Make TransformerCreator generic to know if sync or async

jestjs · Feb 17, 2022 · 45f940e · 45f940e
1 parent cc7ff8c
commit 45f940e
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Showing 4 changed files with 15 additions and 15 deletions.
diff --git a/packages/babel-jest/src/index.ts b/packages/babel-jest/src/index.ts
@@ -148,6 +148,7 @@ async function loadBabelOptionsAsync(
 }
 
 export const createTransformer: TransformerCreator<
+  SyncTransformer<TransformOptions>,
   TransformOptions
 > = userOptions => {
   const inputOptions = userOptions ?? {};
@@ -270,11 +271,6 @@ export const createTransformer: TransformerCreator<
   };
 };
 
-const transformer: SyncTransformer<TransformOptions> = {
-  ...createTransformer(),
-  // Assigned here so only the exported transformer has `createTransformer`,
-  // instead of all created transformers by the function
-  createTransformer,
-};
+const transformer: SyncTransformer<TransformOptions> = createTransformer();
 
 export default transformer;
diff --git a/packages/jest-transform/src/ScriptTransformer.ts b/packages/jest-transform/src/ScriptTransformer.ts
@@ -74,10 +74,10 @@ async function waitForPromiseWithCleanup(
 }
 
 // type predicate
-function isTransformerFactory(
-  t: Transformer | TransformerFactory,
-): t is TransformerFactory {
-  return typeof (t as TransformerFactory).createTransformer === 'function';
+function isTransformerFactory<X extends Transformer>(
+  t: Transformer | TransformerFactory<X>,
+): t is TransformerFactory<X> {
+  return typeof (t as TransformerFactory<X>).createTransformer === 'function';
 }
 
 class ScriptTransformer {
@@ -267,7 +267,7 @@ class ScriptTransformer {
     await Promise.all(
       this._config.transform.map(
         async ([, transformPath, transformerConfig]) => {
-          let transformer: Transformer | TransformerFactory =
+          let transformer: Transformer | TransformerFactory<Transformer> =
             await requireOrImportModule(transformPath);
 
           if (!transformer) {

diff --git a/packages/jest-transform/src/index.ts b/packages/jest-transform/src/index.ts
@@ -18,6 +18,7 @@ export type {
   AsyncTransformer,
   ShouldInstrumentOptions,
   Options as TransformationOptions,
+  TransformerCreator,
   TransformOptions,
   TransformResult,
   TransformedSource,

diff --git a/packages/jest-transform/src/types.ts b/packages/jest-transform/src/types.ts
@@ -146,13 +146,16 @@ export type Transformer<OptionType = unknown> =
   | SyncTransformer<OptionType>
   | AsyncTransformer<OptionType>;
 
-export type TransformerCreator<OptionType = unknown> = (
-  options?: OptionType,
-) => Transformer<OptionType>;
+export type TransformerCreator<
+  X extends Transformer<OptionType>,
+  OptionType = unknown,
+> = (options?: OptionType) => X;
 
 /**
  * Instead of having your custom transformer implement the Transformer interface
  * directly, you can choose to export a factory function to dynamically create
  * transformers. This is to allow having a transformer config in your jest config.
  */
-export type TransformerFactory = {createTransformer: TransformerCreator};
+export type TransformerFactory<X extends Transformer> = {
+  createTransformer: TransformerCreator<X>;
+};