fix: prefer exports when resolving (#10371)

Co-authored-by: bluwy <bjornlu.dev@gmail.com>

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

@@ -648,13 +648,36 @@ export function tryNodeResolve(
     basedir = nestedResolveFrom(nestedRoot, basedir, preserveSymlinks)
   }
 
+  // nearest package.json
+  let nearestPkg: PackageData | undefined
+  // nearest package.json that may have the `exports` field
   let pkg: PackageData | undefined
-  const pkgId = possiblePkgIds.reverse().find((pkgId) => {
-    pkg = resolvePackageData(pkgId, basedir, preserveSymlinks, packageCache)!
-    return pkg
+
+  let pkgId = possiblePkgIds.reverse().find((pkgId) => {
+    nearestPkg = resolvePackageData(
+      pkgId,
+      basedir,
+      preserveSymlinks,
+      packageCache
+    )!
+    return nearestPkg
   })!
 
-  if (!pkg) {
+  const rootPkgId = possiblePkgIds[0]
+  const rootPkg = resolvePackageData(
+    rootPkgId,
+    basedir,
+    preserveSymlinks,
+    packageCache
+  )!
+  if (rootPkg?.data?.exports) {
+    pkg = rootPkg
+    pkgId = rootPkgId
+  } else {
+    pkg = nearestPkg
+  }
+
+  if (!pkg || !nearestPkg) {
     // if import can't be found, check if it's an optional peer dep.
     // if so, we can resolve to a special id that errors only when imported.
     if (
@@ -753,7 +776,8 @@ export function tryNodeResolve(
   }
 
   const ext = path.extname(resolved)
-  const isCJS = ext === '.cjs' || (ext === '.js' && pkg.data.type !== 'module')
+  const isCJS =
+    ext === '.cjs' || (ext === '.js' && nearestPkg.data.type !== 'module')
 
   if (
     !options.ssrOptimizeCheck &&

packages/vite/src/node/ssr/ssrModuleLoader.ts

@@ -126,7 +126,7 @@ async function instantiateModule(
     preserveSymlinks,
     isBuild: true,
     isProduction,
-    isRequire: true,
+    isRequire: false,
     root
   }
 

playground/resolve/__tests__/resolve.spec.ts

@@ -36,6 +36,13 @@ test('deep import with exports field + mapped dir', async () => {
   )
 })
 
+// this is how Svelte 3 is packaged
+test('deep import with exports and legacy fallback', async () => {
+  expect(await page.textContent('.exports-legacy-fallback')).toMatch(
+    '[success]'
+  )
+})
+
 test('Respect exports field env key priority', async () => {
   expect(await page.textContent('.exports-env')).toMatch('[success]')
 })

playground/resolve/exports-legacy-fallback/dir/index.js

@@ -0,0 +1 @@
+export const msg = '[fail] mapped js file'

playground/resolve/exports-legacy-fallback/dir/index.mjs

@@ -0,0 +1 @@
+export const msg = '[success] mapped mjs file'

playground/resolve/exports-legacy-fallback/dir/package.json

@@ -0,0 +1,4 @@
+{
+  "main": "index.js",
+  "module": "index.mjs"
+}

playground/resolve/exports-legacy-fallback/index.js

@@ -0,0 +1 @@
+export default 5

playground/resolve/exports-legacy-fallback/package.json

@@ -0,0 +1,12 @@
+{
+  "name": "resolve-exports-legacy-fallback",
+  "private": true,
+  "version": "1.0.0",
+  "exports": {
+    "./dir": {
+      "import": "./dir/index.mjs",
+      "require": "./dir/index.js"
+    },
+    ".": "index.js"
+  }
+}

playground/resolve/index.html

@@ -24,6 +24,9 @@ <h2>Deep import with exports field + mapped directory</h2>
 <h2>Exports field env priority</h2>
 <p class="exports-env">fail</p>
 
+<h2>Exports with legacy fallback</h2>
+<p class="exports-legacy-fallback">fail</p>
+
 <h2>Resolve /index.*</h2>
 <p class="index">fail</p>
 
@@ -163,6 +166,9 @@ <h2>resolve package that contains # in path</h2>
   import { msg as exportsEnvMsg } from 'resolve-exports-env'
   text('.exports-env', exportsEnvMsg)
 
+  import { msg as exportsLegacyFallbackMsg } from 'resolve-exports-legacy-fallback/dir'
+  text('.exports-legacy-fallback', exportsLegacyFallbackMsg)
+
   // implicit index resolving
   import { foo } from './util'
   text('.index', foo())

playground/resolve/package.json

@@ -20,6 +20,7 @@
     "resolve-custom-condition": "link:./custom-condition",
     "resolve-custom-main-field": "link:./custom-main-field",
     "resolve-exports-env": "link:./exports-env",
+    "resolve-exports-legacy-fallback": "link:./exports-legacy-fallback",
     "resolve-exports-path": "link:./exports-path",
     "resolve-linked": "workspace:*"
   }