Allow the cli to use a string for --maxWorkers

CHANGELOG.md

@@ -7,9 +7,11 @@
 - `[jest-cli]` Improve chai support (with detailed output, to match jest exceptions) ([#8454](https://github.com/facebook/jest/pull/8454))
 - `[*]` Manage the global timeout with `--testTimeout` command line argument. ([#8456](https://github.com/facebook/jest/pull/8456))
 - `[pretty-format]` Render custom displayName of memoized components
+- `[jest-validate]` Allow `maxWorkers` as part of the `jest.config.js` ([#8565](https://github.com/facebook/jest/pull/8565))
 
 ### Fixes
 
+- `[jest-cli]` Allow `--maxWorkers` to work with % input again ([#8565](https://github.com/facebook/jest/pull/8565))
 - `[babel-plugin-jest-hoist]` Expand list of whitelisted globals in global mocks ([#8429](https://github.com/facebook/jest/pull/8429)
 - `[jest-core]` Make watch plugin initialization errors look nice ([#8422](https://github.com/facebook/jest/pull/8422))
 - `[jest-snapshot]` Prevent inline snapshots from drifting when inline snapshots are updated ([#8492](https://github.com/facebook/jest/pull/8492))

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

@@ -50,10 +50,15 @@ describe('check', () => {
   it('raises an exception if maxWorkers is specified with no number', () => {
     const argv = ({maxWorkers: undefined} as unknown) as Config.Argv;
     expect(() => check(argv)).toThrow(
-      'The --maxWorkers (-w) option requires a number to be specified',
+      'The --maxWorkers (-w) option requires a number or string to be specified',
     );
   });
 
+  it('allows maxWorkers to be a %', () => {
+    const argv = ({maxWorkers: '50%'} as unknown) as Config.Argv;
+    expect(() => check(argv)).not.toThrow();
+  });
+
   it('raises an exception if config is not a valid JSON string', () => {
     const argv = {config: 'x:1'} as Config.Argv;
     expect(() => check(argv)).toThrow(

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

@@ -42,8 +42,9 @@ export const check = (argv: Config.Argv) => {
 
   if (argv.hasOwnProperty('maxWorkers') && argv.maxWorkers === undefined) {
     throw new Error(
-      'The --maxWorkers (-w) option requires a number to be specified.\n' +
+      'The --maxWorkers (-w) option requires a number or string to be specified.\n' +
         'Example usage: jest --maxWorkers 2\n' +
+        'Example usage: jest --maxWorkers 50%\n' +
         'Or did you mean --watch?',
     );
   }
@@ -349,7 +350,7 @@ export const options = {
       'will spawn for running tests. This defaults to the number of the ' +
       'cores available on your machine. (its usually best not to override ' +
       'this default)',
-    type: 'number' as 'number',
+    type: 'string' as 'string',
   },
   moduleDirectories: {
     description:

packages/jest-cli/src/init/__tests__/__snapshots__/init.test.js.snap

@@ -81,6 +81,9 @@ module.exports = {
   // A set of global variables that need to be available in all test environments
   // globals: {},
 
+  // The maximum amount of workers used to run your tests. Can be specified as % or a number. E.g. maxWorkers: 10% will use 10% of your CPU amount + 1 as the maximum worker number. maxWorkers: 2 will use a maximum of 2 workers.
+  // maxWorkers: \\"50%\\",
+
   // An array of directory names to be searched recursively up from the requiring module's location
   // moduleDirectories: [
   //   \\"node_modules\\"

packages/jest-config/src/Defaults.ts

@@ -40,6 +40,7 @@ const defaultOptions: Config.DefaultOptions = {
     throwOnModuleCollision: false,
   },
   maxConcurrency: 5,
+  maxWorkers: '50%',
   moduleDirectories: ['node_modules'],
   moduleFileExtensions: ['js', 'json', 'jsx', 'ts', 'tsx', 'node'],
   moduleNameMapper: {},

packages/jest-config/src/Descriptions.ts

@@ -37,6 +37,8 @@ const descriptions: {[key in keyof Config.InitialOptions]: string} = {
     'A path to a module which exports an async function that is triggered once after all test suites',
   globals:
     'A set of global variables that need to be available in all test environments',
+  maxWorkers:
+    'The maximum amount of workers used to run your tests. Can be specified as % or a number. E.g. maxWorkers: 10% will use 10% of your CPU amount + 1 as the maximum worker number. maxWorkers: 2 will use a maximum of 2 workers.',
   moduleDirectories:
     "An array of directory names to be searched recursively up from the requiring module's location",
   moduleFileExtensions: 'An array of file extensions your modules use',

packages/jest-config/src/ValidConfig.ts

@@ -63,6 +63,7 @@ const initialOptions: Config.InitialOptions = {
   lastCommit: false,
   logHeapUsage: true,
   maxConcurrency: 5,
+  maxWorkers: '50%',
   moduleDirectories: ['node_modules'],
   moduleFileExtensions: ['js', 'json', 'jsx', 'ts', 'tsx', 'node'],
   moduleLoader: '<rootDir>',

packages/jest-config/src/getMaxWorkers.ts

@@ -10,29 +10,34 @@ import {Config} from '@jest/types';
 
 export default function getMaxWorkers(
   argv: Partial<Pick<Config.Argv, 'maxWorkers' | 'runInBand' | 'watch'>>,
+  defaultOptions?: Partial<Pick<Config.Argv, 'maxWorkers'>>,
 ): number {
   if (argv.runInBand) {
     return 1;
   } else if (argv.maxWorkers) {
-    // TODO: How to type this properly? Should probably use `coerce` from `yargs`
-    const maxWorkers = argv.maxWorkers;
-    const parsed = parseInt(maxWorkers as string, 10);
-
-    if (
-      typeof maxWorkers === 'string' &&
-      maxWorkers.trim().endsWith('%') &&
-      parsed > 0 &&
-      parsed <= 100
-    ) {
-      const cpus = os.cpus().length;
-      const workers = Math.floor((parsed / 100) * cpus);
-      return workers >= 1 ? workers : 1;
-    }
-
-    return parsed > 0 ? parsed : 1;
+    return parseWorkers(argv.maxWorkers);
+  } else if (defaultOptions && defaultOptions.maxWorkers) {
+    return parseWorkers(defaultOptions.maxWorkers);
   } else {
     // In watch mode, Jest should be unobtrusive and not use all available CPUs.
     const cpus = os.cpus() ? os.cpus().length : 1;
     return Math.max(argv.watch ? Math.floor(cpus / 2) : cpus - 1, 1);
   }
 }
+
+const parseWorkers = (maxWorkers: string | number): number => {
+  const parsed = parseInt(maxWorkers.toString(), 10);
+
+  if (
+    typeof maxWorkers === 'string' &&
+    maxWorkers.trim().endsWith('%') &&
+    parsed > 0 &&
+    parsed <= 100
+  ) {
+    const cpus = os.cpus().length;
+    const workers = Math.floor((parsed / 100) * cpus);
+    return workers >= 1 ? workers : 1;
+  }
+
+  return parsed > 0 ? parsed : 1;
+};

packages/jest-config/src/normalize.ts

@@ -928,7 +928,7 @@ export default function normalize(
     (newOptions.maxConcurrency as unknown) as string,
     10,
   );
-  newOptions.maxWorkers = getMaxWorkers(argv);
+  newOptions.maxWorkers = getMaxWorkers(argv, options);
 
   if (newOptions.testRegex!.length && options.testMatch) {
     throw createConfigError(

packages/jest-types/src/Config.ts

@@ -55,6 +55,7 @@ export type DefaultOptions = {
   globalSetup: string | null | undefined;
   globalTeardown: string | null | undefined;
   haste: HasteConfig;
+  maxWorkers: number | string;
   maxConcurrency: number;
   moduleDirectories: Array<string>;
   moduleFileExtensions: Array<string>;
@@ -156,6 +157,7 @@ export type InitialOptions = {
   listTests?: boolean;
   mapCoverage?: boolean;
   maxConcurrency?: number;
+  maxWorkers: number | string;
   moduleDirectories?: Array<string>;
   moduleFileExtensions?: Array<string>;
   moduleLoader?: Path;

packages/jest-validate/src/validate.ts

@@ -6,8 +6,8 @@
  */
 
 import {ValidationOptions} from './types';
-
 import defaultConfig from './defaultConfig';
+import {ValidationError} from './utils';
 
 let hasDeprecationWarnings = false;
 
@@ -46,6 +46,21 @@ const _validate = (
       );
 
       hasDeprecationWarnings = hasDeprecationWarnings || isDeprecatedKey;
+    } else if (allowsMultipleTypes(key)) {
+      const value = config[key];
+
+      if (
+        typeof options.condition === 'function' &&
+        typeof options.error === 'function'
+      ) {
+        if (key === 'maxWorkers' && !isOfTypeStringOrNumber(value)) {
+          throw new ValidationError(
+            'Validation Error',
+            `${key} has to be of type string or number`,
+            `maxWorkers=50% or\nmaxWorkers=3`,
+          );
+        }
+      }
     } else if (Object.hasOwnProperty.call(exampleConfig, key)) {
       if (
         typeof options.condition === 'function' &&
@@ -76,6 +91,10 @@ const _validate = (
   return {hasDeprecationWarnings};
 };
 
+const allowsMultipleTypes = (key: string): boolean => key === 'maxWorkers';
+const isOfTypeStringOrNumber = (value: any): boolean =>
+  typeof value === 'number' || typeof value === 'string';
+
 const validate = (config: Record<string, any>, options: ValidationOptions) => {
   hasDeprecationWarnings = false;