feat: support async createTransformer

Simply wrap the only invocation of `createTransformer` inside an await 
expression to support async `createTransformer`.

Had to modify some tests in `babel-jest` to comply with the new return 
type of `createTransformer`.

CHANGELOG.md

@@ -9,6 +9,7 @@
 - `[jest-resolve]` Support subpath imports ([#13705](https://github.com/facebook/jest/pull/13705), [#13723](https://github.com/facebook/jest/pull/13723))
 - `[jest-runtime]` Add `jest.isolateModulesAsync` for scoped module initialization of asynchronous functions ([#13680](https://github.com/facebook/jest/pull/13680))
 - `[jest-test-result]` Added `skipped` and `focused` status to `FormattedTestResult` ([#13700](https://github.com/facebook/jest/pull/13700))
+- `[jest-transform]` Support for asynchronous `createTransformer` ([#13762](https://github.com/facebook/jest/pull/13762))
 
 ### Fixes
 

packages/babel-jest/src/__tests__/getCacheKey.test.ts

@@ -9,7 +9,7 @@ import type {TransformOptions as BabelTransformOptions} from '@babel/core';
 import type {TransformOptions} from '@jest/transform';
 import babelJest from '../index';
 
-const {getCacheKey} = babelJest.createTransformer();
+const {getCacheKey} = await babelJest.createTransformer();
 
 const processVersion = process.version;
 const nodeEnv = process.env.NODE_ENV;
@@ -47,15 +47,15 @@ describe('getCacheKey', () => {
     expect(oldCacheKey).toHaveLength(32);
   });
 
-  test('if `THIS_FILE` value is changing', () => {
+  test('if `THIS_FILE` value is changing', async () => {
     jest.doMock('graceful-fs', () => ({
       readFileSync: () => 'new this file',
     }));
 
     const {createTransformer} =
       require('../index') as typeof import('../index');
 
-    const newCacheKey = createTransformer().getCacheKey!(
+    const newCacheKey = (await createTransformer()).getCacheKey!(
       sourceText,
       sourcePath,
       transformOptions,
@@ -64,7 +64,7 @@ describe('getCacheKey', () => {
     expect(oldCacheKey).not.toEqual(newCacheKey);
   });
 
-  test('if `babelOptions.options` value is changing', () => {
+  test('if `babelOptions.options` value is changing', async () => {
     jest.doMock('../loadBabelConfig', () => {
       const babel = require('@babel/core') as typeof import('@babel/core');
 
@@ -79,7 +79,7 @@ describe('getCacheKey', () => {
     const {createTransformer} =
       require('../index') as typeof import('../index');
 
-    const newCacheKey = createTransformer().getCacheKey!(
+    const newCacheKey = (await createTransformer()).getCacheKey!(
       sourceText,
       sourcePath,
       transformOptions,
@@ -117,7 +117,7 @@ describe('getCacheKey', () => {
     expect(oldCacheKey).not.toEqual(newCacheKey);
   });
 
-  test('if `babelOptions.config` value is changing', () => {
+  test('if `babelOptions.config` value is changing', async () => {
     jest.doMock('../loadBabelConfig', () => {
       const babel = require('@babel/core') as typeof import('@babel/core');
 
@@ -132,7 +132,7 @@ describe('getCacheKey', () => {
     const {createTransformer} =
       require('../index') as typeof import('../index');
 
-    const newCacheKey = createTransformer().getCacheKey!(
+    const newCacheKey = (await createTransformer()).getCacheKey!(
       sourceText,
       sourcePath,
       transformOptions,
@@ -141,7 +141,7 @@ describe('getCacheKey', () => {
     expect(oldCacheKey).not.toEqual(newCacheKey);
   });
 
-  test('if `babelOptions.babelrc` value is changing', () => {
+  test('if `babelOptions.babelrc` value is changing', async () => {
     jest.doMock('../loadBabelConfig', () => {
       const babel = require('@babel/core') as typeof import('@babel/core');
 
@@ -156,7 +156,7 @@ describe('getCacheKey', () => {
     const {createTransformer} =
       require('../index') as typeof import('../index');
 
-    const newCacheKey = createTransformer().getCacheKey!(
+    const newCacheKey = (await createTransformer()).getCacheKey!(
       sourceText,
       sourcePath,
       transformOptions,

packages/babel-jest/src/__tests__/index.ts

@@ -28,7 +28,7 @@ jest.mock('../loadBabelConfig', () => {
   };
 });
 
-const defaultBabelJestTransformer = babelJest.createTransformer();
+const defaultBabelJestTransformer = await babelJest.createTransformer();
 
 //Mock data for all the tests
 const sourceString = `
@@ -163,8 +163,8 @@ describe('caller option correctly merges from defaults and options', () => {
   });
 });
 
-test('can pass null to createTransformer', () => {
-  const transformer = createTransformer();
+test('can pass null to createTransformer', async () => {
+  const transformer = await createTransformer();
   transformer.process(sourceString, 'dummy_path.js', {
     cacheFS: new Map<string, string>(),
     config: makeProjectConfig(),

packages/jest-transform/src/ScriptTransformer.ts

@@ -269,7 +269,9 @@ class ScriptTransformer {
             throw new Error(makeInvalidTransformerError(transformPath));
           }
           if (isTransformerFactory(transformer)) {
-            transformer = transformer.createTransformer(transformerConfig);
+            transformer = await transformer.createTransformer(
+              transformerConfig,
+            );
           }
           if (
             typeof transformer.process !== 'function' &&

packages/jest-transform/src/__tests__/ScriptTransformer.test.ts

@@ -234,6 +234,16 @@ jest.mock(
   {virtual: true},
 );
 
+jest.mock(
+  'async-factory',
+  () => ({
+    async createTransformer() {
+      return {process: jest.fn().mockReturnValue({code: 'code'})};
+    },
+  }),
+  {virtual: true},
+);
+
 jest.mock(
   'factory-for-async-preprocessor',
   () => {
@@ -551,6 +561,21 @@ describe('ScriptTransformer', () => {
     ).toBeDefined();
   });
 
+  it('handle async createTransformer', async () => {
+    config = {
+      ...config,
+      transform: [['\\.js$', 'async-factory', {}]],
+    };
+    const scriptTransformer = await createScriptTransformer(config);
+    expect(
+      await scriptTransformer.transformSourceAsync(
+        'sample.js',
+        '',
+        getTransformOptions(false),
+      ),
+    ).toBeDefined();
+  });
+
   it('throws an error if createTransformer returns object without `process` method', async () => {
     config = {
       ...config,

packages/jest-transform/src/types.ts

@@ -149,7 +149,7 @@ export type Transformer<TransformerConfig = unknown> =
 export type TransformerCreator<
   X extends Transformer<TransformerConfig>,
   TransformerConfig = unknown,
-> = (transformerConfig?: TransformerConfig) => X;
+> = (transformerConfig?: TransformerConfig) => X | Promise<X>;
 
 /**
  * Instead of having your custom transformer implement the Transformer interface

website/versioned_docs/version-29.3/CodeTransformation.md

@@ -125,7 +125,7 @@ type Transformer<TransformerConfig = unknown> =
 type TransformerCreator<
   X extends Transformer<TransformerConfig>,
   TransformerConfig = unknown,
-> = (transformerConfig?: TransformerConfig) => X;
+> = (transformerConfig?: TransformerConfig) => X | Promise<X>;
 
 type TransformerFactory<X extends Transformer> = {
   createTransformer: TransformerCreator<X>;
@@ -146,7 +146,7 @@ Semi-related to this are the supports flags we pass (see `CallerTransformOptions
 
 Though not required, we _highly recommend_ implementing `getCacheKey` as well, so we do not waste resources transpiling when we could have read its previous result from disk. You can use [`@jest/create-cache-key-function`](https://www.npmjs.com/package/@jest/create-cache-key-function) to help implement it.
 
-Instead of having your custom transformer implement the `Transformer` interface directly, you can choose to export `createTransformer`, a factory function to dynamically create transformers. This is to allow having a transformer config in your jest config.
+Instead of having your custom transformer implement the `Transformer` interface directly, you can choose to export `createTransformer`, a possibly asynchronous factory function to dynamically create transformers. This is to allow having a transformer config in your jest config.
 
 :::note