test: add a test case for issue vitejs#3040

packages/playground/resolve/__tests__/resolve.spec.ts

@@ -54,6 +54,10 @@ test('dont add extension to directory name (./dir-with-ext.js/index.js)', async
   expect(await page.textContent('.dir-with-ext')).toMatch('[success]')
 })
 
+test('a ts module can import another ts module using its corresponding js file name', async () => {
+  expect(await page.textContent('.ts-extension')).toMatch('[success]')
+})
+
 test('filename with dot', async () => {
   expect(await page.textContent('.dot')).toMatch('[success]')
 })

packages/playground/resolve/index.html

@@ -33,6 +33,11 @@ <h2>Resolve to non-duplicated file extension</h2>
 <h2>Don't add extensions to directory names</h2>
 <p class="dir-with-ext">fail</p>
 
+<h2>
+  A ts module can import another ts module using its corresponding js file name
+</h2>
+<p class="ts-extension">fail</p>
+
 <h2>Resolve file name containing dot</h2>
 <p class="dot">fail</p>
 
@@ -119,6 +124,9 @@ <h2>resolve package that contains # in path</h2>
   import { file as dirWithExtMsg } from './dir-with-ext'
   text('.dir-with-ext', dirWithExtMsg)
 
+  import { msg as tsExtensionMsg } from './ts-extension'
+  text('.ts-extension', tsExtensionMsg)
+
   // filename with dot
   import { bar } from './util/bar.util'
   text('.dot', bar())

packages/playground/resolve/ts-extension/hello.ts

@@ -0,0 +1 @@
+export const msg = '[success] use .js extension to import a ts module'

packages/playground/resolve/ts-extension/index.ts

@@ -0,0 +1,3 @@
+import { msg } from './hello.js'
+
+export { msg }

packages/playground/resolve/vite.config.js

@@ -2,7 +2,7 @@ const virtualFile = '@virtual-file'
 
 module.exports = {
   resolve: {
-    extensions: ['.mjs', '.js', '.es'],
+    extensions: ['.mjs', '.js', '.es', '.ts'],
     mainFields: ['custom', 'module'],
     conditions: ['custom']
   },