fix: account for exports being a string (#4859)

fixes #4858

Author: schiller-manuel

packages/react-start-plugin/src/index.ts

@@ -12,6 +12,23 @@ export type {
   WithReactPlugin,
 } from './schema'
 
+function hasRootExport(
+  exportsField?: Record<string, unknown> | string,
+): boolean {
+  if (!exportsField) return false
+
+  if (typeof exportsField === 'string') {
+    // shorthand form: "exports": "./index.js"
+    return true
+  }
+
+  if (typeof exportsField === 'object') {
+    return '.' in exportsField
+  }
+
+  return false
+}
+
 export function TanStackStartVitePlugin(
   opts?: TanStackStartInputConfig & WithReactPlugin,
 ): Array<PluginOption> {
@@ -104,11 +121,7 @@ export default createStartHandler({
           if (opts.name === '@tanstack/react-router-devtools') {
             return 'exclude'
           }
-          if (
-            opts.exports &&
-            '.' in opts.exports &&
-            'react' in opts.peerDependencies
-          ) {
+          if (hasRootExport(opts.exports) && 'react' in opts.peerDependencies) {
             return 'include'
           }
           return undefined

packages/start-plugin-core/src/plugin.ts

@@ -47,7 +47,7 @@ export interface TanStackStartVitePluginCoreOptions {
   crawlPackages?: (opts: {
     name: string
     peerDependencies: Record<string, any>
-    exports?: Record<string, any>
+    exports?: Record<string, any> | string
   }) => 'include' | 'exclude' | undefined
 }
 // this needs to live outside of the TanStackStartVitePluginCore since it will be invoked multiple times by vite