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feat(eslint-plugin): create no-invalid-void-type rule (typescript-eslint#1847)
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‎packages/eslint-plugin/README.md

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@@ -119,6 +119,7 @@ Pro Tip: For larger codebases you may want to consider splitting our linting int
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| [`@typescript-eslint/no-for-in-array`](./docs/rules/no-for-in-array.md) | Disallow iterating over an array with a for-in loop | :heavy_check_mark: | | :thought_balloon: |
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| [`@typescript-eslint/no-implied-eval`](./docs/rules/no-implied-eval.md) | Disallow the use of `eval()`-like methods | | | :thought_balloon: |
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| [`@typescript-eslint/no-inferrable-types`](./docs/rules/no-inferrable-types.md) | Disallows explicit type declarations for variables or parameters initialized to a number, string, or boolean | :heavy_check_mark: | :wrench: | |
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| [`@typescript-eslint/no-invalid-void-type`](./docs/rules/no-invalid-void-type.md) | Disallows usage of `void` type outside of generic or return types | | | |
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| [`@typescript-eslint/no-misused-new`](./docs/rules/no-misused-new.md) | Enforce valid definition of `new` and `constructor` | :heavy_check_mark: | | |
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| [`@typescript-eslint/no-misused-promises`](./docs/rules/no-misused-promises.md) | Avoid using promises in places not designed to handle them | :heavy_check_mark: | | :thought_balloon: |
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| [`@typescript-eslint/no-namespace`](./docs/rules/no-namespace.md) | Disallow the use of custom TypeScript modules and namespaces | :heavy_check_mark: | | |

‎packages/eslint-plugin/ROADMAP.md

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@@ -18,7 +18,7 @@ It lists all TSLint rules along side rules from the ESLint ecosystem that are th
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| [`adjacent-overload-signatures`] | ✅ | [`@typescript-eslint/adjacent-overload-signatures`] |
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| [`ban-ts-ignore`] | ✅ | [`@typescript-eslint/ban-ts-ignore`] |
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| [`ban-types`] | 🌓 | [`@typescript-eslint/ban-types`]<sup>[1]</sup> |
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| [`invalid-void`] | 🛑 | N/A |
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| [`invalid-void`] | ✅ | [`@typescript-eslint/no-invalid-void-type`] |
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| [`member-access`] | ✅ | [`@typescript-eslint/explicit-member-accessibility`] |
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| [`member-ordering`] | ✅ | [`@typescript-eslint/member-ordering`] |
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| [`no-any`] | ✅ | [`@typescript-eslint/no-explicit-any`] |
@@ -623,6 +623,7 @@ Relevant plugins: [`chai-expect-keywords`](https://github.com/gavinaiken/eslint-
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[`@typescript-eslint/restrict-plus-operands`]: https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/restrict-plus-operands.md
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[`@typescript-eslint/strict-boolean-expressions`]: https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/strict-boolean-expressions.md
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[`@typescript-eslint/indent`]: https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/indent.md
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[`@typescript-eslint/no-invalid-void-type`]: https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/no-invalid-void-type.md
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[`@typescript-eslint/no-require-imports`]: https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/no-require-imports.md
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[`@typescript-eslint/array-type`]: https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/array-type.md
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[`@typescript-eslint/class-name-casing`]: https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/class-name-casing.md

‎packages/eslint-plugin/docs/rules/no-invalid-void-type.md

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# Disallows usage of `void` type outside of generic or return types (`no-invalid-void-type`)
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Disallows usage of `void` type outside of return types or generic type arguments.
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If `void` is used as return type, it shouldn’t be a part of intersection/union type.
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## Rationale
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The `void` type means “nothing” or that a function does not return any value,
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in contrast with implicit `undefined` type which means that a function returns a value `undefined`.
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So “nothing” cannot be mixed with any other types. If you need this - use the `undefined` type instead.
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## Rule Details
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This rule aims to ensure that the `void` type is only used in valid places.
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The following patterns are considered warnings:
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```ts
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type PossibleValues = string | number | void;
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type MorePossibleValues = string | ((number & any) | (string | void));
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function logSomething(thing: void) {}
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function printArg<T = void>(arg: T) {}
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logAndReturn<void>(undefined);
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interface Interface {
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lambda: () => void;
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prop: void;
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}
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class MyClass {
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private readonly propName: void;
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}
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```
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The following patterns are not considered warnings:
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```ts
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type NoOp = () => void;
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function noop(): void {}
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let trulyUndefined = void 0;
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async function promiseMeSomething(): Promise<void> {}
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```
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### Options
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```ts
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interface Options {
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allowInGenericTypeArguments?: boolean | string[];
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}
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const defaultOptions: Options = {
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allowInGenericTypeArguments: true,
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};
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```
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#### `allowInGenericTypeArguments`
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This option lets you control if `void` can be used as a valid value for generic type parameters.
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Alternatively, you can provide an array of strings which whitelist which types may accept `void` as a generic type parameter.
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This option is `true` by default.
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The following patterns are considered warnings with `{ allowInGenericTypeArguments: false }`:
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```ts
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logAndReturn<void>(undefined);
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let voidPromise: Promise<void> = new Promise<void>(() => {});
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let voidMap: Map<string, void> = new Map<string, void>();
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```
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The following patterns are considered warnings with `{ allowInGenericTypeArguments: ['Ex.Mx.Tx'] }`:
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```ts
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logAndReturn<void>(undefined);
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type NotAllowedVoid1 = Mx.Tx<void>;
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type NotAllowedVoid2 = Tx<void>;
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type NotAllowedVoid3 = Promise<void>;
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```
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The following patterns are not considered warnings with `{ allowInGenericTypeArguments: ['Ex.Mx.Tx'] }`:
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```ts
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type AllowedVoid = Ex.MX.Tx<void>;
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```
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## When Not To Use It
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If you don't care about if `void` is used with other types,
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or in invalid places, then you don't need this rule.
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## Compatibility
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- TSLint: [invalid-void](https://palantir.github.io/tslint/rules/invalid-void/)

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

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"@typescript-eslint/no-for-in-array": "error",
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"@typescript-eslint/no-implied-eval": "error",
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"@typescript-eslint/no-inferrable-types": "error",
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"@typescript-eslint/no-invalid-void-type": "error",
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"no-magic-numbers": "off",
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"@typescript-eslint/no-magic-numbers": "error",
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"@typescript-eslint/no-misused-new": "error",

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

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@@ -40,6 +40,7 @@ import noFloatingPromises from './no-floating-promises';
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import noForInArray from './no-for-in-array';
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import noImpliedEval from './no-implied-eval';
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import noInferrableTypes from './no-inferrable-types';
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import noInvalidVoidType from './no-invalid-void-type';
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import noMagicNumbers from './no-magic-numbers';
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import noMisusedNew from './no-misused-new';
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import noMisusedPromises from './no-misused-promises';
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'no-for-in-array': noForInArray,
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'no-implied-eval': noImpliedEval,
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'no-inferrable-types': noInferrableTypes,
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'no-invalid-void-type': noInvalidVoidType,
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'no-magic-numbers': noMagicNumbers,
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'no-misused-new': noMisusedNew,
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'no-misused-promises': noMisusedPromises,

‎packages/eslint-plugin/src/rules/no-invalid-void-type.ts

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import {
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AST_NODE_TYPES,
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TSESTree,
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} from '@typescript-eslint/experimental-utils';
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import * as util from '../util';
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interface Options {
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allowInGenericTypeArguments: boolean | string[];
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}
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type MessageIds =
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| 'invalidVoidForGeneric'
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| 'invalidVoidNotReturnOrGeneric'
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| 'invalidVoidNotReturn';
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export default util.createRule<[Options], MessageIds>({
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name: 'no-invalid-void-type',
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meta: {
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type: 'problem',
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docs: {
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description:
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'Disallows usage of `void` type outside of generic or return types',
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category: 'Best Practices',
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recommended: false,
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},
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messages: {
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invalidVoidForGeneric:
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'{{ generic }} may not have void as a type variable',
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invalidVoidNotReturnOrGeneric:
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'void is only valid as a return type or generic type variable',
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invalidVoidNotReturn: 'void is only valid as a return type',
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},
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schema: [
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{
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type: 'object',
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properties: {
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allowInGenericTypeArguments: {
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oneOf: [
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{ type: 'boolean' },
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{
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type: 'array',
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items: { type: 'string' },
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minLength: 1,
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},
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],
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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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},
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defaultOptions: [{ allowInGenericTypeArguments: true }],
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create(context, [{ allowInGenericTypeArguments }]) {
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const validParents: AST_NODE_TYPES[] = [
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AST_NODE_TYPES.TSTypeAnnotation, //
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];
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const invalidGrandParents: AST_NODE_TYPES[] = [
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AST_NODE_TYPES.TSPropertySignature,
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AST_NODE_TYPES.CallExpression,
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AST_NODE_TYPES.ClassProperty,
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AST_NODE_TYPES.Identifier,
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];
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if (allowInGenericTypeArguments === true) {
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validParents.push(AST_NODE_TYPES.TSTypeParameterInstantiation);
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}
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return {
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TSVoidKeyword(node: TSESTree.TSVoidKeyword): void {
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/* istanbul ignore next */
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if (!node.parent?.parent) {
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return;
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}
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if (
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validParents.includes(node.parent.type) &&
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!invalidGrandParents.includes(node.parent.parent.type)
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) {
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return;
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}
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if (
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node.parent.type === AST_NODE_TYPES.TSTypeParameterInstantiation &&
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node.parent.parent.type === AST_NODE_TYPES.TSTypeReference &&
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Array.isArray(allowInGenericTypeArguments)
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) {
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const sourceCode = context.getSourceCode();
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const fullyQualifiedName = sourceCode
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.getText(node.parent.parent.typeName)
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.replace(/ /gu, '');
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if (
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!allowInGenericTypeArguments
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.map(s => s.replace(/ /gu, ''))
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.includes(fullyQualifiedName)
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) {
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context.report({
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messageId: 'invalidVoidForGeneric',
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data: { generic: fullyQualifiedName },
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node,
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});
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}
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return;
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}
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context.report({
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messageId: allowInGenericTypeArguments
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? 'invalidVoidNotReturnOrGeneric'
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: 'invalidVoidNotReturn',
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node,
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});
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},
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};
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},
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});

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