fix(rsc): reject uninitialized export in use server file

packages/plugin-rsc/src/transforms/module-export-effect.test.ts

@@ -93,6 +93,7 @@ export default async function Page() {}
     ['literal', `export const action = 1`],
     ['object', `export const action = {}`],
     ['array', `export const action = []`],
+    ['uninitialized variable', `export let action`],
   ])('rejects %s exports', async (_name, input) => {
     await expect(
       transform(input, { rejectNonAsyncFunction: true }),

packages/plugin-rsc/src/transforms/module-export-effect.ts

@@ -3,7 +3,7 @@ import type { Identifier } from 'estree'
 import MagicString from 'magic-string'
 import type { ESTree } from 'vite'
 import { scanModuleExports, type ModuleExportMeta } from './module-export-scan'
-import { validateNonAsyncFunction } from './utils'
+import { rejectNonAsyncFunction, validateNonAsyncFunction } from './utils'
 
 // TODO: Metadata, filtering, and returned reference contexts are currently
 // ported only for transformWrapExport compatibility. Remove them if no
@@ -128,8 +128,13 @@ export function transformModuleExportEffect(
             effects.push(generate({ binding, exportName, meta }))
           }
         }
-        if (validate && declarator.node.init) {
-          validateNonAsyncFunction(options, declarator.node.init)
+        if (validate) {
+          const init = declarator.node.init
+          if (init) {
+            validateNonAsyncFunction(options, init)
+          } else {
+            rejectNonAsyncFunction(options, declarator.node.start)
+          }
         }
       }
       if (effects.length > 0) {

packages/plugin-rsc/src/transforms/utils.ts

@@ -78,7 +78,6 @@ export function validateNonAsyncFunction(
   // export default function/class can be unnamed
   node: Node | ExportDefaultDeclaration['declaration'],
 ): void {
-  if (!opts.rejectNonAsyncFunction) return
   if (
     node.type === 'Literal' ||
     node.type === 'ObjectExpression' ||
@@ -90,8 +89,15 @@ export function validateNonAsyncFunction(
       node.type === 'ArrowFunctionExpression') &&
       !node.async)
   ) {
-    throw Object.assign(new Error(`unsupported non async function`), {
-      pos: node.start,
-    })
+    rejectNonAsyncFunction(opts, node.start)
+  }
+}
+
+export function rejectNonAsyncFunction(
+  opts: { rejectNonAsyncFunction?: boolean },
+  pos: number,
+): void {
+  if (opts.rejectNonAsyncFunction) {
+    throw Object.assign(new Error(`unsupported non async function`), { pos })
   }
 }