chore: run eslint with type information on CI

.github/workflows/nodejs.yml

@@ -54,6 +54,8 @@ jobs:
         run: yarn typecheck:examples
       - name: typecheck tests
         run: yarn typecheck:tests
+      - name: run ESLint with type info
+        run: yarn lint-ts-files
 
   lint:
     name: Lint

e2e/__tests__/__snapshots__/moduleNameMapper.test.ts.snap

@@ -41,7 +41,7 @@ exports[`moduleNameMapper wrong array configuration 1`] = `
       12 | module.exports = () => 'test';
       13 |
 
-      at createNoMappedModuleFoundError (../../packages/jest-resolve/build/resolver.js:896:17)
+      at createNoMappedModuleFoundError (../../packages/jest-resolve/build/resolver.js:891:17)
       at Object.require (index.js:10:1)
       at Object.require (__tests__/index.js:10:20)"
 `;
@@ -71,7 +71,7 @@ exports[`moduleNameMapper wrong configuration 1`] = `
       12 | module.exports = () => 'test';
       13 |
 
-      at createNoMappedModuleFoundError (../../packages/jest-resolve/build/resolver.js:896:17)
+      at createNoMappedModuleFoundError (../../packages/jest-resolve/build/resolver.js:891:17)
       at Object.require (index.js:10:1)
       at Object.require (__tests__/index.js:10:20)"
 `;

package.json

@@ -103,6 +103,7 @@
     "lint:prettier-script": "prettier . \"!**/*.{js,jsx,cjs,mjs,ts,tsx}\" --cache",
     "lint:prettier": "yarn lint:prettier-script --write",
     "lint:prettier:ci": "yarn lint:prettier-script --check",
+    "lint-ts-files": "node scripts/lintTs.mjs",
     "remove-examples": "node ./scripts/remove-examples.mjs",
     "test-ci-partial": "yarn test-ci-partial:parallel -i",
     "test-ci-partial:parallel": "yarn jest --color --config jest.config.ci.mjs",

packages/babel-jest/src/__tests__/getCacheKey.test.ts

@@ -52,7 +52,8 @@ describe('getCacheKey', () => {
       readFileSync: () => 'new this file',
     }));
 
-    const {createTransformer}: typeof import('../index') = require('../index');
+    const {createTransformer} =
+      require('../index') as typeof import('../index');
 
     const newCacheKey = createTransformer().getCacheKey!(
       sourceText,
@@ -65,7 +66,7 @@ describe('getCacheKey', () => {
 
   test('if `babelOptions.options` value is changing', () => {
     jest.doMock('../loadBabelConfig', () => {
-      const babel: typeof import('@babel/core') = require('@babel/core');
+      const babel = require('@babel/core') as typeof import('@babel/core');
 
       return {
         loadPartialConfig: (options: BabelTransformOptions) => ({
@@ -75,7 +76,8 @@ describe('getCacheKey', () => {
       };
     });
 
-    const {createTransformer}: typeof import('../index') = require('../index');
+    const {createTransformer} =
+      require('../index') as typeof import('../index');
 
     const newCacheKey = createTransformer().getCacheKey!(
       sourceText,
@@ -117,7 +119,7 @@ describe('getCacheKey', () => {
 
   test('if `babelOptions.config` value is changing', () => {
     jest.doMock('../loadBabelConfig', () => {
-      const babel: typeof import('@babel/core') = require('@babel/core');
+      const babel = require('@babel/core') as typeof import('@babel/core');
 
       return {
         loadPartialConfig: (options: BabelTransformOptions) => ({
@@ -127,7 +129,8 @@ describe('getCacheKey', () => {
       };
     });
 
-    const {createTransformer}: typeof import('../index') = require('../index');
+    const {createTransformer} =
+      require('../index') as typeof import('../index');
 
     const newCacheKey = createTransformer().getCacheKey!(
       sourceText,
@@ -140,7 +143,7 @@ describe('getCacheKey', () => {
 
   test('if `babelOptions.babelrc` value is changing', () => {
     jest.doMock('../loadBabelConfig', () => {
-      const babel: typeof import('@babel/core') = require('@babel/core');
+      const babel = require('@babel/core') as typeof import('@babel/core');
 
       return {
         loadPartialConfig: (options: BabelTransformOptions) => ({
@@ -150,7 +153,8 @@ describe('getCacheKey', () => {
       };
     });
 
-    const {createTransformer}: typeof import('../index') = require('../index');
+    const {createTransformer} =
+      require('../index') as typeof import('../index');
 
     const newCacheKey = createTransformer().getCacheKey!(
       sourceText,

packages/babel-jest/src/__tests__/index.ts

@@ -13,14 +13,17 @@ import {makeProjectConfig} from '@jest/test-utils';
 import type {TransformOptions} from '@jest/transform';
 import babelJest, {createTransformer} from '../index';
 import {loadPartialConfig} from '../loadBabelConfig';
+
 jest.mock('../loadBabelConfig', () => {
   const actual =
     jest.requireActual<typeof import('@babel/core')>('@babel/core');
 
   return {
-    loadPartialConfig: jest.fn((...args) => actual.loadPartialConfig(...args)),
-    loadPartialConfigAsync: jest.fn((...args) =>
-      actual.loadPartialConfigAsync(...args),
+    loadPartialConfig: jest.fn<typeof actual.loadPartialConfig>((...args) =>
+      actual.loadPartialConfig(...args),
+    ),
+    loadPartialConfigAsync: jest.fn<typeof actual.loadPartialConfigAsync>(
+      (...args) => actual.loadPartialConfigAsync(...args),
     ),
   };
 });
@@ -69,7 +72,7 @@ test('Returns source string with inline maps when no transformOptions is passed'
 });
 
 test('Returns source string with inline maps when no transformOptions is passed async', async () => {
-  const result: any = await defaultBabelJestTransformer.processAsync!(
+  const result = await defaultBabelJestTransformer.processAsync!(
     sourceString,
     'dummy_path.js',
     {
@@ -86,8 +89,18 @@ test('Returns source string with inline maps when no transformOptions is passed
   expect(result.map).toBeDefined();
   expect(result.code).toMatch('//# sourceMappingURL');
   expect(result.code).toMatch('customMultiply');
-  expect(result.map!.sources).toEqual(['dummy_path.js']);
-  expect(JSON.stringify(result.map!.sourcesContent)).toMatch('customMultiply');
+
+  const {map} = result;
+
+  expect(map).toBeTruthy();
+  expect(typeof map).not.toBe('string');
+
+  if (map == null || typeof map === 'string') {
+    throw new Error('dead code');
+  }
+
+  expect(map.sources).toEqual(['dummy_path.js']);
+  expect(JSON.stringify(map.sourcesContent)).toMatch('customMultiply');
 });
 
 describe('caller option correctly merges from defaults and options', () => {

packages/babel-jest/src/index.ts

@@ -51,7 +51,7 @@ function addIstanbulInstrumentation(
     const copiedBabelOptions: TransformOptions = {...babelOptions};
     copiedBabelOptions.auxiliaryCommentBefore = ' istanbul ignore next ';
     // Copied from jest-runtime transform.js
-    copiedBabelOptions.plugins = (copiedBabelOptions.plugins || []).concat([
+    copiedBabelOptions.plugins = (copiedBabelOptions.plugins ?? []).concat([
       [
         babelIstanbulPlugin,
         {
@@ -76,7 +76,7 @@ function getCacheKeyFromConfig(
 ): string {
   const {config, configString, instrument} = transformOptions;
 
-  const configPath = [babelOptions.config || '', babelOptions.babelrc || ''];
+  const configPath = [babelOptions.config ?? '', babelOptions.babelrc ?? ''];
 
   return createHash('sha256')
     .update(THIS_FILE)
@@ -93,9 +93,9 @@ function getCacheKeyFromConfig(
     .update('\0', 'utf8')
     .update(instrument ? 'instrument' : '')
     .update('\0', 'utf8')
-    .update(process.env.NODE_ENV || '')
+    .update(process.env.NODE_ENV ?? '')
     .update('\0', 'utf8')
-    .update(process.env.BABEL_ENV || '')
+    .update(process.env.BABEL_ENV ?? '')
     .update('\0', 'utf8')
     .update(process.version)
     .digest('hex')

packages/babel-plugin-jest-hoist/src/index.ts

@@ -114,10 +114,10 @@ const IDVisitor = {
   ],
 };
 
-const FUNCTIONS: Record<
+const FUNCTIONS = Object.create(null) as Record<
   string,
   <T extends Node>(args: Array<NodePath<T>>) => boolean
-> = Object.create(null);
+>;
 
 FUNCTIONS.mock = args => {
   if (args.length === 1) {
@@ -142,7 +142,7 @@ FUNCTIONS.mock = args => {
       let scope = id.scope;
 
       while (scope !== parentScope) {
-        if (scope.bindings[name]) {
+        if (scope.bindings[name] != null) {
           found = true;
           break;
         }

packages/diff-sequences/src/__tests__/index.property.test.ts

@@ -27,7 +27,7 @@ const findCommonItems = (a: Array<string>, b: Array<string>): Array<string> => {
 const extractCount = (data: Array<string>): Map<string, number> => {
   const countPerChar = new Map<string, number>();
   for (const item of data) {
-    const currentCount = countPerChar.get(item) || 0;
+    const currentCount = countPerChar.get(item) ?? 0;
     countPerChar.set(item, currentCount + 1);
   }
   return countPerChar;
@@ -93,7 +93,7 @@ it('should have at most the same number of each character as its inputs', () =>
       const commonCount = extractCount(commonItems);
       const aCount = extractCount(a);
       for (const [item, count] of commonCount) {
-        const countOfItemInA = aCount.get(item) || 0;
+        const countOfItemInA = aCount.get(item) ?? 0;
         expect(countOfItemInA).toBeGreaterThanOrEqual(count);
       }
     }),

packages/diff-sequences/src/__tests__/index.test.ts

@@ -15,7 +15,8 @@ describe('invalid arg', () => {
   describe('length', () => {
     test('is not a number', () => {
       expect(() => {
-        diff('0' as any, 0, isCommon, foundSubsequence);
+        // @ts-expect-error: Testing runtime errors here
+        diff('0', 0, isCommon, foundSubsequence);
       }).toThrow(/aLength/);
     });
     test('Infinity is not a safe integer', () => {
@@ -49,12 +50,14 @@ describe('invalid arg', () => {
   describe('callback', () => {
     test('null is not a function', () => {
       expect(() => {
-        diff(0, 0, null as any, foundSubsequence);
+        // @ts-expect-error: Testing runtime errors here
+        diff(0, 0, null, foundSubsequence);
       }).toThrow(/isCommon/);
     });
     test('undefined is not a function', () => {
       expect(() => {
-        diff(0, 0, isCommon, undefined as any);
+        // @ts-expect-error: Testing runtime errors here
+        diff(0, 0, isCommon, undefined);
       }).toThrow(/foundSubsequence/);
     });
   });

packages/expect-utils/src/jasmineUtils.ts

@@ -211,9 +211,7 @@ function keys(obj: object, hasKey: (obj: object, key: string) => boolean) {
   }
   return keys.concat(
     (Object.getOwnPropertySymbols(obj) as Array<any>).filter(
-      symbol =>
-        (Object.getOwnPropertyDescriptor(obj, symbol) as PropertyDescriptor)
-          .enumerable,
+      symbol => Object.getOwnPropertyDescriptor(obj, symbol)!.enumerable,
     ),
   );
 }

packages/expect/src/__tests__/toThrowMatchers.test.ts

@@ -458,9 +458,9 @@ matchers.forEach(toThrow => {
           err = new Err('async apple');
         }
         if (resolve) {
-          return await Promise.resolve(err || 'apple');
+          return Promise.resolve(err || 'apple');
         } else {
-          return await Promise.reject(err || 'apple');
+          return Promise.reject(err || 'apple');
         }
       };
 

packages/expect/src/asymmetricMatchers.ts

@@ -296,7 +296,7 @@ class StringMatching extends AsymmetricMatcher<RegExp> {
 }
 
 class CloseTo extends AsymmetricMatcher<number> {
-  private precision: number;
+  private readonly precision: number;
 
   constructor(sample: number, precision = 2, inverse = false) {
     if (!isA('Number', sample)) {

packages/expect/src/index.ts

@@ -39,7 +39,6 @@ import toThrowMatchers, {
   createMatcher as createThrowMatcher,
 } from './toThrowMatchers';
 import type {
-  AsyncExpectationResult,
   Expect,
   ExpectationResult,
   MatcherContext,
@@ -363,19 +362,16 @@ const makeThrowingMatcher = (
             })();
 
       if (isPromise(potentialResult)) {
-        const asyncResult = potentialResult as AsyncExpectationResult;
         const asyncError = new JestAssertionError();
         if (Error.captureStackTrace) {
           Error.captureStackTrace(asyncError, throwingMatcher);
         }
 
-        return asyncResult
+        return potentialResult
           .then(aResult => processResult(aResult, asyncError))
           .catch(handleError);
       } else {
-        const syncResult = potentialResult as SyncExpectationResult;
-
-        return processResult(syncResult);
+        return processResult(potentialResult);
       }
     } catch (error: any) {
       return handleError(error);

packages/jest-config/src/normalize.ts

@@ -108,8 +108,8 @@ const mergeGlobalsWithPreset = (
   options: Config.InitialOptions,
   preset: Config.InitialOptions,
 ) => {
-  if (options['globals'] && preset['globals']) {
-    options['globals'] = merge(preset['globals'], options['globals']);
+  if (options.globals && preset.globals) {
+    options.globals = merge(preset.globals, options.globals);
   }
 };
 
@@ -1061,14 +1061,14 @@ export default async function normalize(
   );
   newOptions.maxWorkers = getMaxWorkers(argv, options);
 
-  if (newOptions.testRegex!.length && options.testMatch) {
+  if (newOptions.testRegex.length > 0 && options.testMatch) {
     throw createConfigError(
       `  Configuration options ${chalk.bold('testMatch')} and` +
         ` ${chalk.bold('testRegex')} cannot be used together.`,
     );
   }
 
-  if (newOptions.testRegex!.length && !options.testMatch) {
+  if (newOptions.testRegex.length > 0 && !options.testMatch) {
     // Prevent the default testMatch conflicting with any explicitly
     // configured `testRegex` value
     newOptions.testMatch = [];
@@ -1101,7 +1101,7 @@ export default async function normalize(
         if (
           micromatch(
             [replacePathSepForGlob(path.relative(options.rootDir, filename))],
-            newOptions.collectCoverageFrom!,
+            newOptions.collectCoverageFrom,
           ).length === 0
         ) {
           return patterns;

packages/jest-config/src/utils.ts

@@ -48,7 +48,7 @@ export const resolve = (
     );
   }
   /// can cast as string since nulls will be thrown
-  return module as string;
+  return module!;
 };
 
 export const escapeGlobCharacters = (path: string): string =>
@@ -106,10 +106,7 @@ export const _replaceRootDirTags = <T extends ReplaceRootDirConfigValues>(
         return config;
       }
 
-      return _replaceRootDirInObject(
-        rootDir,
-        config as ReplaceRootDirConfigObj,
-      ) as T;
+      return _replaceRootDirInObject(rootDir, config) as T;
     case 'string':
       return replaceRootDirInPath(rootDir, config) as T;
   }

packages/jest-console/src/BufferedConsole.ts

@@ -19,7 +19,7 @@ import type {
 } from './types';
 
 export default class BufferedConsole extends Console {
-  private _buffer: ConsoleBuffer = [];
+  private readonly _buffer: ConsoleBuffer = [];
   private _counters: LogCounters = {};
   private _timers: LogTimers = {};
   private _groupDepth = 0;

packages/jest-console/src/CustomConsole.ts

@@ -15,9 +15,9 @@ import type {LogCounters, LogMessage, LogTimers, LogType} from './types';
 type Formatter = (type: LogType, message: LogMessage) => string;
 
 export default class CustomConsole extends Console {
-  private _stdout: NodeJS.WriteStream;
-  private _stderr: NodeJS.WriteStream;
-  private _formatBuffer: Formatter;
+  private readonly _stdout: NodeJS.WriteStream;
+  private readonly _stderr: NodeJS.WriteStream;
+  private readonly _formatBuffer: Formatter;
   private _counters: LogCounters = {};
   private _timers: LogTimers = {};
   private _groupDepth = 0;