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feat(eslint-plugin): add extension rule comma-dangle (typescript-eslint#2416)
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‎packages/eslint-plugin/README.md

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

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

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'@typescript-eslint/typedef': 'error',
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'@typescript-eslint/unbound-method': 'error',
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'@typescript-eslint/unified-signatures': 'error',
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'comma-dangle': 'off',
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'@typescript-eslint/comma-dangle': 'error',
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},
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};

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

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

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

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import banTypes from './ban-types';
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import braceStyle from './brace-style';
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import classLiteralPropertyStyle from './class-literal-property-style';
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import commaDangle from './comma-dangle';
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import commaSpacing from './comma-spacing';
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import confusingNonNullAssertionLikeNotEqual from './no-confusing-non-null-assertion';
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import consistentTypeAssertions from './consistent-type-assertions';
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'ban-types': banTypes,
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'brace-style': braceStyle,
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'class-literal-property-style': classLiteralPropertyStyle,
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'comma-dangle': commaDangle,
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'comma-spacing': commaSpacing,
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'consistent-type-assertions': consistentTypeAssertions,
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'consistent-type-definitions': consistentTypeDefinitions,

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