fix(resolve): ensure exports has precedence over mainFields (cherry pick #11234) (#11595)

Author: bluwy

packages/vite/src/node/plugins/resolve.ts

@@ -945,6 +945,8 @@ export function resolvePackageEntry(
       entryPoint = resolveExports(data, '.', options, targetWeb)
     }
 
+    const resolvedFromExports = !!entryPoint
+
     // if exports resolved to .mjs, still resolve other fields.
     // This is because .mjs files can technically import .cjs files which would
     // make them invalid for pure ESM environments - so if other module/browser
@@ -994,7 +996,9 @@ export function resolvePackageEntry(
       }
     }
 
-    if (!entryPoint || entryPoint.endsWith('.mjs')) {
+    // fallback to mainFields if still not resolved
+    // TODO: review if `.mjs` check is still needed
+    if (!resolvedFromExports && (!entryPoint || entryPoint.endsWith('.mjs'))) {
       for (const field of options.mainFields) {
         if (field === 'browser') continue // already checked above
         if (typeof data[field] === 'string') {

playground/resolve/__tests__/resolve.spec.ts

@@ -63,6 +63,10 @@ test('Respect production/development conditionals', async () => {
   )
 })
 
+test('Respect exports to take precedence over mainFields', async () => {
+  expect(await page.textContent('.exports-with-module')).toMatch('[success]')
+})
+
 test('implicit dir/index.js', async () => {
   expect(await page.textContent('.index')).toMatch('[success]')
 })

playground/resolve/exports-with-module/import.mjs

@@ -0,0 +1,2 @@
+// import.mjs should take precedence
+export const msg = '[success] exports with module (import.mjs)'

playground/resolve/exports-with-module/module.mjs

@@ -0,0 +1,2 @@
+// import.mjs should take precedence
+export const msg = '[fail] exports with module (module.mjs)'

playground/resolve/exports-with-module/package.json

@@ -0,0 +1,10 @@
+{
+  "name": "@vitejs/test-resolve-exports-with-module",
+  "private": true,
+  "version": "1.0.0",
+  "type": "commonjs",
+  "module": "./module.mjs",
+  "exports": {
+    "import": "./import.mjs"
+  }
+}

playground/resolve/index.html

@@ -33,6 +33,9 @@ <h2>Exports field read only from the root package.json</h2>
 <h2>Exports with legacy fallback</h2>
 <p class="exports-legacy-fallback">fail</p>
 
+<h2>Exports with module</h2>
+<p class="exports-with-module">fail</p>
+
 <h2>Resolve /index.*</h2>
 <p class="index">fail</p>
 
@@ -181,6 +184,9 @@ <h2>resolve package that contains # in path</h2>
   import { msg as exportsLegacyFallbackMsg } from '@vitejs/test-resolve-exports-legacy-fallback/dir'
   text('.exports-legacy-fallback', exportsLegacyFallbackMsg)
 
+  import { msg as exportsWithModule } from '@vitejs/test-resolve-exports-with-module'
+  text('.exports-with-module', exportsWithModule)
+
   // implicit index resolving
   import { foo } from './util'
   text('.index', foo())

playground/resolve/package.json

@@ -24,6 +24,7 @@
     "@vitejs/test-resolve-exports-from-root": "link:./exports-from-root",
     "@vitejs/test-resolve-exports-legacy-fallback": "link:./exports-legacy-fallback",
     "@vitejs/test-resolve-exports-path": "link:./exports-path",
+    "@vitejs/test-resolve-exports-with-module": "link:./exports-with-module",
     "@vitejs/test-resolve-linked": "workspace:*"
   }
 }