feat: support async createTransformer

Simply wrap the only invocation of `createTransformer` inside an await expression to support async `createTransformer`.
jestjs · Jan 12, 2023 · 9571498 · 9571498
1 parent ee63afc
commit 9571498
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Showing 4 changed files with 31 additions and 4 deletions.
diff --git a/packages/jest-transform/src/ScriptTransformer.ts b/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' &&

diff --git a/packages/jest-transform/src/__tests__/ScriptTransformer.test.ts b/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,

diff --git a/packages/jest-transform/src/types.ts b/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

diff --git a/website/versioned_docs/version-29.3/CodeTransformation.md b/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