fix(rsc): ensure trailing slash of BASE_URL (#589)

Author: hi-ogawa

packages/plugin-rsc/src/browser.ts

@@ -10,7 +10,9 @@ function initialize(): void {
     load: async (id) => {
       if (!import.meta.env.__vite_rsc_build__) {
         // @ts-ignore
-        return __vite_rsc_raw_import__(import.meta.env.BASE_URL + id.slice(1))
+        return __vite_rsc_raw_import__(
+          withTrailingSlash(import.meta.env.BASE_URL) + id.slice(1),
+        )
       } else {
         const import_ = clientReferences.default[id]
         if (!import_) {
@@ -21,3 +23,12 @@ function initialize(): void {
     },
   })
 }
+
+// Vite normalizes `config.base` to have trailing slash, but not for `import.meta.env.BASE_URL`.
+// https://github.com/vitejs/vite/blob/27a192fc95036dbdb6e615a4201b858eb64aa075/packages/vite/src/shared/utils.ts#L48-L53
+function withTrailingSlash(path: string): string {
+  if (path[path.length - 1] !== '/') {
+    return `${path}/`
+  }
+  return path
+}