chore: add explicit-module-boundary-types lint rule (#9539)

Author: SimenB

.eslintrc.js

@@ -73,6 +73,24 @@ module.exports = {
         'import/no-extraneous-dependencies': 0,
       },
     },
+    {
+      files: 'packages/**/*.ts',
+      rules: {
+        '@typescript-eslint/explicit-module-boundary-types': 2,
+      },
+    },
+    {
+      files: [
+        '**/__tests__/**',
+        '**/__mocks__/**',
+        'packages/jest-jasmine2/src/jasmine/**/*',
+        'packages/expect/src/jasmineUtils.ts',
+        '**/vendor/**/*',
+      ],
+      rules: {
+        '@typescript-eslint/explicit-module-boundary-types': 0,
+      },
+    },
     {
       files: [
         'packages/jest-jasmine2/src/jasmine/**/*',

package.json

@@ -17,8 +17,8 @@
     "@types/jest": "24.0.2",
     "@types/node": "*",
     "@types/which": "^1.3.2",
-    "@typescript-eslint/eslint-plugin": "^2.2.0",
-    "@typescript-eslint/parser": "^2.2.0",
+    "@typescript-eslint/eslint-plugin": "^2.19.0",
+    "@typescript-eslint/parser": "^2.19.0",
     "ansi-regex": "^5.0.0",
     "ansi-styles": "^4.2.0",
     "babel-eslint": "^10.0.3",

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

@@ -155,7 +155,7 @@ FUNCTIONS.deepUnmock = args => args.length === 1 && args[0].isStringLiteral();
 FUNCTIONS.disableAutomock = FUNCTIONS.enableAutomock = args =>
   args.length === 0;
 
-export default () => {
+export default (): {visitor: Visitor} => {
   const shouldHoistExpression = (expr: NodePath): boolean => {
     if (!expr.isCallExpression()) {
       return false;

packages/diff-sequences/src/index.ts

@@ -785,7 +785,7 @@ export default (
   bLength: number,
   isCommon: IsCommon,
   foundSubsequence: FoundSubsequence,
-) => {
+): void => {
   validateLength('aLength', aLength);
   validateLength('bLength', bLength);
   validateCallback('isCommon', isCommon);

packages/expect/src/asymmetricMatchers.ts

@@ -239,21 +239,23 @@ class StringMatching extends AsymmetricMatcher<RegExp> {
   }
 }
 
-export const any = (expectedObject: any) => new Any(expectedObject);
-export const anything = () => new Anything();
-export const arrayContaining = (sample: Array<unknown>) =>
+export const any = (expectedObject: unknown): Any => new Any(expectedObject);
+export const anything = (): Anything => new Anything();
+export const arrayContaining = (sample: Array<unknown>): ArrayContaining =>
   new ArrayContaining(sample);
-export const arrayNotContaining = (sample: Array<unknown>) =>
+export const arrayNotContaining = (sample: Array<unknown>): ArrayContaining =>
   new ArrayContaining(sample, true);
-export const objectContaining = (sample: Record<string, any>) =>
-  new ObjectContaining(sample);
-export const objectNotContaining = (sample: Record<string, any>) =>
-  new ObjectContaining(sample, true);
-export const stringContaining = (expected: string) =>
+export const objectContaining = (
+  sample: Record<string, any>,
+): ObjectContaining => new ObjectContaining(sample);
+export const objectNotContaining = (
+  sample: Record<string, any>,
+): ObjectContaining => new ObjectContaining(sample, true);
+export const stringContaining = (expected: string): StringContaining =>
   new StringContaining(expected);
-export const stringNotContaining = (expected: string) =>
+export const stringNotContaining = (expected: string): StringContaining =>
   new StringContaining(expected, true);
-export const stringMatching = (expected: string | RegExp) =>
+export const stringMatching = (expected: string | RegExp): StringMatching =>
   new StringMatching(expected);
-export const stringNotMatching = (expected: string | RegExp) =>
+export const stringNotMatching = (expected: string | RegExp): StringMatching =>
   new StringMatching(expected, true);

packages/expect/src/jestMatchersObject.ts

@@ -31,19 +31,20 @@ if (!global.hasOwnProperty(JEST_MATCHERS_OBJECT)) {
   });
 }
 
-export const getState = () => (global as any)[JEST_MATCHERS_OBJECT].state;
+export const getState = (): any => (global as any)[JEST_MATCHERS_OBJECT].state;
 
-export const setState = (state: object) => {
+export const setState = (state: object): void => {
   Object.assign((global as any)[JEST_MATCHERS_OBJECT].state, state);
 };
 
-export const getMatchers = () => (global as any)[JEST_MATCHERS_OBJECT].matchers;
+export const getMatchers = (): MatchersObject =>
+  (global as any)[JEST_MATCHERS_OBJECT].matchers;
 
 export const setMatchers = (
   matchers: MatchersObject,
   isInternal: boolean,
   expect: Expect,
-) => {
+): void => {
   Object.keys(matchers).forEach(key => {
     const matcher = matchers[key];
     Object.defineProperty(matcher, INTERNAL_MATCHER_FLAG, {

packages/expect/src/print.ts

@@ -92,24 +92,24 @@ export const printCloseTo = (
 export const printExpectedConstructorName = (
   label: string,
   expected: Function,
-) => printConstructorName(label, expected, false, true) + '\n';
+): string => printConstructorName(label, expected, false, true) + '\n';
 
 export const printExpectedConstructorNameNot = (
   label: string,
   expected: Function,
-) => printConstructorName(label, expected, true, true) + '\n';
+): string => printConstructorName(label, expected, true, true) + '\n';
 
 export const printReceivedConstructorName = (
   label: string,
   received: Function,
-) => printConstructorName(label, received, false, false) + '\n';
+): string => printConstructorName(label, received, false, false) + '\n';
 
 // Do not call function if received is equal to expected.
 export const printReceivedConstructorNameNot = (
   label: string,
   received: Function,
   expected: Function,
-) =>
+): string =>
   typeof expected.name === 'string' &&
   expected.name.length !== 0 &&
   typeof received.name === 'string' &&

packages/expect/src/toThrowMatchers.ts

@@ -27,6 +27,7 @@ import {
   printReceivedStringContainExpectedSubstring,
 } from './print';
 import {
+  ExpectationResult,
   MatcherState,
   MatchersObject,
   RawMatcherFn,
@@ -75,7 +76,12 @@ export const createMatcher = (
   matcherName: string,
   fromPromise?: boolean,
 ): RawMatcherFn =>
-  function(this: MatcherState, received: Function, expected: any) {
+  // eslint-disable-next-line @typescript-eslint/explicit-module-boundary-types
+  function(
+    this: MatcherState,
+    received: Function,
+    expected: any,
+  ): ExpectationResult {
     const options = {
       isNot: this.isNot,
       promise: this.promise,

packages/expect/src/utils.ts

@@ -44,7 +44,7 @@ const hasGetterFromConstructor = (object: object, key: string) => {
   return descriptor !== undefined && typeof descriptor.get === 'function';
 };
 
-export const hasOwnProperty = (object: object, key: string) =>
+export const hasOwnProperty = (object: object, key: string): boolean =>
   Object.prototype.hasOwnProperty.call(object, key) ||
   hasGetterFromConstructor(object, key);
 
@@ -104,6 +104,7 @@ export const getPath = (
 
 // Strip properties from object that are not present in the subset. Useful for
 // printing the diff for toMatchObject() without adding unrelated noise.
+// eslint-disable-next-line @typescript-eslint/explicit-module-boundary-types
 export const getObjectSubset = (
   object: any,
   subset: any,
@@ -147,12 +148,13 @@ const IteratorSymbol = Symbol.iterator;
 const hasIterator = (object: any) =>
   !!(object != null && object[IteratorSymbol]);
 
+// eslint-disable-next-line @typescript-eslint/explicit-module-boundary-types
 export const iterableEquality = (
   a: any,
   b: any,
   aStack: Array<any> = [],
   bStack: Array<any> = [],
-) => {
+): boolean | undefined => {
   if (
     typeof a !== 'object' ||
     typeof b !== 'object' ||
@@ -273,16 +275,17 @@ const isObjectWithKeys = (a: any) =>
   !(a instanceof Array) &&
   !(a instanceof Date);
 
+// eslint-disable-next-line @typescript-eslint/explicit-module-boundary-types
 export const subsetEquality = (
   object: any,
   subset: any,
-): undefined | boolean => {
+): boolean | undefined => {
   // subsetEquality needs to keep track of the references
   // it has already visited to avoid infinite loops in case
   // there are circular references in the subset passed to it.
   const subsetEqualityWithContext = (
     seenReferences: WeakMap<object, boolean> = new WeakMap(),
-  ) => (object: any, subset: any): undefined | boolean => {
+  ) => (object: any, subset: any): boolean | undefined => {
     if (!isObjectWithKeys(subset)) {
       return undefined;
     }
@@ -314,15 +317,19 @@ export const subsetEquality = (
   return subsetEqualityWithContext()(object, subset);
 };
 
-export const typeEquality = (a: any, b: any) => {
+// eslint-disable-next-line @typescript-eslint/explicit-module-boundary-types
+export const typeEquality = (a: any, b: any): boolean | undefined => {
   if (a == null || b == null || a.constructor === b.constructor) {
     return undefined;
   }
 
   return false;
 };
 
-export const sparseArrayEquality = (a: unknown, b: unknown) => {
+export const sparseArrayEquality = (
+  a: unknown,
+  b: unknown,
+): boolean | undefined => {
   if (!Array.isArray(a) || !Array.isArray(b)) {
     return undefined;
   }
@@ -347,7 +354,7 @@ export const partition = <T>(
 };
 
 // Copied from https://github.com/graingert/angular.js/blob/a43574052e9775cbc1d7dd8a086752c979b0f020/src/Angular.js#L685-L693
-export const isError = (value: unknown) => {
+export const isError = (value: unknown): value is Error => {
   switch (Object.prototype.toString.call(value)) {
     case '[object Error]':
       return true;
@@ -360,13 +367,14 @@ export const isError = (value: unknown) => {
   }
 };
 
-export function emptyObject(obj: any) {
+// eslint-disable-next-line @typescript-eslint/explicit-module-boundary-types
+export function emptyObject(obj: any): boolean {
   return obj && typeof obj === 'object' ? !Object.keys(obj).length : false;
 }
 
 const MULTILINE_REGEXP = /[\r\n]/;
 
-export const isOneline = (expected: any, received: any): boolean =>
+export const isOneline = (expected: unknown, received: unknown): boolean =>
   typeof expected === 'string' &&
   typeof received === 'string' &&
   (!MULTILINE_REGEXP.test(expected) || !MULTILINE_REGEXP.test(received));

packages/jest-circus/src/globalErrorHandlers.ts

@@ -28,7 +28,7 @@ export const injectGlobalErrorHandlers = (
 export const restoreGlobalErrorHandlers = (
   parentProcess: NodeJS.Process,
   originalErrorHandlers: Circus.GlobalErrorHandlers,
-) => {
+): void => {
   parentProcess.removeListener('uncaughtException', uncaught);
   parentProcess.removeListener('unhandledRejection', uncaught);
 

packages/jest-circus/src/legacy-code-todo-rewrite/jestAdapterInit.ts

@@ -34,6 +34,8 @@ import globals from '..';
 
 type Process = NodeJS.Process;
 
+// TODO: hard to type
+// eslint-disable-next-line @typescript-eslint/explicit-module-boundary-types
 export const initialize = ({
   config,
   environment,

packages/jest-circus/src/legacy-code-todo-rewrite/jestExpect.ts

@@ -15,7 +15,7 @@ import {
   toThrowErrorMatchingSnapshot,
 } from 'jest-snapshot';
 
-export default (config: {expand: boolean}) => {
+export default (config: {expand: boolean}): void => {
   global.expect = expect;
   expect.setState({
     expand: config.expand,

packages/jest-circus/src/utils.ts

@@ -73,11 +73,15 @@ const hasEnabledTest = (describeBlock: Circus.DescribeBlock): boolean => {
   return hasOwnEnabledTests || describeBlock.children.some(hasEnabledTest);
 };
 
-export const getAllHooksForDescribe = (describe: Circus.DescribeBlock) => {
-  const result: {
-    beforeAll: Array<Circus.Hook>;
-    afterAll: Array<Circus.Hook>;
-  } = {
+type DescribeHooks = {
+  beforeAll: Array<Circus.Hook>;
+  afterAll: Array<Circus.Hook>;
+};
+
+export const getAllHooksForDescribe = (
+  describe: Circus.DescribeBlock,
+): DescribeHooks => {
+  const result: DescribeHooks = {
     afterAll: [],
     beforeAll: [],
   };
@@ -98,11 +102,13 @@ export const getAllHooksForDescribe = (describe: Circus.DescribeBlock) => {
   return result;
 };
 
-export const getEachHooksForTest = (test: Circus.TestEntry) => {
-  const result: {
-    beforeEach: Array<Circus.Hook>;
-    afterEach: Array<Circus.Hook>;
-  } = {afterEach: [], beforeEach: []};
+type TestHooks = {
+  beforeEach: Array<Circus.Hook>;
+  afterEach: Array<Circus.Hook>;
+};
+
+export const getEachHooksForTest = (test: Circus.TestEntry): TestHooks => {
+  const result: TestHooks = {afterEach: [], beforeEach: []};
   let block: Circus.DescribeBlock | undefined | null = test.parent;
 
   do {
@@ -298,7 +304,7 @@ const makeTestResults = (
 
 // Return a string that identifies the test (concat of parent describe block
 // names + test title)
-export const getTestID = (test: Circus.TestEntry) => {
+export const getTestID = (test: Circus.TestEntry): string => {
   const titles = [];
   let parent: Circus.TestEntry | Circus.DescribeBlock | undefined = test;
   do {
@@ -341,7 +347,7 @@ export const addErrorToEachTestUnderDescribe = (
   describeBlock: Circus.DescribeBlock,
   error: Circus.Exception,
   asyncError: Circus.Exception,
-) => {
+): void => {
   for (const test of describeBlock.tests) {
     test.errors.push([error, asyncError]);
   }

packages/jest-cli/src/cli/args.ts

@@ -9,7 +9,7 @@ import {Config} from '@jest/types';
 import {isJSONString} from 'jest-config';
 import isCI = require('is-ci');
 
-export const check = (argv: Config.Argv) => {
+export const check = (argv: Config.Argv): true => {
   if (argv.runInBand && argv.hasOwnProperty('maxWorkers')) {
     throw new Error(
       'Both --runInBand and --maxWorkers were specified, but these two ' +

packages/jest-cli/src/cli/index.ts

@@ -19,7 +19,10 @@ import {sync as realpath} from 'realpath-native';
 import init from '../init';
 import * as args from './args';
 
-export async function run(maybeArgv?: Array<string>, project?: Config.Path) {
+export async function run(
+  maybeArgv?: Array<string>,
+  project?: Config.Path,
+): Promise<void> {
   try {
     const argv: Config.Argv = buildArgv(maybeArgv);
 

packages/jest-cli/src/init/index.ts

@@ -34,7 +34,9 @@ type PromptsResults = {
 
 const getConfigFilename = (ext: string) => JEST_CONFIG_BASE_NAME + ext;
 
-export default async (rootDir: string = realpath(process.cwd())) => {
+export default async (
+  rootDir: string = realpath(process.cwd()),
+): Promise<void> => {
   // prerequisite checks
   const projectPackageJsonPath: string = path.join(rootDir, PACKAGE_JSON);