fix: SSR deep imports externalization (fixes #8420) (#8421)

* fix: respect package.exports when resolving SSR deep imports
* fix: don't externalize .css deep imports

Author: patak-dev

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

@@ -262,7 +262,6 @@ export function resolvePlugin(baseOptions: InternalResolveOptions): Plugin {
       // bare package imports, perform node resolve
       if (bareImportRE.test(id)) {
         const external = options.shouldExternalize?.(id)
-
         if (
           !external &&
           asSrc &&
@@ -636,8 +635,17 @@ export function tryNodeResolve(
       return resolved
     }
     const resolvedExt = path.extname(resolved.id)
-    const resolvedId =
-      isDeepImport && path.extname(id) !== resolvedExt ? id + resolvedExt : id
+    let resolvedId = id
+    if (isDeepImport) {
+      // check ext before externalizing - only externalize
+      // extension-less imports and explicit .js imports
+      if (resolvedExt && !resolved.id.match(/(.js|.mjs|.cjs)$/)) {
+        return
+      }
+      if (!pkg?.data.exports && path.extname(id) !== resolvedExt) {
+        resolvedId += resolvedExt
+      }
+    }
     return { ...resolved, id: resolvedId, external: true }
   }
 

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

@@ -139,29 +139,19 @@ function createIsSsrExternal(
     isBuild: true
   }
 
-  const isPackageEntry = (id: string) => {
+  const isValidPackageEntry = (id: string) => {
     if (!bareImportRE.test(id) || id.includes('\0')) {
       return false
     }
-    if (
-      tryNodeResolve(
-        id,
-        undefined,
-        resolveOptions,
-        ssr?.target === 'webworker',
-        undefined,
-        true
-      )
-    ) {
-      return true
-    }
-    try {
-      // no main entry, but deep imports may be allowed
-      if (resolveFrom(`${id}/package.json`, root)) {
-        return true
-      }
-    } catch {}
-    return false
+    return !!tryNodeResolve(
+      id,
+      undefined,
+      resolveOptions,
+      ssr?.target === 'webworker',
+      undefined,
+      true,
+      true // try to externalize, will return undefined if not possible
+    )
   }
 
   return (id: string) => {
@@ -171,7 +161,7 @@ function createIsSsrExternal(
     const external =
       !id.startsWith('.') &&
       !path.isAbsolute(id) &&
-      (isBuiltin(id) || (isConfiguredAsExternal(id) && isPackageEntry(id)))
+      (isBuiltin(id) || (isConfiguredAsExternal(id) && isValidPackageEntry(id)))
     processedIds.set(id, external)
     return external
   }