[jest-resolve] Add support for packageFilter for custom resolvers (#…

…10393)

CHANGELOG.md

@@ -2,6 +2,8 @@
 
 ### Features
 
+- `[jest-resolve]` Add support for `packageFilter` on custom resolver ([#10393](https://github.com/facebook/jest/pull/10393))
+
 ### Fixes
 
 - `[pretty-format]` Handle `tagName` not being a string ([#10397](https://github.com/facebook/jest/pull/10397))

docs/Configuration.md

@@ -693,6 +693,7 @@ This option allows the use of a custom resolver. This resolver must be a node mo
   "extensions": [string],
   "moduleDirectory": [string],
   "paths": [string],
+  "packageFilter": "function(pkg, pkgdir)",
   "rootDir": [string]
 }
 ```
@@ -712,6 +713,36 @@ For example, if you want to respect Browserify's [`"browser"` field](https://git
 }
 ```
 
+By combining `defaultResolver` and `packageFilter` we can implement a `package.json` "pre-processor" that allows us to change how the default resolver will resolve modules. For example, imagine we want to use the field `"module"` if it is present, otherwise fallback to `"main"`:
+
+```json
+{
+  ...
+  "jest": {
+    "resolver": "my-module-resolve"
+  }
+}
+```
+
+```js
+// my-module-resolve package
+
+module.exports = (request, options) => {
+  // Call the defaultResolver, so we leverage its cache, error handling, etc.
+  return options.defaultResolver(request, {
+    ...options,
+    // Use packageFilter to process parsed `package.json` before the resolution (see https://www.npmjs.com/package/resolve#resolveid-opts-cb)
+    packageFilter: pkg => {
+      return {
+        ...pkg,
+        // Alter the value of `main` before resolving the package
+        main: pkg.module || pkg.main,
+      };
+    },
+  });
+};
+```
+
 ### `restoreMocks` [boolean]
 
 Default: `false`

packages/jest-resolve/src/__tests__/resolve.test.ts

@@ -9,6 +9,7 @@
 import * as path from 'path';
 import * as fs from 'graceful-fs';
 import {ModuleMap} from 'jest-haste-map';
+import {sync as resolveSync} from 'resolve';
 import Resolver = require('../');
 import userResolver from '../__mocks__/userResolver';
 import nodeModulesPaths from '../nodeModulesPaths';
@@ -17,8 +18,23 @@ import type {ResolverConfig} from '../types';
 
 jest.mock('../__mocks__/userResolver');
 
+// Do not fully mock `resolve` because it is used by Jest. Doing it will crash
+// in very strange ways. Instead just spy on the method `sync`.
+jest.mock('resolve', () => {
+  const originalModule = jest.requireActual('resolve');
+  return {
+    ...originalModule,
+    sync: jest.spyOn(originalModule, 'sync'),
+  };
+});
+
+const mockResolveSync = <
+  jest.Mock<ReturnType<typeof resolveSync>, Parameters<typeof resolveSync>>
+>resolveSync;
+
 beforeEach(() => {
   userResolver.mockClear();
+  mockResolveSync.mockClear();
 });
 
 describe('isCoreModule', () => {
@@ -93,6 +109,27 @@ describe('findNodeModule', () => {
       rootDir: undefined,
     });
   });
+
+  it('passes packageFilter to the resolve module when using the default resolver', () => {
+    const packageFilter = jest.fn();
+
+    // A resolver that delegates to defaultResolver with a packageFilter implementation
+    userResolver.mockImplementation((request, opts) =>
+      opts.defaultResolver(request, {...opts, packageFilter}),
+    );
+
+    Resolver.findNodeModule('test', {
+      basedir: '/',
+      resolver: require.resolve('../__mocks__/userResolver'),
+    });
+
+    expect(mockResolveSync).toHaveBeenCalledWith(
+      'test',
+      expect.objectContaining({
+        packageFilter,
+      }),
+    );
+  });
 });
 
 describe('resolveModule', () => {

packages/jest-resolve/src/defaultResolver.ts

@@ -6,7 +6,7 @@
  */
 
 import * as fs from 'graceful-fs';
-import {sync as resolveSync} from 'resolve';
+import {Opts as ResolveOpts, sync as resolveSync} from 'resolve';
 import pnpResolver from 'jest-pnp-resolver';
 import {tryRealpath} from 'jest-util';
 import type {Config} from '@jest/types';
@@ -20,6 +20,7 @@ type ResolverOptions = {
   moduleDirectory?: Array<string>;
   paths?: Array<Config.Path>;
   rootDir?: Config.Path;
+  packageFilter?: ResolveOpts['packageFilter'];
 };
 
 declare global {
@@ -45,6 +46,7 @@ export default function defaultResolver(
     isDirectory,
     isFile,
     moduleDirectory: options.moduleDirectory,
+    packageFilter: options.packageFilter,
     paths: options.paths,
     preserveSymlinks: false,
     realpathSync,