = getLastItem(node);
+      const lastToken = sourceCode.getLastToken(node);
+      return last?.loc.end.line !== lastToken?.loc.end.line;
+    }
+
+    function forbidComma(node: TSESTree.Node): void {
+      const last = getLastItem(node);
+      const trailing = getTrailingToken(node);
+      if (last && trailing && util.isCommaToken(trailing)) {
+        context.report({
+          node,
+          messageId: 'unexpected',
+          fix(fixer) {
+            return fixer.remove(trailing);
+          },
+        });
+      }
+    }
+
+    function forceComma(node: TSESTree.Node): void {
+      const last = getLastItem(node);
+      const trailing = getTrailingToken(node);
+      if (last && trailing && !util.isCommaToken(trailing)) {
+        context.report({
+          node,
+          messageId: 'missing',
+          fix(fixer) {
+            return fixer.insertTextAfter(last, ',');
+          },
+        });
+      }
+    }
+
+    function allowCommaIfMultiline(node: TSESTree.Node): void {
+      if (!isMultiline(node)) {
+        forbidComma(node);
+      }
+    }
+
+    function forceCommaIfMultiline(node: TSESTree.Node): void {
+      if (isMultiline(node)) {
+        forceComma(node);
+      } else {
+        forbidComma(node);
+      }
+    }
+
+    return {
+      ...rules,
+      TSEnumDeclaration: predicate[normalizedOptions.enums],
+      TSTypeParameterDeclaration: predicate[normalizedOptions.generics],
+      TSTupleType: predicate[normalizedOptions.tuples],
+    };
+  },
+});

packages/eslint-plugin/src/rules/index.ts

@@ -6,6 +6,7 @@ import banTslintComment from './ban-tslint-comment';
 import banTypes from './ban-types';
 import braceStyle from './brace-style';
 import classLiteralPropertyStyle from './class-literal-property-style';
+import commaDangle from './comma-dangle';
 import commaSpacing from './comma-spacing';
 import confusingNonNullAssertionLikeNotEqual from './no-confusing-non-null-assertion';
 import consistentTypeAssertions from './consistent-type-assertions';
@@ -114,6 +115,7 @@ export default {
   'ban-types': banTypes,
   'brace-style': braceStyle,
   'class-literal-property-style': classLiteralPropertyStyle,
+  'comma-dangle': commaDangle,
   'comma-spacing': commaSpacing,
   'consistent-type-assertions': consistentTypeAssertions,
   'consistent-type-definitions': consistentTypeDefinitions,