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feat(eslint-plugin): [class-methods-use-this] add extension rule (typescript-eslint#6457)
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‎packages/eslint-plugin/TSLINT_RULE_ALTERNATIVES.md

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@@ -185,7 +185,7 @@ It lists all TSLint rules along side rules from the ESLint ecosystem that are th
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| [`one-line`] | 🌟 | [`brace-style`][brace-style] or [Prettier] |
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| [`one-variable-per-declaration`] | 🌟 | [`one-var`][one-var] |
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| [`ordered-imports`] | 🌓 | [`import/order`] |
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| [`prefer-function-over-method`] | 🌟 | [`class-methods-use-this`][class-methods-use-this] |
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| [`prefer-function-over-method`] | 🌟 | [`@typescript-eslint/class-methods-use-this`] |
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| [`prefer-method-signature`] | ✅ | [`@typescript-eslint/method-signature-style`] |
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| [`prefer-switch`] | 🛑 | N/A |
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| [`prefer-template`] | 🌟 | [`prefer-template`][prefer-template] |
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[object-shorthand]: https://eslint.org/docs/rules/object-shorthand
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[brace-style]: https://eslint.org/docs/rules/brace-style
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[one-var]: https://eslint.org/docs/rules/one-var
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[class-methods-use-this]: https://eslint.org/docs/rules/class-methods-use-this
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[prefer-template]: https://eslint.org/docs/rules/prefer-template
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[quotes]: https://eslint.org/docs/rules/quotes
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[semi]: https://eslint.org/docs/rules/semi
@@ -598,6 +597,7 @@ Relevant plugins: [`chai-expect-keywords`](https://github.com/gavinaiken/eslint-
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[`@typescript-eslint/await-thenable`]: https://typescript-eslint.io/rules/await-thenable
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[`@typescript-eslint/ban-types`]: https://typescript-eslint.io/rules/ban-types
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[`@typescript-eslint/ban-ts-comment`]: https://typescript-eslint.io/rules/ban-ts-comment
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[`@typescript-eslint/class-methods-use-this`]: https://typescript-eslint.io/rules/class-methods-use-this
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[`@typescript-eslint/consistent-type-assertions`]: https://typescript-eslint.io/rules/consistent-type-assertions
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[`@typescript-eslint/consistent-type-definitions`]: https://typescript-eslint.io/rules/consistent-type-definitions
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[`@typescript-eslint/explicit-member-accessibility`]: https://typescript-eslint.io/rules/explicit-member-accessibility

‎packages/eslint-plugin/docs/rules/TEMPLATE.md

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---
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description: '<Description from rule metadata here>'
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---
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> 🛑 This file is source code, not the primary documentation location! 🛑
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>
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> See **https://typescript-eslint.io/rules/your-rule-name** for documentation.
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> See **https://typescript-eslint.io/rules/RULE_NAME_REPLACEME** for documentation.
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## Examples
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‎packages/eslint-plugin/docs/rules/class-methods-use-this.md

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---
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description: 'Enforce that class methods utilize `this`.'
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---
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> 🛑 This file is source code, not the primary documentation location! 🛑
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>
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> See **https://typescript-eslint.io/rules/class-methods-use-this** for documentation.
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## Examples
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This rule extends the base [`eslint/class-methods-use-this`](https://eslint.org/docs/rules/class-methods-use-this) rule.
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It adds support for ignoring `override` methods or methods on classes that implement an interface.
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## Options
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This rule adds the following options:
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```ts
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interface Options extends BaseClassMethodsUseThisOptions {
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ignoreOverrideMethods?: boolean;
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ignoreClassesThatImplementAnInterface?: boolean;
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}
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const defaultOptions: Options = {
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...baseClassMethodsUseThisOptions,
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ignoreOverrideMethods: false,
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ignoreClassesThatImplementAnInterface: false,
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};
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```
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### `ignoreOverrideMethods`
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Makes the rule to ignores any class member explicitly marked with `override`.
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Example of a correct code when `ignoreOverrideMethods` is set to `true`:
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```ts
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class X {
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override method() {}
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override property = () => {};
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}
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```
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### `ignoreClassesThatImplementAnInterface`
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Makes the rule ignore all class members that are defined within a class that `implements` a type.
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It's important to note that this option does not only apply to members defined in the interface as that would require type information.
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Example of a correct code when `ignoreClassesThatImplementAnInterface` is set to `true`:
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```ts
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class X implements Y {
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method() {}
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property = () => {};
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}
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```

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

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'brace-style': 'off',
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'@typescript-eslint/brace-style': 'error',
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'@typescript-eslint/class-literal-property-style': 'error',
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'class-methods-use-this': 'off',
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'@typescript-eslint/class-methods-use-this': 'error',
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'comma-dangle': 'off',
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'@typescript-eslint/comma-dangle': 'error',
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'comma-spacing': 'off',

‎packages/eslint-plugin/src/rules/class-methods-use-this.ts

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import type { TSESTree } from '@typescript-eslint/utils';
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import { AST_NODE_TYPES } from '@typescript-eslint/utils';
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import * as util from '../util';
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type Options = [
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{
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exceptMethods?: string[];
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enforceForClassFields?: boolean;
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ignoreOverrideMethods?: boolean;
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ignoreClassesThatImplementAnInterface?: boolean;
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},
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];
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type MessageIds = 'missingThis';
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export default util.createRule<Options, MessageIds>({
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name: 'class-methods-use-this',
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meta: {
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type: 'suggestion',
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docs: {
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description: 'Enforce that class methods utilize `this`',
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extendsBaseRule: true,
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requiresTypeChecking: false,
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},
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fixable: 'code',
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hasSuggestions: false,
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schema: [
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{
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type: 'object',
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properties: {
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exceptMethods: {
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type: 'array',
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description:
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'Allows specified method names to be ignored with this rule',
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items: {
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type: 'string',
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},
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},
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enforceForClassFields: {
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type: 'boolean',
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description:
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'Enforces that functions used as instance field initializers utilize `this`',
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default: true,
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},
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ignoreOverrideMethods: {
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type: 'boolean',
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description: 'Ingore members marked with the `override` modifier',
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},
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ignoreClassesThatImplementAnInterface: {
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type: 'boolean',
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description:
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'Ignore classes that specifically implement some interface',
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},
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},
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additionalProperties: false,
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},
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],
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messages: {
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missingThis: "Expected 'this' to be used by class {{name}}.",
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},
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},
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defaultOptions: [
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{
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enforceForClassFields: true,
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exceptMethods: [],
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ignoreClassesThatImplementAnInterface: false,
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ignoreOverrideMethods: false,
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},
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],
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create(
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context,
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[
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{
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enforceForClassFields,
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exceptMethods: exceptMethodsRaw,
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ignoreClassesThatImplementAnInterface,
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ignoreOverrideMethods,
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},
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],
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) {
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const exceptMethods = new Set(exceptMethodsRaw);
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type Stack =
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| {
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member: null;
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class: null;
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parent: Stack | undefined;
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usesThis: boolean;
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}
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| {
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member: TSESTree.MethodDefinition | TSESTree.PropertyDefinition;
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class: TSESTree.ClassDeclaration | TSESTree.ClassExpression;
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parent: Stack | undefined;
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usesThis: boolean;
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};
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let stack: Stack | undefined;
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const sourceCode = context.getSourceCode();
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function pushContext(
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member?: TSESTree.MethodDefinition | TSESTree.PropertyDefinition,
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): void {
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if (member?.parent.type === AST_NODE_TYPES.ClassBody) {
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stack = {
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member,
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class: member.parent.parent as
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| TSESTree.ClassDeclaration
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| TSESTree.ClassExpression,
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usesThis: false,
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parent: stack,
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};
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} else {
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stack = {
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member: null,
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class: null,
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usesThis: false,
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parent: stack,
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};
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}
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}
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function enterFunction(
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node: TSESTree.ArrowFunctionExpression | TSESTree.FunctionExpression,
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): void {
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if (
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node.parent.type === AST_NODE_TYPES.MethodDefinition ||
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node.parent.type === AST_NODE_TYPES.PropertyDefinition
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) {
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pushContext(node.parent);
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} else {
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pushContext();
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}
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}
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/**
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* Pop `this` used flag from the stack.
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*/
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function popContext(): Stack | undefined {
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const oldStack = stack;
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stack = stack?.parent;
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return oldStack;
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}
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/**
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* Check if the node is an instance method not excluded by config
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*/
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function isIncludedInstanceMethod(
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node: NonNullable<Stack['member']>,
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): node is NonNullable<Stack['member']> {
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if (
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node.static ||
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(node.type === AST_NODE_TYPES.MethodDefinition &&
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node.kind === 'constructor') ||
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(node.type === AST_NODE_TYPES.PropertyDefinition &&
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!enforceForClassFields)
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) {
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return false;
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}
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if (node.computed || exceptMethods.size === 0) {
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return true;
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}
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const hashIfNeeded =
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node.key.type === AST_NODE_TYPES.PrivateIdentifier ? '#' : '';
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const name =
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node.key.type === AST_NODE_TYPES.Literal
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? util.getStaticStringValue(node.key)
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: node.key.name || '';
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return !exceptMethods.has(hashIfNeeded + (name ?? ''));
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}
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/**
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* Checks if we are leaving a function that is a method, and reports if 'this' has not been used.
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* Static methods and the constructor are exempt.
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* Then pops the context off the stack.
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*/
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function exitFunction(
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node: TSESTree.ArrowFunctionExpression | TSESTree.FunctionExpression,
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): void {
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const stackContext = popContext();
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if (
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stackContext?.member == null ||
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stackContext.class == null ||
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stackContext.usesThis ||
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(ignoreOverrideMethods && stackContext.member.override) ||
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(ignoreClassesThatImplementAnInterface &&
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stackContext.class.implements != null)
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) {
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return;
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}
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if (isIncludedInstanceMethod(stackContext.member)) {
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context.report({
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node,
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loc: util.getFunctionHeadLoc(node, sourceCode),
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messageId: 'missingThis',
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data: {
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name: util.getFunctionNameWithKind(node),
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},
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});
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}
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}
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return {
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// function declarations have their own `this` context
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FunctionDeclaration(): void {
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pushContext();
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},
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'FunctionDeclaration:exit'(): void {
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popContext();
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},
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FunctionExpression(node): void {
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enterFunction(node);
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},
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'FunctionExpression:exit'(node): void {
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exitFunction(node);
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},
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...(enforceForClassFields
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? {
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'PropertyDefinition > ArrowFunctionExpression.value'(
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node: TSESTree.ArrowFunctionExpression,
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): void {
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enterFunction(node);
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},
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'PropertyDefinition > ArrowFunctionExpression.value:exit'(
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node: TSESTree.ArrowFunctionExpression,
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): void {
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exitFunction(node);
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},
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}
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: {}),
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/*
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* Class field value are implicit functions.
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*/
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'PropertyDefinition > *.key:exit'(): void {
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pushContext();
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},
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'PropertyDefinition:exit'(): void {
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popContext();
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},
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/*
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* Class static blocks are implicit functions. They aren't required to use `this`,
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* but we have to push context so that it captures any use of `this` in the static block
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* separately from enclosing contexts, because static blocks have their own `this` and it
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* shouldn't count as used `this` in enclosing contexts.
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*/
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StaticBlock(): void {
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pushContext();
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},
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'StaticBlock:exit'(): void {
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popContext();
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},
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'ThisExpression, Super'(): void {
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if (stack) {
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stack.usesThis = true;
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}
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},
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};
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},
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});

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

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@@ -7,6 +7,7 @@ import banTypes from './ban-types';
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import blockSpacing from './block-spacing';
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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 classMethodsUseThis from './class-methods-use-this';
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import commaDangle from './comma-dangle';
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import commaSpacing from './comma-spacing';
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import consistentGenericConstructors from './consistent-generic-constructors';
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'block-spacing': blockSpacing,
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'brace-style': braceStyle,
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'class-literal-property-style': classLiteralPropertyStyle,
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'class-methods-use-this': classMethodsUseThis,
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'comma-dangle': commaDangle,
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'comma-spacing': commaSpacing,
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'consistent-generic-constructors': consistentGenericConstructors,

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