fix: load transformers before installing require hooks (#7752)

CHANGELOG.md

@@ -15,6 +15,7 @@
 - `[jest-config]` Do not use a uuid as `name` since that breaks caching ([#7746](https://github.com/facebook/jest/pull/7746))
 - `[jest-config]` Make sure `normalize` can consume `Defaults` without warnings ([#7742](https://github.com/facebook/jest/pull/7742))
 - `[jest-config]` Allow `moduleFileExtensions` without 'js' for custom runners ([#7751](https://github.com/facebook/jest/pull/7751))
+- `[jest-cli]` Load transformers before installing require hooks ([#7752](https://github.com/facebook/jest/pull/7752)
 
 ### Chore & Maintenance
 

e2e/__tests__/globalSetup.test.js

@@ -16,16 +16,22 @@ import {cleanup} from '../Utils';
 const DIR = path.join(os.tmpdir(), 'jest-global-setup');
 const project1DIR = path.join(os.tmpdir(), 'jest-global-setup-project-1');
 const project2DIR = path.join(os.tmpdir(), 'jest-global-setup-project-2');
+const customTransformDIR = path.join(
+  os.tmpdir(),
+  'jest-global-setup-custom-transform',
+);
 
 beforeEach(() => {
   cleanup(DIR);
   cleanup(project1DIR);
   cleanup(project2DIR);
+  cleanup(customTransformDIR);
 });
 afterAll(() => {
   cleanup(DIR);
   cleanup(project1DIR);
   cleanup(project2DIR);
+  cleanup(customTransformDIR);
 });
 
 test('globalSetup is triggered once before all test suites', () => {
@@ -155,3 +161,9 @@ test('globalSetup throws with named export', () => {
     `TypeError: globalSetup file must export a function at ${setupPath}`,
   );
 });
+
+test('should not transpile the transformer', () => {
+  const {status} = runJest('global-setup-custom-transform', [`--no-cache`]);
+
+  expect(status).toBe(0);
+});

e2e/global-setup-custom-transform/__tests__/test.js

@@ -0,0 +1,25 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+'use strict';
+
+const fs = require('fs');
+const os = require('os');
+const path = require('path');
+const greeting = require('../');
+
+const DIR = path.join(os.tmpdir(), 'jest-global-setup-custom-transform');
+
+test('should exist setup file', () => {
+  const files = fs.readdirSync(DIR);
+  expect(files).toHaveLength(1);
+  const setup = fs.readFileSync(path.join(DIR, files[0]), 'utf8');
+  expect(setup).toBe('setup');
+});
+
+test('should transform imported file', () => {
+  expect(greeting).toEqual('hello, world!');
+});

e2e/global-setup-custom-transform/index.js

@@ -0,0 +1,3 @@
+// Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
+
+module.exports = 'hello!';

e2e/global-setup-custom-transform/package.json

@@ -0,0 +1,9 @@
+{
+  "jest": {
+    "testEnvironment": "node",
+    "globalSetup": "<rootDir>/setup.js",
+    "transform": {
+      "^.+\\.js$": "<rootDir>/transformer.js"
+    }
+  }
+}

e2e/global-setup-custom-transform/setup.js

@@ -0,0 +1,22 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+const crypto = require('crypto');
+const fs = require('fs');
+const {createDirectory} = require('jest-util');
+const os = require('os');
+const path = require('path');
+
+const DIR = path.join(os.tmpdir(), 'jest-global-setup-custom-transform');
+
+module.exports = function() {
+  return new Promise(resolve => {
+    createDirectory(DIR);
+    const fileId = crypto.randomBytes(20).toString('hex');
+    fs.writeFileSync(path.join(DIR, fileId), 'setup');
+    resolve();
+  });
+};

e2e/global-setup-custom-transform/transformer.js

@@ -0,0 +1,15 @@
+// Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
+
+'use strict';
+
+const fileToTransform = require.resolve('./index.js');
+
+module.exports = {
+  process(src, filename) {
+    if (filename === fileToTransform) {
+      return src.replace('hello', 'hello, world');
+    }
+
+    return src;
+  },
+};

packages/jest-cli/src/runGlobalHook.js

@@ -54,6 +54,10 @@ export default ({
 
       const transformer = new Runtime.ScriptTransformer(projectConfig);
 
+      // Load the transformer to avoid a cycle where we need to load a
+      // transformer in order to transform it in the require hooks
+      transformer.preloadTransformer(modulePath);
+
       const revertHook = addHook(
         (code, filename) =>
           transformer.transformSource(filename, code, false).code || code,

packages/jest-runtime/src/ScriptTransformer.js

@@ -204,6 +204,12 @@ export default class ScriptTransformer {
     }
   }
 
+  // We don't want to expose transformers to the outside - this function is just
+  // to warm up `this._transformCache`
+  preloadTransformer(filepath: Path): void {
+    this._getTransformer(filepath);
+  }
+
   transformSource(filepath: Path, content: string, instrument: boolean) {
     const filename = this._getRealPath(filepath);
     const transform = this._getTransformer(filename);

packages/jest-runtime/src/__tests__/script_transformer.test.js

@@ -210,7 +210,7 @@ describe('ScriptTransformer', () => {
     expect(vm.Script.mock.calls[0][0]).toMatchSnapshot();
 
     // no-cache case
-    expect(fs.readFileSync.mock.calls.length).toBe(1);
+    expect(fs.readFileSync).toHaveBeenCalledTimes(1);
     expect(fs.readFileSync).toBeCalledWith('/fruits/banana.js', 'utf8');
 
     // in-memory cache
@@ -258,7 +258,7 @@ describe('ScriptTransformer', () => {
     expect(vm.Script.mock.calls[0][0]).toContain(fsSourceCode);
 
     // Native files should never be transformed.
-    expect(shouldInstrument.mock.calls.length).toBe(0);
+    expect(shouldInstrument).toHaveBeenCalledTimes(0);
   });
 
   it(
@@ -512,7 +512,7 @@ describe('ScriptTransformer', () => {
     scriptTransformer = new ScriptTransformer(transformConfig);
     scriptTransformer.transform('/fruits/banana.js', {});
 
-    expect(fs.readFileSync.mock.calls.length).toBe(2);
+    expect(fs.readFileSync).toHaveBeenCalledTimes(2);
     expect(fs.readFileSync).toBeCalledWith('/fruits/banana.js', 'utf8');
     expect(fs.readFileSync).toBeCalledWith(cachePath, 'utf8');
     expect(writeFileAtomic.sync).not.toBeCalled();
@@ -525,7 +525,7 @@ describe('ScriptTransformer', () => {
     scriptTransformer = new ScriptTransformer(transformConfig);
     scriptTransformer.transform('/fruits/banana.js', {});
 
-    expect(fs.readFileSync.mock.calls.length).toBe(1);
+    expect(fs.readFileSync).toHaveBeenCalledTimes(1);
     expect(fs.readFileSync).toBeCalledWith('/fruits/banana.js', 'utf8');
     expect(fs.readFileSync).not.toBeCalledWith(cachePath, 'utf8');
     expect(writeFileAtomic.sync).toBeCalled();
@@ -546,7 +546,24 @@ describe('ScriptTransformer', () => {
 
     anotherScriptTransformer.transform('/fruits/banana.js', {});
 
-    expect(fs.readFileSync.mock.calls.length).toBe(2);
+    expect(fs.readFileSync).toHaveBeenCalledTimes(2);
     expect(fs.readFileSync).toBeCalledWith('/fruits/banana.js', 'utf8');
   });
+
+  it('preload transformer when using `preloadTransformer`', () => {
+    const scriptTransformer = new ScriptTransformer({
+      ...config,
+      transform: [['^.+\\.js$', 'test_preprocessor']],
+    });
+
+    expect(Array.from(scriptTransformer._transformCache.entries())).toEqual([]);
+
+    expect(
+      scriptTransformer.preloadTransformer('/fruits/banana.js'),
+    ).toBeUndefined();
+
+    expect(Array.from(scriptTransformer._transformCache.entries())).toEqual([
+      ['test_preprocessor', expect.any(Object)],
+    ]);
+  });
 });