From c1024ec7f4af917ce69ce90442d3db29ca5804b5 Mon Sep 17 00:00:00 2001
From: Gen Hames <hamesg@tutanota.de>
Date: Wed, 1 Jul 2020 13:19:25 -0700
Subject: [PATCH] Add test for TS imports that use JS extensions (#480)

---
 packages/node-resolve/package.json            |  1 +
 packages/node-resolve/src/index.js            |  4 ++--
 .../extensions/import-ts-with-js-extension.ts |  4 ++++
 .../test/fixtures/extensions/main.ts          | 11 +++++++++++
 packages/node-resolve/test/test.js            | 19 +++++++++++++++++++
 5 files changed, 37 insertions(+), 2 deletions(-)
 create mode 100644 packages/node-resolve/test/fixtures/extensions/import-ts-with-js-extension.ts
 create mode 100644 packages/node-resolve/test/fixtures/extensions/main.ts

diff --git a/packages/node-resolve/package.json b/packages/node-resolve/package.json
index 1c0e9c2e0..b2492c960 100755
--- a/packages/node-resolve/package.json
+++ b/packages/node-resolve/package.json
@@ -58,6 +58,7 @@
   },
   "devDependencies": {
     "@babel/core": "^7.9.0",
+    "@babel/plugin-transform-typescript": "^7.10.4",
     "@babel/preset-env": "^7.9.0",
     "@rollup/plugin-babel": "^5.0.4",
     "@rollup/plugin-commonjs": "^13.0.0",
diff --git a/packages/node-resolve/src/index.js b/packages/node-resolve/src/index.js
index 29a7cd07c..5465b38bc 100644
--- a/packages/node-resolve/src/index.js
+++ b/packages/node-resolve/src/index.js
@@ -190,12 +190,12 @@ export function nodeResolve(opts = {}) {
         // the built-in's name.
         importSpecifierList.push(`${importee}/`);
       }
-      
+
       // TypeScript files may import '.js' to refer to either '.ts' or '.tsx'
       if (importer && importee.endsWith('.js')) {
         for (const ext of ['.ts', '.tsx']) {
           if (importer.endsWith(ext) && extensions.includes(ext)) {
-            importSpecifierList.push(importee.replace(/.js$/, ext))
+            importSpecifierList.push(importee.replace(/.js$/, ext));
           }
         }
       }
diff --git a/packages/node-resolve/test/fixtures/extensions/import-ts-with-js-extension.ts b/packages/node-resolve/test/fixtures/extensions/import-ts-with-js-extension.ts
new file mode 100644
index 000000000..95c52eab8
--- /dev/null
+++ b/packages/node-resolve/test/fixtures/extensions/import-ts-with-js-extension.ts
@@ -0,0 +1,4 @@
+import { main } from './main.js';
+// This resolves as main.ts and _not_ main.js, despite the extension
+const mainResult = main();
+export default mainResult;
diff --git a/packages/node-resolve/test/fixtures/extensions/main.ts b/packages/node-resolve/test/fixtures/extensions/main.ts
new file mode 100644
index 000000000..60668791d
--- /dev/null
+++ b/packages/node-resolve/test/fixtures/extensions/main.ts
@@ -0,0 +1,11 @@
+// To make this very clearly TypeScript and not just JS with a TS extension
+type TestType = string | string[];
+interface Main {
+  (): string;
+  propertyCall(input?: TestType): TestType;
+}
+
+const main: Main = () => 'It works!';
+main.propertyCall = () => '';
+
+export { main };
diff --git a/packages/node-resolve/test/test.js b/packages/node-resolve/test/test.js
index 574f69f2a..35da582ea 100755
--- a/packages/node-resolve/test/test.js
+++ b/packages/node-resolve/test/test.js
@@ -105,6 +105,25 @@ test('supports non-standard extensions', async (t) => {
   await testBundle(t, bundle);
 });
 
+test('supports JS extensions in TS when referring to TS imports', async (t) => {
+  const bundle = await rollup({
+    input: 'extensions/import-ts-with-js-extension.ts',
+    onwarn: () => t.fail('No warnings were expected'),
+    plugins: [
+      nodeResolve({
+        extensions: ['.js', '.ts']
+      }),
+      babel({
+        babelHelpers: 'bundled',
+        plugins: ['@babel/plugin-transform-typescript'],
+        extensions: ['.js', '.ts']
+      })
+    ]
+  });
+  const { module } = await testBundle(t, bundle);
+  t.is(module.exports, 'It works!');
+});
+
 test('ignores IDs with null character', async (t) => {
   const result = await nodeResolve().resolveId('\0someid', 'test.js');
   t.is(result, null);