refactor: Extract transform code to @jest-transform

CHANGELOG.md

@@ -17,6 +17,7 @@
 - `[jest-validate]` Allow `maxWorkers` as part of the `jest.config.js` ([#8565](https://github.com/facebook/jest/pull/8565))
 - `[jest-runtime]` Allow passing configuration objects to transformers ([#7288](https://github.com/facebook/jest/pull/7288))
 - `[@jest/core, @jest/test-sequencer]` Support async sort in custom `testSequencer` ([#8642](https://github.com/facebook/jest/pull/8642))
+- `[@jest-transform]` Extract transforming require logic within `jest-core` into `@jest-transform` ([#8756](https://github.com/facebook/jest/pull/8756))
 
 ### Fixes
 

packages/jest-core/package.json

@@ -29,7 +29,6 @@
     "jest-watcher": "^24.8.0",
     "micromatch": "^3.1.10",
     "p-each-series": "^1.0.0",
-    "pirates": "^4.0.1",
     "realpath-native": "^1.1.0",
     "rimraf": "^2.5.4",
     "slash": "^2.0.0",

packages/jest-core/src/runGlobalHook.ts

@@ -5,9 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-import {extname} from 'path';
 import pEachSeries from 'p-each-series';
-import {addHook} from 'pirates';
 import {Config} from '@jest/types';
 import {Test} from 'jest-runner';
 import {ScriptTransformer} from '@jest/transform';
@@ -47,46 +45,17 @@ export default async ({
 
       const transformer = new 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);
+      await transformer.requireAndTranspileModule(modulePath, async m => {
+        const globalModule = interopRequireDefault(m).default;
 
-      let transforming = false;
-      const revertHook = addHook(
-        (code, filename) => {
-          try {
-            transforming = true;
-            return (
-              transformer.transformSource(filename, code, false).code || code
-            );
-          } finally {
-            transforming = false;
-          }
-        },
-        {
-          exts: [extname(modulePath)],
-          ignoreNodeModules: false,
-          matcher: (...args) => {
-            if (transforming) {
-              // Don't transform any dependency required by the transformer itself
-              return false;
-            }
-            return transformer.shouldTransform(...args);
-          },
-        },
-      );
-
-      const globalModule = interopRequireDefault(require(modulePath)).default;
-
-      if (typeof globalModule !== 'function') {
-        throw new TypeError(
-          `${moduleName} file must export a function at ${modulePath}`,
-        );
-      }
-
-      await globalModule(globalConfig);
+        if (typeof globalModule !== 'function') {
+          throw new TypeError(
+            `${moduleName} file must export a function at ${modulePath}`,
+          );
+        }
 
-      revertHook();
+        await globalModule(globalConfig);
+      });
     });
   }
 

packages/jest-transform/package.json

@@ -20,6 +20,7 @@
     "jest-regex-util": "^24.3.0",
     "jest-util": "^24.8.0",
     "micromatch": "^3.1.10",
+    "pirates": "^4.0.1",
     "realpath-native": "^1.1.0",
     "slash": "^2.0.0",
     "source-map": "^0.6.1",

packages/jest-transform/src/ScriptTransformer.ts

@@ -20,6 +20,7 @@ import stableStringify from 'fast-json-stable-stringify';
 import slash from 'slash';
 import writeFileAtomic from 'write-file-atomic';
 import {sync as realpath} from 'realpath-native';
+import {addHook} from 'pirates';
 import {
   Options,
   Transformer,
@@ -434,6 +435,49 @@ export default class ScriptTransformer {
     return fileSource;
   }
 
+  async requireAndTranspileModule<ModuleType = unknown>(
+    moduleName: string,
+    callback?: (module: ModuleType) => void | Promise<void>,
+  ): Promise<ModuleType> {
+    // Load the transformer to avoid a cycle where we need to load a
+    // transformer in order to transform it in the require hooks
+    this.preloadTransformer(moduleName);
+
+    let transforming = false;
+    const revertHook = addHook(
+      (code, filename) => {
+        try {
+          transforming = true;
+          return this.transformSource(filename, code, false).code || code;
+        } finally {
+          transforming = false;
+        }
+      },
+      {
+        exts: [path.extname(moduleName)],
+        ignoreNodeModules: false,
+        matcher: filename => {
+          if (transforming) {
+            // Don't transform any dependency required by the transformer itself
+            return false;
+          }
+          return this.shouldTransform(filename);
+        },
+      },
+    );
+    const module: ModuleType = require(moduleName);
+
+    try {
+      if (callback) {
+        await callback(module);
+      }
+    } finally {
+      revertHook();
+    }
+
+    return module;
+  }
+
   /**
    * @deprecated use `this.shouldTransform` instead
    */