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feat(eslint-plugin): add rule prefer-ts-expect-error (typescript-eslint#1705)
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‎packages/eslint-plugin/README.md

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@@ -152,6 +152,7 @@ Pro Tip: For larger codebases you may want to consider splitting our linting int
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| [`@typescript-eslint/prefer-reduce-type-parameter`](./docs/rules/prefer-reduce-type-parameter.md) | Prefer using type parameter when calling `Array#reduce` instead of casting | | :wrench: | :thought_balloon: |
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| [`@typescript-eslint/prefer-regexp-exec`](./docs/rules/prefer-regexp-exec.md) | Enforce that `RegExp#exec` is used instead of `String#match` if no global flag is provided | :heavy_check_mark: | | :thought_balloon: |
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| [`@typescript-eslint/prefer-string-starts-ends-with`](./docs/rules/prefer-string-starts-ends-with.md) | Enforce the use of `String#startsWith` and `String#endsWith` instead of other equivalent methods of checking substrings | :heavy_check_mark: | :wrench: | :thought_balloon: |
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| [`@typescript-eslint/prefer-ts-expect-error`](./docs/rules/prefer-ts-expect-error.md) | Recommends using `// @ts-expect-error` over `// @ts-ignore` | | :wrench: | |
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| [`@typescript-eslint/promise-function-async`](./docs/rules/promise-function-async.md) | Requires any function or method that returns a Promise to be marked async | | | :thought_balloon: |
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| [`@typescript-eslint/require-array-sort-compare`](./docs/rules/require-array-sort-compare.md) | Requires `Array#sort` calls to always provide a `compareFunction` | | | :thought_balloon: |
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| [`@typescript-eslint/restrict-plus-operands`](./docs/rules/restrict-plus-operands.md) | When adding two variables, operands must both be of type number or of type string | | | :thought_balloon: |

‎packages/eslint-plugin/docs/rules/prefer-ts-expect-error.md

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# Recommends using `// @ts-expect-error` over `// @ts-ignore` (`prefer-ts-expect-error`)
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TypeScript allows you to suppress all errors on a line by placing a single-line comment starting with `@ts-ignore` immediately before the erroring line.
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While powerful, there is no way to know if a `@ts-ignore` is actually suppressing an error without manually investigating what happens when the `@ts-ignore` is removed.
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This means its easy for `@ts-ignore`s to be forgotten about, and remain in code even after the error they were suppressing is fixed.
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This is dangerous, as if a new error arises on that line it'll be suppressed by the forgotten about `@ts-ignore`, and so be missed.
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To address this, TS3.9 ships with a new single-line comment directive: `// @ts-expect-error`.
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This directive operates in the same manner as `@ts-ignore`, but will error if the line it's meant to be suppressing doesn't actually contain an error, making it a lot safer.
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## Rule Details
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This rule looks for usages of `@ts-ignore`, and flags them to be replaced with `@ts-expect-error`.
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Examples of **incorrect** code for this rule:
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```ts
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// @ts-ignore
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const str: string = 1;
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const isOptionEnabled = (key: string): boolean => {
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// @ts-ignore: if key isn't in globalOptions it'll be undefined which is false
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return !!globalOptions[key];
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};
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```
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Examples of **correct** code for this rule:
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```ts
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// @ts-expect-error
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const str: string = 1;
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const isOptionEnabled = (key: string): boolean => {
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// @ts-expect-error: if key isn't in globalOptions it'll be undefined which is false
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return !!globalOptions[key];
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};
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```
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## When Not To Use It
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If you are not using TypeScript 3.9 (or greater), then you will not be able to use this rule, as the directive is not supported
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## Further Reading
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- [Original Implementing PR](https://github.com/microsoft/TypeScript/pull/36014)

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

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"@typescript-eslint/prefer-reduce-type-parameter": "error",
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"@typescript-eslint/prefer-regexp-exec": "error",
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"@typescript-eslint/prefer-string-starts-ends-with": "error",
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"@typescript-eslint/prefer-ts-expect-error": "error",
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"@typescript-eslint/promise-function-async": "error",
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"quotes": "off",
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"@typescript-eslint/quotes": "error",

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

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@@ -78,6 +78,7 @@ import preferReadonlyParameterTypes from './prefer-readonly-parameter-types';
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import preferReduceTypeParameter from './prefer-reduce-type-parameter';
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import preferRegexpExec from './prefer-regexp-exec';
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import preferStringStartsEndsWith from './prefer-string-starts-ends-with';
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import preferTsExpectError from './prefer-ts-expect-error';
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import promiseFunctionAsync from './promise-function-async';
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import quotes from './quotes';
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import requireArraySortCompare from './require-array-sort-compare';
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'prefer-reduce-type-parameter': preferReduceTypeParameter,
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'prefer-regexp-exec': preferRegexpExec,
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'prefer-string-starts-ends-with': preferStringStartsEndsWith,
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'prefer-ts-expect-error': preferTsExpectError,
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'promise-function-async': promiseFunctionAsync,
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quotes: quotes,
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'require-array-sort-compare': requireArraySortCompare,

‎packages/eslint-plugin/src/rules/prefer-ts-expect-error.ts

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import { AST_TOKEN_TYPES } from '@typescript-eslint/experimental-utils';
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import * as util from '../util';
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type MessageIds = 'preferExpectErrorComment';
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export default util.createRule<[], MessageIds>({
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name: 'prefer-ts-expect-error',
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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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'Recommends using `// @ts-expect-error` over `// @ts-ignore`',
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category: 'Best Practices',
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recommended: false,
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},
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fixable: 'code',
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messages: {
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preferExpectErrorComment:
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'Use "// @ts-expect-error" to ensure an error is actually being suppressed.',
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},
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schema: [],
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},
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defaultOptions: [],
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create(context) {
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const tsIgnoreRegExp = /^\/*\s*@ts-ignore/;
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const sourceCode = context.getSourceCode();
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return {
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Program(): void {
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const comments = sourceCode.getAllComments();
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comments.forEach(comment => {
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if (comment.type !== AST_TOKEN_TYPES.Line) {
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return;
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}
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if (tsIgnoreRegExp.test(comment.value)) {
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context.report({
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node: comment,
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messageId: 'preferExpectErrorComment',
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fix: fixer =>
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fixer.replaceText(
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comment,
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`//${comment.value.replace(
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'@ts-ignore',
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'@ts-expect-error',
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)}`,
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),
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});
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}
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});
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},
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};
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},
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});

‎packages/eslint-plugin/tests/rules/prefer-ts-expect-error.test.ts

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import rule from '../../src/rules/prefer-ts-expect-error';
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import { RuleTester } from '../RuleTester';
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const ruleTester = new RuleTester({
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parser: '@typescript-eslint/parser',
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});
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ruleTester.run('prefer-ts-expect-error', rule, {
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valid: [
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'// @ts-nocheck',
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'// @ts-check',
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'// just a comment containing @ts-ignore somewhere',
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'/* @ts-ignore */',
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'/** @ts-ignore */',
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`
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/*
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// @ts-ignore in a block
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*/
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`,
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'// @ts-expect-error',
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`
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if (false) {
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// @ts-expect-error: Unreachable code error
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console.log('hello');
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}
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`,
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],
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invalid: [
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{
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code: '// @ts-ignore',
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output: '// @ts-expect-error',
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errors: [
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{
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messageId: 'preferExpectErrorComment',
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line: 1,
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column: 1,
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},
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],
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},
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{
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code: '// @ts-ignore: Suppress next line',
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output: '// @ts-expect-error: Suppress next line',
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errors: [
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{
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messageId: 'preferExpectErrorComment',
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line: 1,
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column: 1,
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},
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],
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},
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{
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code: '/////@ts-ignore: Suppress next line',
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output: '/////@ts-expect-error: Suppress next line',
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errors: [
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{
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messageId: 'preferExpectErrorComment',
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line: 1,
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column: 1,
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},
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],
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},
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{
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code: `
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if (false) {
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// @ts-ignore: Unreachable code error
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console.log('hello');
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}
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`,
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output: `
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if (false) {
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// @ts-expect-error: Unreachable code error
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console.log('hello');
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}
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`,
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errors: [
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{
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messageId: 'preferExpectErrorComment',
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line: 3,
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column: 3,
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},
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],
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},
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],
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});

‎packages/typescript-estree/src/ts-estree/ts-estree.ts

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export type Comment = BlockComment | LineComment;
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export type Token =
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| BooleanToken
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| Comment
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| IdentifierToken
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| JSXIdentifierToken
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| JSXTextToken

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