fix(dev): module resolution in monorepo setup (#1143)

- [x] add failing test
- [x] fix it

Author: dai-shi

e2e/fixtures/monorepo/packages/dummy-library/package.json

@@ -0,0 +1,13 @@
+{
+  "name": "dummy-library",
+  "type": "module",
+  "version": "0.0.0",
+  "description": "Dummy package for testing",
+  "exports": {
+    "./entry-point": {
+      "types": "./src/index.d.ts",
+      "import": "./src/index.js"
+    }
+  },
+  "private": true
+}

e2e/fixtures/monorepo/packages/dummy-library/src/client.js

@@ -0,0 +1,5 @@
+'use client';
+
+export function Hello() {
+  return 'hello';
+}

e2e/fixtures/monorepo/packages/dummy-library/src/index.d.ts

@@ -0,0 +1 @@
+export declare function Hello(): string;

e2e/fixtures/monorepo/packages/dummy-library/src/index.js

@@ -0,0 +1,3 @@
+// Do not add '.js' extension to reproduce the issue
+// https://github.com/dai-shi/waku/pull/1143
+export * from './client';

e2e/fixtures/monorepo/packages/waku-project/package.json

@@ -9,6 +9,7 @@
     "start": "waku start"
   },
   "dependencies": {
+    "dummy-library": "0.0.0",
     "react": "19.0.0",
     "react-dom": "19.0.0",
     "react-server-dom-webpack": "19.0.0"

e2e/fixtures/monorepo/packages/waku-project/src/pages/index.tsx

@@ -1,4 +1,7 @@
 import { Link } from 'waku';
+// @ts-expect-error no types
+// eslint-disable-next-line import/no-unresolved
+import { Hello } from 'dummy-library/entry-point';
 
 import { Counter } from '../components/counter';
 
@@ -11,6 +14,7 @@ export default async function HomePage() {
       <h1 className="text-4xl font-bold tracking-tight" data-testid="header">
         {data.headline}
       </h1>
+      <Hello />
       <p>{data.body}</p>
       <Counter />
       <Link to="/about" className="mt-4 inline-block underline">

packages/waku/src/lib/plugins/vite-plugin-rsc-transform.ts

@@ -695,6 +695,10 @@ export function rscTransformPlugin(
         return (await this.resolve(id.slice('/@id/'.length), importer, options))
           ?.id;
       }
+      if (id.startsWith('/@fs/')) {
+        return (await this.resolve(id.slice('/@fs'.length), importer, options))
+          ?.id;
+      }
       const resolved = await this.resolve(id, importer, options);
       let srcId =
         importer && (id.startsWith('./') || id.startsWith('../'))