address feedbacks

packages/jest-transform/src/ScriptTransformer.ts

@@ -26,9 +26,6 @@ import {
 } from 'jest-util';
 import handlePotentialSyntaxError from './enhanceUnexpectedTokenMessage';
 import shouldInstrument from './shouldInstrument';
-// eslint somehow complains "There should be no empty line between import groups"
-// some what similar to this: https://github.com/benmosher/eslint-plugin-import/issues/1853
-//eslint-disable-next-line import/order
 import type {
   AsyncTransformer,
   Options,
@@ -39,7 +36,6 @@ import type {
   TransformedSource,
   Transformer,
 } from './types';
-
 // Use `require` to avoid TS rootDir
 const {version: VERSION} = require('../package.json');
 
@@ -77,6 +73,7 @@ export default class ScriptTransformer {
     Config.Path,
     {transformer: Transformer; transformerConfig: unknown}
   >;
+  private readonly _transformCacheMutex: Map<Config.Path, Promise<void>>;
   private readonly _transformConfigCache: Map<Config.Path, unknown>;
 
   constructor(
@@ -86,6 +83,7 @@ export default class ScriptTransformer {
     this._config = config;
     this._cacheFS = cacheFS;
     this._transformCache = new Map();
+    this._transformCacheMutex = new Map();
     this._transformConfigCache = new Map();
 
     const configString = stableStringify(this._config);
@@ -138,7 +136,7 @@ export default class ScriptTransformer {
       this._getTransformer(filename) || {};
     let transformerCacheKey = undefined;
 
-    if (transformer && typeof transformer.getCacheKey === 'function') {
+    if (typeof transformer?.getCacheKey === 'function') {
       transformerCacheKey = transformer.getCacheKey(fileData, filename, {
         ...options,
         cacheFS: this._cacheFS,
@@ -166,26 +164,19 @@ export default class ScriptTransformer {
       (await this._getTransformerAsync(filename)) || {};
     let transformerCacheKey = undefined;
 
-    if (transformer && typeof transformer.getCacheKeyAsync === 'function') {
-      transformerCacheKey = await transformer.getCacheKeyAsync(
-        fileData,
-        filename,
-        {
+    if (transformer) {
+      const getCacheKey =
+        transformer.getCacheKeyAsync || transformer.getCacheKey;
+
+      if (typeof getCacheKey === 'function') {
+        transformerCacheKey = await getCacheKey(fileData, filename, {
           ...options,
           cacheFS: this._cacheFS,
           config: this._config,
           configString,
           transformerConfig,
-        },
-      );
-    } else if (transformer && typeof transformer.getCacheKey === 'function') {
-      transformerCacheKey = transformer.getCacheKey(fileData, filename, {
-        ...options,
-        cacheFS: this._cacheFS,
-        config: this._config,
-        configString,
-        transformerConfig,
-      });
+        });
+      }
     }
 
     return this._buildCacheKeyFromFileInfo(
@@ -259,7 +250,7 @@ export default class ScriptTransformer {
   }
 
   private async _getTransformerAsync(filename: Config.Path) {
-    if (!this._config.transform || !this._config.transform.length) {
+    if (this._config.transform.length === 0) {
       return null;
     }
 
@@ -269,12 +260,25 @@ export default class ScriptTransformer {
       return null;
     }
 
+    if (this._transformCacheMutex.has(transformPath)) {
+      await this._transformCacheMutex.get(transformPath);
+    }
+
     const cached = this._transformCache.get(transformPath);
     if (cached) {
       return cached;
     }
 
-    let transformer: AsyncTransformer = await import(transformPath);
+    let importResolve: () => void = () => {};
+    this._transformCacheMutex.set(
+      transformPath,
+      new Promise<void>(resolve => {
+        importResolve = resolve;
+      }),
+    );
+
+    let transformer: AsyncTransformer = (await import(transformPath)).default;
+    importResolve();
 
     if (!transformer) {
       throw new TypeError('Jest: a transform must export something.');
@@ -298,7 +302,7 @@ export default class ScriptTransformer {
   }
 
   private _getTransformer(filename: Config.Path) {
-    if (!this._config.transform || !this._config.transform.length) {
+    if (this._config.transform.length === 0) {
       return null;
     }
 
@@ -409,7 +413,7 @@ export default class ScriptTransformer {
         throw new TypeError(
           "Jest: a transform's `process` function must return a string, " +
             'or an object with `code` key containing this string. ' +
-            "It's `processAsync` function must return that in a promise.",
+            "It's `processAsync` function must return a Promise resolving to it.",
         );
       }
     }
@@ -496,7 +500,7 @@ export default class ScriptTransformer {
     const {transformer, transformerConfig = {}} =
       this._getTransformer(filename) || {};
     const cacheFilePath = this._getFileCachePath(filename, content, options);
-    const sourceMapPath: Config.Path | null = cacheFilePath + '.map';
+    const sourceMapPath: Config.Path = cacheFilePath + '.map';
     // Ignore cache if `config.cache` is set (--no-cache)
     const code = this._config.cache ? readCodeCacheFile(cacheFilePath) : null;
 
@@ -557,7 +561,7 @@ export default class ScriptTransformer {
       content,
       options,
     );
-    const sourceMapPath: Config.Path | null = cacheFilePath + '.map';
+    const sourceMapPath: Config.Path = cacheFilePath + '.map';
     // Ignore cache if `config.cache` is set (--no-cache)
     const code = this._config.cache ? readCodeCacheFile(cacheFilePath) : null;
 
@@ -860,9 +864,7 @@ export default class ScriptTransformer {
     const ignoreRegexp = this._cache.ignorePatternsRegExp;
     const isIgnored = ignoreRegexp ? ignoreRegexp.test(filename) : false;
 
-    return (
-      !!this._config.transform && !!this._config.transform.length && !isIgnored
-    );
+    return this._config.transform.length !== 0 && !isIgnored;
   }
 }