From 79d87a663478530d394977419d2e38a01116a4b9 Mon Sep 17 00:00:00 2001
From: Simen Bekkhus <sbekkhus91@gmail.com>
Date: Wed, 22 Apr 2020 09:25:19 +0200
Subject: [PATCH] fix(esm): handle parallel imports

---
 CHANGELOG.md                                    |  1 +
 .../__snapshots__/nativeEsm.test.ts.snap        |  2 +-
 e2e/native-esm/__tests__/native-esm.test.js     | 10 ++++++++++
 e2e/native-esm/anotherDynamicImport.js          |  8 ++++++++
 packages/jest-runtime/src/index.ts              | 17 +++++++++++------
 5 files changed, 31 insertions(+), 7 deletions(-)
 create mode 100644 e2e/native-esm/anotherDynamicImport.js

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 02728ab400e6..4a9a97423f9f 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,7 @@
 ### Fixes
 
 - `[jest-runtime]` Support importing CJS from ESM using `import` statements ([#9850](https://github.com/facebook/jest/pull/9850))
+- `[jest-runtime]` Support importing parallel dynamic `import`s
 
 ### Chore & Maintenance
 
diff --git a/e2e/__tests__/__snapshots__/nativeEsm.test.ts.snap b/e2e/__tests__/__snapshots__/nativeEsm.test.ts.snap
index be56a4394e76..ca20b5785769 100644
--- a/e2e/__tests__/__snapshots__/nativeEsm.test.ts.snap
+++ b/e2e/__tests__/__snapshots__/nativeEsm.test.ts.snap
@@ -2,7 +2,7 @@
 
 exports[`on node >=12.16.0 runs test with native ESM 1`] = `
 Test Suites: 1 passed, 1 total
-Tests:       9 passed, 9 total
+Tests:       10 passed, 10 total
 Snapshots:   0 total
 Time:        <<REPLACED>>
 Ran all test suites.
diff --git a/e2e/native-esm/__tests__/native-esm.test.js b/e2e/native-esm/__tests__/native-esm.test.js
index 8f1800e57c12..f21670b89b86 100644
--- a/e2e/native-esm/__tests__/native-esm.test.js
+++ b/e2e/native-esm/__tests__/native-esm.test.js
@@ -90,3 +90,13 @@ test('handle unlinked dynamic imports', async () => {
 
   expect(deepDouble(4)).toBe(8);
 });
+
+test('handle dynamic imports of the same module in parallel', async () => {
+  const [{double: first}, {double: second}] = await Promise.all([
+    import('../anotherDynamicImport.js'),
+    import('../anotherDynamicImport.js'),
+  ]);
+
+  expect(first).toBe(second);
+  expect(first(2)).toBe(4);
+});
diff --git a/e2e/native-esm/anotherDynamicImport.js b/e2e/native-esm/anotherDynamicImport.js
new file mode 100644
index 000000000000..84b87a513c85
--- /dev/null
+++ b/e2e/native-esm/anotherDynamicImport.js
@@ -0,0 +1,8 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+export * from './index';
diff --git a/packages/jest-runtime/src/index.ts b/packages/jest-runtime/src/index.ts
index 001de2f98ec9..6d3a81c53240 100644
--- a/packages/jest-runtime/src/index.ts
+++ b/packages/jest-runtime/src/index.ts
@@ -133,7 +133,7 @@ class Runtime {
   private _moduleMocker: typeof jestMock;
   private _isolatedModuleRegistry: ModuleRegistry | null;
   private _moduleRegistry: ModuleRegistry;
-  private _esmoduleRegistry: Map<string, VMModule>;
+  private _esmoduleRegistry: Map<string, Promise<VMModule>>;
   private _needsCoverageMapped: Set<string>;
   private _resolver: Resolver;
   private _shouldAutoMock: boolean;
@@ -357,11 +357,16 @@ class Runtime {
         },
       });
 
-      this._esmoduleRegistry.set(cacheKey, module);
-
-      await module.link(this.linkModules.bind(this));
-
-      await module.evaluate();
+      this._esmoduleRegistry.set(
+        cacheKey,
+        // we wanna put the linking promise in the cache so modules loaded in
+        // parallel can all await it. We then await it synchronously below, so
+        // we shouldn't get any unhandled rejections
+        module
+          .link(this.linkModules.bind(this))
+          .then(() => module.evaluate())
+          .then(() => module),
+      );
     }
 
     const module = this._esmoduleRegistry.get(cacheKey);