feat: support . in exports field

CHANGELOG.md

@@ -3,6 +3,7 @@
 ### Features
 
 - `[jest-config]` Add `testEnvironmentOptions.html` to apply to jsdom input ([11950](https://github.com/facebook/jest/pull/11950))
+- `[jest-resolver]` Support default export (`.`) in `exports` field _if_ `main` is missing ([#11919](https://github.com/facebook/jest/pull/11919))
 
 ### Fixes
 

e2e/__tests__/resolveConditions.test.ts

@@ -7,15 +7,10 @@
 
 import {resolve} from 'path';
 import {onNodeVersions} from '@jest/test-utils';
-import {runYarnInstall} from '../Utils';
 import runJest from '../runJest';
 
 const dir = resolve(__dirname, '..', 'resolve-conditions');
 
-beforeAll(() => {
-  runYarnInstall(dir);
-});
-
 // The versions where vm.Module exists and commonjs with "exports" is not broken
 onNodeVersions('>=12.16.0', () => {
   test('resolves package exports correctly with custom resolver', () => {

e2e/resolve-conditions/__tests__/browser.test.mjs

@@ -7,7 +7,7 @@
  * @jest-environment <rootDir>/browser-env.js
  */
 
-import {fn} from '../fake-dual-dep';
+import {fn} from 'fake-dual-dep';
 
 test('returns correct message', () => {
   expect(fn()).toEqual('hello from browser');

e2e/resolve-conditions/__tests__/node.test.mjs

@@ -7,7 +7,7 @@
  * @jest-environment <rootDir>/node-env.js
  */
 
-import {fn} from '../fake-dual-dep';
+import {fn} from 'fake-dual-dep';
 
 test('returns correct message', () => {
   expect(fn()).toEqual('hello from node');

e2e/resolve-conditions/__tests__/resolveCjs.test.cjs

@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-const {fn} = require('../fake-dep');
+const {fn} = require('fake-dep');
 
 test('returns correct message', () => {
   expect(fn()).toEqual('hello from CJS');

e2e/resolve-conditions/__tests__/resolveEsm.test.mjs

@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-import {fn} from '../fake-dep';
+import {fn} from 'fake-dep';
 
 test('returns correct message', () => {
   expect(fn()).toEqual('hello from ESM');

e2e/resolve-conditions/package.json

@@ -6,13 +6,9 @@
       "mjs",
       "json"
     ],
-    "resolver": "<rootDir>/resolver.js",
     "testMatch": [
       "<rootDir>/**/*.test.*"
     ],
     "transform": {}
-  },
-  "dependencies": {
-    "resolve.exports": "^1.1.0"
   }
 }

packages/jest-resolve/package.json

@@ -22,6 +22,7 @@
     "jest-util": "^27.2.5",
     "jest-validate": "^27.2.5",
     "resolve": "^1.20.0",
+    "resolve.exports": "^1.1.0",
     "slash": "^3.0.0"
   },
   "devDependencies": {

packages/jest-resolve/src/__mocks__/package.json

@@ -0,0 +1,6 @@
+{
+  "name": "__mocks__",
+  "version": "1.0.0",
+  "dependencies": {
+  }
+}

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

@@ -126,26 +126,61 @@ describe('findNodeModule', () => {
     });
   });
 
-  it('passes packageFilter to the resolve module when using the default resolver', () => {
+  it('wraps passed 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.findNodeModule('./test', {
+      basedir: path.resolve(__dirname, '../__mocks__/'),
       resolver: require.resolve('../__mocks__/userResolver'),
     });
 
-    expect(mockResolveSync).toHaveBeenCalledWith(
-      'test',
-      expect.objectContaining({
-        packageFilter,
-      }),
+    expect(packageFilter).toHaveBeenCalledWith(
+      expect.objectContaining({name: '__mocks__'}),
+      expect.any(String),
     );
   });
+
+  describe('conditions', () => {
+    const conditionsRoot = path.resolve(__dirname, '../__mocks__/conditions');
+
+    test('resolves without exports, just main', () => {
+      const result = Resolver.findNodeModule('main', {
+        basedir: conditionsRoot,
+        conditions: ['require'],
+      });
+
+      expect(result).toEqual(
+        path.resolve(conditionsRoot, './node_modules/main/file.js'),
+      );
+    });
+
+    test('resolves with import', () => {
+      const result = Resolver.findNodeModule('import', {
+        basedir: conditionsRoot,
+        conditions: ['import'],
+      });
+
+      expect(result).toEqual(
+        path.resolve(conditionsRoot, './node_modules/import/file.js'),
+      );
+    });
+
+    test('resolves with require', () => {
+      const result = Resolver.findNodeModule('require', {
+        basedir: conditionsRoot,
+        conditions: ['require'],
+      });
+
+      expect(result).toEqual(
+        path.resolve(conditionsRoot, './node_modules/require/file.js'),
+      );
+    });
+  });
 });
 
 describe('resolveModule', () => {

packages/jest-resolve/src/defaultResolver.ts

@@ -5,8 +5,13 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+import {resolve} from 'path';
 import pnpResolver from 'jest-pnp-resolver';
-import {Opts as ResolveOpts, sync as resolveSync} from 'resolve';
+import {sync as resolveSync} from 'resolve';
+import {
+  Options as ResolveExportsOptions,
+  resolve as resolveExports,
+} from 'resolve.exports';
 import type {Config} from '@jest/types';
 import {
   PkgJson,
@@ -16,13 +21,19 @@ import {
   realpathSync,
 } from './fileWalkers';
 
-interface ResolverOptions extends ResolveOpts {
+// copy from `resolve`'s types so we don't have their types in our definition
+// files
+interface ResolverOptions {
   basedir: Config.Path;
   browser?: boolean;
   conditions?: Array<string>;
   defaultResolver: typeof defaultResolver;
   extensions?: Array<string>;
+  moduleDirectory?: Array<string>;
+  paths?: Array<Config.Path>;
   rootDir?: Config.Path;
+  packageFilter?: (pkg: PkgJson, dir: string) => PkgJson;
+  pathFilter?: (pkg: PkgJson, path: string, relativePath: string) => string;
 }
 
 // https://github.com/facebook/jest/pull/10617
@@ -48,6 +59,10 @@ export default function defaultResolver(
     ...options,
     isDirectory,
     isFile,
+    packageFilter: createPackageFilter(
+      options.conditions,
+      options.packageFilter,
+    ),
     preserveSymlinks: false,
     readPackageSync,
     realpathSync,
@@ -65,3 +80,47 @@ export default function defaultResolver(
 function readPackageSync(_: unknown, file: Config.Path): PkgJson {
   return readPackageCached(file);
 }
+
+function createPackageFilter(
+  conditions?: Array<string>,
+  userFilter?: ResolverOptions['packageFilter'],
+): ResolverOptions['packageFilter'] {
+  function attemptExportsFallback(pkg: PkgJson) {
+    const options: ResolveExportsOptions = conditions
+      ? {conditions, unsafe: true}
+      : // no conditions were passed - let's assume this is Jest internal and it should be `require`
+        {browser: false, require: true};
+
+    try {
+      return resolveExports(pkg, '.', options);
+    } catch {
+      return undefined;
+    }
+  }
+
+  return function packageFilter(pkg, packageDir) {
+    let filteredPkg = pkg;
+
+    if (userFilter) {
+      filteredPkg = userFilter(filteredPkg, packageDir);
+    }
+
+    if (filteredPkg.main != null) {
+      return filteredPkg;
+    }
+
+    const indexInRoot = resolve(packageDir, './index.js');
+
+    // if the module contains an `index.js` file in root, `resolve` will request
+    // that if there is no `main`. Since we don't wanna break that, add this
+    // check
+    if (isFile(indexInRoot)) {
+      return filteredPkg;
+    }
+
+    return {
+      ...filteredPkg,
+      main: attemptExportsFallback(filteredPkg),
+    };
+  };
+}

yarn.lock

@@ -13026,6 +13026,7 @@ fsevents@^1.2.7:
     jest-util: ^27.2.5
     jest-validate: ^27.2.5
     resolve: ^1.20.0
+    resolve.exports: ^1.1.0
     slash: ^3.0.0
   languageName: unknown
   linkType: soft
@@ -18944,6 +18945,13 @@ react-native@0.64.0:
   languageName: node
   linkType: hard
 
+"resolve.exports@npm:^1.1.0":
+  version: 1.1.0
+  resolution: "resolve.exports@npm:1.1.0"
+  checksum: d04d2ce651fac14fe6ba13b377690f790cbbe91e6211b8fbec97ee08282e278875c74073a9b6243143a64e33d95eefb479e1dd4965664edc73b28b712100b36c
+  languageName: node
+  linkType: hard
+
 "resolve@^1.1.6, resolve@^1.10.0, resolve@^1.14.2, resolve@^1.15.0, resolve@^1.19.0, resolve@^1.20.0, resolve@^1.3.2":
   version: 1.20.0
   resolution: "resolve@npm:1.20.0"