feat(ssr): resolve externalized packages with resolve.externalConditions and add module-sync to default external condition

packages/vite/src/node/constants.ts

@@ -64,7 +64,10 @@ export const DEFAULT_SERVER_CONDITIONS = Object.freeze(
   DEFAULT_CONDITIONS.filter((c) => c !== 'browser'),
 )
 
-export const DEFAULT_EXTERNAL_CONDITIONS = Object.freeze(['node'])
+export const DEFAULT_EXTERNAL_CONDITIONS = Object.freeze([
+  'node',
+  'module-sync',
+])
 
 /**
  * The browser versions that are included in the Baseline Widely Available on 2025-05-01.

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

@@ -755,7 +755,7 @@ export function tryNodeResolve(
   const resolveId = deepMatch ? resolveDeepImport : resolvePackageEntry
   const unresolvedId = deepMatch ? '.' + id.slice(pkgId.length) : id
 
-  let resolved = resolveId(unresolvedId, pkg, options)
+  let resolved = resolveId(unresolvedId, pkg, options, externalize)
   if (!resolved) {
     return
   }
@@ -895,6 +895,7 @@ export function resolvePackageEntry(
   id: string,
   { dir, data, setResolvedCache, getResolvedCache }: PackageData,
   options: InternalResolveOptions,
+  externalize?: boolean,
 ): string | undefined {
   const { file: idWithoutPostfix, postfix } = splitFileAndPostfix(id)
 
@@ -909,7 +910,13 @@ export function resolvePackageEntry(
     // resolve exports field with highest priority
     // using https://github.com/lukeed/resolve.exports
     if (data.exports) {
-      entryPoint = resolveExportsOrImports(data, '.', options, 'exports')
+      entryPoint = resolveExportsOrImports(
+        data,
+        '.',
+        options,
+        'exports',
+        externalize,
+      )
     }
 
     // fallback to mainFields if still not resolved
@@ -989,8 +996,12 @@ function resolveExportsOrImports(
   key: string,
   options: InternalResolveOptions,
   type: 'imports' | 'exports',
+  externalize?: boolean,
 ) {
-  const conditions = options.conditions.map((condition) => {
+  const rawConditions = externalize
+    ? options.externalConditions
+    : options.conditions
+  const conditions = rawConditions.map((condition) => {
     if (condition === DEV_PROD_CONDITION) {
       return options.isProduction ? 'production' : 'development'
     }
@@ -1012,6 +1023,7 @@ function resolveDeepImport(
   id: string,
   { setResolvedCache, getResolvedCache, dir, data }: PackageData,
   options: InternalResolveOptions,
+  externalize?: boolean,
 ): string | undefined {
   const cache = getResolvedCache(id, options)
   if (cache) {
@@ -1026,7 +1038,13 @@ function resolveDeepImport(
     if (isObject(exportsField) && !Array.isArray(exportsField)) {
       // resolve without postfix (see #7098)
       const { file, postfix } = splitFileAndPostfix(relativeId)
-      const exportsId = resolveExportsOrImports(data, file, options, 'exports')
+      const exportsId = resolveExportsOrImports(
+        data,
+        file,
+        options,
+        'exports',
+        externalize,
+      )
       if (exportsId !== undefined) {
         relativeId = exportsId + postfix
       } else {

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

@@ -40,7 +40,7 @@ export interface SSROptions {
     /**
      * Conditions that are used during ssr import (including `ssrLoadModule`) of externalized dependencies.
      *
-     * @default ['node']
+     * @default ['node', 'module-sync']
      */
     externalConditions?: string[]
 

playground/ssr-resolve/__tests__/ssr-resolve.spec.ts

@@ -1,6 +1,10 @@
+import { execFile } from 'node:child_process'
+import { promisify } from 'node:util'
 import { expect, test } from 'vitest'
 import { isBuild, readFile, testDir } from '~utils'
 
+const execFileAsync = promisify(execFile)
+
 test.runIf(isBuild)('correctly resolve entrypoints', async () => {
   const contents = readFile('dist/main.mjs')
 
@@ -19,11 +23,13 @@ test.runIf(isBuild)('correctly resolve entrypoints', async () => {
     new RegExp(`from ${_}@vitejs/test-deep-import/foo/index.js${_}`),
   )
 
-  expect(contents).toMatch(
-    new RegExp(`from ${_}@vitejs/test-deep-import/bar${_}`),
-  )
+  // expect(contents).toMatch(
+  //   new RegExp(`from ${_}@vitejs/test-deep-import/utils/bar.js${_}`),
+  // )
+
+  expect(contents).toMatch(new RegExp(`from ${_}@vitejs/test-module-sync${_}`))
 
-  await expect(import(`${testDir}/dist/main.mjs`)).resolves.toBeTruthy()
+  await execFileAsync('node', [`${testDir}/dist/main.mjs`])
 })
 
 test.runIf(isBuild)(

playground/ssr-resolve/main.js

@@ -5,14 +5,16 @@ import fileEntry from '@vitejs/test-entries/file'
 // has `exports` key, should resolve to pkg-exports/entry
 import pkgExportsEntry from '@vitejs/test-resolve-pkg-exports/entry'
 import deepFoo from '@vitejs/test-deep-import/foo'
-import deepBar from '@vitejs/test-deep-import/bar'
+// import deepBar from '@vitejs/test-deep-import/bar'
+import moduleSync from '@vitejs/test-module-sync'
 import { used } from './util'
 
 export default `
   entries/dir: ${dirEntry}
   entries/file: ${fileEntry}
   pkg-exports/entry: ${pkgExportsEntry}
   deep-import/foo: ${deepFoo}
-  deep-import/bar: ${deepBar}
+  ${/* `deep-import/bar: ${deepBar}` */ ''}
+  module-sync: ${moduleSync}
   util: ${used(['[success]'])}
 `

playground/ssr-resolve/package.json

@@ -8,8 +8,9 @@
     "debug": "node --inspect-brk ../../packages/vite/bin/vite build"
   },
   "dependencies": {
+    "@vitejs/test-deep-import": "file:./deep-import",
     "@vitejs/test-entries": "file:./entries",
-    "@vitejs/test-resolve-pkg-exports": "file:./pkg-exports",
-    "@vitejs/test-deep-import": "file:./deep-import"
+    "@vitejs/test-module-sync": "file:./pkg-module-sync",
+    "@vitejs/test-resolve-pkg-exports": "file:./pkg-exports"
   }
 }

playground/ssr-resolve/pkg-module-sync/index.js

@@ -0,0 +1 @@
+export default 'module-sync'

playground/ssr-resolve/pkg-module-sync/package.json

@@ -0,0 +1,11 @@
+{
+  "name": "@vitejs/test-module-sync",
+  "type": "module",
+  "private": true,
+  "version": "0.0.0",
+  "exports": {
+    ".": {
+      "module-sync": "./index.js"
+    }
+  }
+}