feat: support ESLint v9

.eslintrc.js

@@ -92,7 +92,7 @@ module.exports = {
       },
     },
     {
-      files: ['src/**/*', 'dangerfile.ts'],
+      files: ['src/**/*', 'dangerfile.ts', './jest.config.ts'],
       parserOptions: {
         sourceType: 'module',
       },

.github/workflows/nodejs.yml

@@ -72,7 +72,14 @@ jobs:
       fail-fast: false
       matrix:
         node-version: [14.x, 16.x, 18.x, 19.x, 20.x, 21.x]
-        eslint-version: [7, 8]
+        eslint-version: [7, 8, 9]
+        exclude:
+          # eslint@9 doesn't support node@16
+          - node-version: 16.x
+            eslint-version: 9
+          # eslint@9 doesn't support node@14
+          - node-version: 14.x
+            eslint-version: 9
     runs-on: ubuntu-latest
 
     steps:
@@ -92,11 +99,11 @@ jobs:
           yarn add --dev eslint@${{ matrix.eslint-version }}
       - name: run tests
         # only collect coverage on eslint versions that support dynamic import
-        run: yarn test --coverage ${{ matrix.eslint-version >= 8 }}
+        run: yarn test --coverage ${{ matrix.eslint-version == 8 }}
         env:
           CI: true
       - uses: codecov/codecov-action@v3
-        if: ${{ matrix.eslint-version >= 8 }}
+        if: ${{ matrix.eslint-version == 8 }}
   test-ubuntu:
     uses: ./.github/workflows/test.yml
     needs: prepare-yarn-cache-ubuntu

jest.config.ts

@@ -0,0 +1,44 @@
+import { version as eslintVersion } from 'eslint/package.json';
+import type { Config } from 'jest';
+import * as semver from 'semver';
+
+const config = {
+  clearMocks: true,
+  restoreMocks: true,
+  resetMocks: true,
+
+  coverageThreshold: {
+    global: {
+      branches: 100,
+      functions: 100,
+      lines: 100,
+      statements: 100,
+    },
+  },
+
+  projects: [
+    {
+      displayName: 'test',
+      testPathIgnorePatterns: [
+        '<rootDir>/lib/.*',
+        '<rootDir>/src/rules/__tests__/test-utils.ts',
+      ],
+      coveragePathIgnorePatterns: ['/node_modules/'],
+    },
+    {
+      displayName: 'lint',
+      runner: 'jest-runner-eslint',
+      testMatch: ['<rootDir>/**/*.{js,ts}'],
+      testPathIgnorePatterns: ['<rootDir>/lib/.*'],
+      coveragePathIgnorePatterns: ['/node_modules/'],
+    },
+  ],
+} satisfies Config;
+
+if (semver.major(eslintVersion) >= 9) {
+  config.projects = config.projects.filter(
+    ({ displayName }) => displayName !== 'lint',
+  );
+}
+
+export default config;

package.json

@@ -69,35 +69,6 @@
       "@semantic-release/github"
     ]
   },
-  "jest": {
-    "coverageThreshold": {
-      "global": {
-        "branches": 100,
-        "functions": 100,
-        "lines": 100,
-        "statements": 100
-      }
-    },
-    "projects": [
-      {
-        "displayName": "test",
-        "testPathIgnorePatterns": [
-          "<rootDir>/lib/.*",
-          "<rootDir>/src/rules/__tests__/test-utils.ts"
-        ]
-      },
-      {
-        "displayName": "lint",
-        "runner": "jest-runner-eslint",
-        "testMatch": [
-          "<rootDir>/**/*.{js,ts}"
-        ],
-        "testPathIgnorePatterns": [
-          "<rootDir>/lib/.*"
-        ]
-      }
-    ]
-  },
   "resolutions": {
     "@typescript-eslint/experimental-utils": "^5.0.0"
   },
@@ -123,7 +94,7 @@
     "babel-jest": "^29.0.0",
     "babel-plugin-replace-ts-export-assignment": "^0.0.2",
     "dedent": "^1.0.0",
-    "eslint": "^6.0.0 || ^7.0.0 || ^8.0.0",
+    "eslint": "^6.0.0 || ^7.0.0 || ^8.0.0 || ^9.0.0",
     "eslint-config-prettier": "^9.0.0",
     "eslint-doc-generator": "^1.0.0",
     "eslint-plugin-eslint-comments": "^3.1.2",
@@ -143,12 +114,12 @@
     "prettier": "^3.0.0",
     "rimraf": "^5.0.0",
     "semantic-release": "^23.0.0",
-    "semver": "^7.0.0",
+    "semver": "^7.6.0",
     "ts-node": "^10.9.1",
     "typescript": "^5.0.0"
   },
   "peerDependencies": {
-    "eslint": "^7.0.0 || ^8.0.0"
+    "eslint": "^7.0.0 || ^8.0.0 || ^9.0.0"
   },
   "packageManager": "yarn@3.8.1",
   "engines": {

src/rules/__tests__/prefer-to-be-array.test.ts

@@ -1,8 +1,8 @@
-import { TSESLint } from '@typescript-eslint/utils';
+import type { TSESLint } from '@typescript-eslint/utils';
 import rule, { type MessageIds, type Options } from '../prefer-to-be-array';
-import { espreeParser } from './test-utils';
+import { FlatCompatRuleTester as RuleTester, espreeParser } from './test-utils';
 
-const ruleTester = new TSESLint.RuleTester({
+const ruleTester = new RuleTester({
   parser: espreeParser,
   parserOptions: {
     ecmaVersion: 2017,

src/rules/__tests__/prefer-to-be-false.test.ts

@@ -1,7 +1,7 @@
-import { TSESLint } from '@typescript-eslint/utils';
 import rule from '../prefer-to-be-false';
+import { FlatCompatRuleTester as RuleTester } from './test-utils';
 
-const ruleTester = new TSESLint.RuleTester();
+const ruleTester = new RuleTester();
 
 ruleTester.run('prefer-to-be-false', rule, {
   valid: [
@@ -58,7 +58,7 @@ ruleTester.run('prefer-to-be-false', rule, {
   ],
 });
 
-new TSESLint.RuleTester({
+new RuleTester({
   parser: require.resolve('@typescript-eslint/parser'),
 }).run('prefer-to-be-false: typescript edition', rule, {
   valid: [

src/rules/__tests__/prefer-to-be-object.test.ts

@@ -1,7 +1,8 @@
-import { TSESLint } from '@typescript-eslint/utils';
+import type { TSESLint } from '@typescript-eslint/utils';
 import rule, { type MessageIds, type Options } from '../prefer-to-be-object';
+import { FlatCompatRuleTester as RuleTester } from './test-utils';
 
-const ruleTester = new TSESLint.RuleTester();
+const ruleTester = new RuleTester();
 
 // makes ts happy about the dynamic test generation
 const messageId = 'preferToBeObject' as const;

src/rules/__tests__/prefer-to-be-true.test.ts

@@ -1,7 +1,7 @@
-import { TSESLint } from '@typescript-eslint/utils';
 import rule from '../prefer-to-be-true';
+import { FlatCompatRuleTester as RuleTester } from './test-utils';
 
-const ruleTester = new TSESLint.RuleTester();
+const ruleTester = new RuleTester();
 
 ruleTester.run('prefer-to-be-true', rule, {
   valid: [
@@ -58,7 +58,7 @@ ruleTester.run('prefer-to-be-true', rule, {
   ],
 });
 
-new TSESLint.RuleTester({
+new RuleTester({
   parser: require.resolve('@typescript-eslint/parser'),
 }).run('prefer-to-be-true: typescript edition', rule, {
   valid: [

src/rules/__tests__/prefer-to-have-been-called-once.test.ts

@@ -1,7 +1,7 @@
-import { TSESLint } from '@typescript-eslint/utils';
 import rule from '../prefer-to-have-been-called-once';
+import { FlatCompatRuleTester as RuleTester } from './test-utils';
 
-const ruleTester = new TSESLint.RuleTester();
+const ruleTester = new RuleTester();
 
 ruleTester.run('prefer-to-have-been-called-once', rule, {
   valid: [
@@ -38,7 +38,7 @@ ruleTester.run('prefer-to-have-been-called-once', rule, {
   ],
 });
 
-new TSESLint.RuleTester({
+new RuleTester({
   parser: require.resolve('@typescript-eslint/parser'),
 }).run('prefer-to-have-been-called-once: typescript edition', rule, {
   valid: [

src/rules/__tests__/test-utils.ts

@@ -1,6 +1,163 @@
 import { createRequire } from 'module';
+import { TSESLint } from '@typescript-eslint/utils';
+import { version as eslintVersion } from 'eslint/package.json';
+import * as semver from 'semver';
 
 const require = createRequire(__filename);
 const eslintRequire = createRequire(require.resolve('eslint'));
 
 export const espreeParser = eslintRequire.resolve('espree');
+
+export const usingFlatConfig = semver.major(eslintVersion) >= 9;
+
+export class FlatCompatRuleTester extends TSESLint.RuleTester {
+  public constructor(testerConfig?: TSESLint.RuleTesterConfig) {
+    super(FlatCompatRuleTester._flatCompat(testerConfig));
+  }
+
+  public override run<
+    TMessageIds extends string,
+    TOptions extends Readonly<unknown[]>,
+  >(
+    ruleName: string,
+    rule: TSESLint.RuleModule<TMessageIds, TOptions>,
+    tests: TSESLint.RunTests<TMessageIds, TOptions>,
+  ) {
+    super.run(ruleName, rule, {
+      valid: tests.valid.map(t => FlatCompatRuleTester._flatCompat(t)),
+      invalid: tests.invalid.map(t => FlatCompatRuleTester._flatCompat(t)),
+    });
+  }
+
+  /* istanbul ignore next */
+  private static _flatCompat<
+    T extends
+      | undefined
+      | RuleTesterConfig
+      | string
+      | TSESLint.ValidTestCase<unknown[]>
+      | TSESLint.InvalidTestCase<string, unknown[]>,
+  >(config: T): T {
+    if (!config || !usingFlatConfig || typeof config === 'string') {
+      return config;
+    }
+
+    const obj: FlatConfig.Config & {
+      languageOptions: FlatConfig.LanguageOptions & {
+        parserOptions: FlatConfig.ParserOptions;
+      };
+    } = {
+      languageOptions: { parserOptions: {} },
+    };
+
+    for (const [key, value] of Object.entries(config)) {
+      if (key === 'parser') {
+        obj.languageOptions.parser = require(value);
+
+        continue;
+      }
+
+      if (key === 'parserOptions') {
+        for (const [option, val] of Object.entries(value)) {
+          if (option === 'ecmaVersion' || option === 'sourceType') {
+            // @ts-expect-error: TS thinks the value could the opposite type of whatever option is
+            obj.languageOptions[option] = val as FlatConfig.LanguageOptions[
+              | 'ecmaVersion'
+              | 'sourceType'];
+
+            continue;
+          }
+
+          obj.languageOptions.parserOptions[option] = val;
+        }
+
+        continue;
+      }
+
+      obj[key as keyof typeof obj] = value;
+    }
+
+    return obj as unknown as T;
+  }
+}
+
+type RuleTesterConfig = TSESLint.RuleTesterConfig | FlatConfig.Config;
+
+export declare namespace FlatConfig {
+  type EcmaVersion = TSESLint.EcmaVersion;
+  type ParserOptions = TSESLint.ParserOptions;
+  type SourceType = TSESLint.SourceType | 'commonjs';
+  interface LanguageOptions {
+    /**
+     * The version of ECMAScript to support.
+     * May be any year (i.e., `2022`) or version (i.e., `5`).
+     * Set to `"latest"` for the most recent supported version.
+     * @default "latest"
+     */
+    ecmaVersion?: EcmaVersion;
+    /**
+     * An object specifying additional objects that should be added to the global scope during linting.
+     */
+    globals?: unknown;
+    /**
+     * An object containing a `parse()` method or a `parseForESLint()` method.
+     * @default
+     * ```
+     * // https://github.com/eslint/espree
+     * require('espree')
+     * ```
+     */
+    parser?: unknown;
+    /**
+     * An object specifying additional options that are passed directly to the parser.
+     * The available options are parser-dependent.
+     */
+    parserOptions?: ParserOptions;
+    /**
+     * The type of JavaScript source code.
+     * Possible values are `"script"` for traditional script files, `"module"` for ECMAScript modules (ESM), and `"commonjs"` for CommonJS files.
+     * @default
+     * ```
+     * // for `.js` and `.mjs` files
+     * "module"
+     * // for `.cjs` files
+     * "commonjs"
+     * ```
+     */
+    sourceType?: SourceType;
+  }
+  interface Config {
+    /**
+     * An array of glob patterns indicating the files that the configuration object should apply to.
+     * If not specified, the configuration object applies to all files matched by any other configuration object.
+     */
+    files?: string[];
+    /**
+     * An array of glob patterns indicating the files that the configuration object should not apply to.
+     * If not specified, the configuration object applies to all files matched by files.
+     */
+    ignores?: string[];
+    /**
+     * An object containing settings related to how JavaScript is configured for linting.
+     */
+    languageOptions?: LanguageOptions;
+    /**
+     * An object containing settings related to the linting process.
+     */
+    linterOptions?: unknown;
+    /**
+     * An object containing a name-value mapping of plugin names to plugin objects.
+     * When `files` is specified, these plugins are only available to the matching files.
+     */
+    plugins?: unknown;
+    /**
+     * An object containing the configured rules.
+     * When `files` or `ignores` are specified, these rule configurations are only available to the matching files.
+     */
+    rules?: unknown;
+    /**
+     * An object containing name-value pairs of information that should be available to all rules.
+     */
+    settings?: unknown;
+  }
+}