Fix virtual module type to properly handle optional properties

The virtual module `virtual:react-router/server-build` now deliberately
implements CommonJS `export =` syntax to correctly support optional
properties in the `ServerBuild` type, ensuring proper TypeScript
compatibility with `exactOptionalPropertyTypes`.

Signed-off-by: Sora Morimoto <sora@morimoto.io>

Author: smorimoto

.changeset/tiny-gifts-wash.md

@@ -0,0 +1,7 @@
+---
+"@react-router/dev": patch
+---
+
+Fix virtual module type to properly handle optional properties.
+
+The virtual module `virtual:react-router/server-build` now deliberately implements CommonJS `export =` syntax to correctly support optional properties in the `ServerBuild` type, ensuring proper TypeScript compatibility with `exactOptionalPropertyTypes`.

integration/typegen-test.ts

@@ -490,6 +490,31 @@ test.describe("typegen", () => {
       expect(proc.status).toBe(0);
     });
 
+
+    test("works with tsconfig 'exactOptionalPropertyTypes' set to 'true'", async () => {
+      const cwd = await createProject({
+        "vite.config.ts": viteConfig,
+        "app/routes.ts": tsx`
+          import { type RouteConfig } from "@react-router/dev/routes";
+          export default [] satisfies RouteConfig;
+        `,
+        "app/handler.ts": tsx`
+          import { createRequestHandler } from "react-router";
+          import * as serverBuild from "virtual:react-router/server-build";
+          export default createRequestHandler(serverBuild);
+        `,
+      });
+
+      const tsconfig = await fse.readJson(path.join(cwd, "tsconfig.json"));
+      tsconfig.compilerOptions.exactOptionalPropertyTypes = true;
+      await fse.writeJson(path.join(cwd, "tsconfig.json"), tsconfig);
+
+      const proc = typecheck(cwd);
+      expect(proc.stdout.toString()).toBe("");
+      expect(proc.stderr.toString()).toBe("");
+      expect(proc.status).toBe(0);
+    });
+
     test("dynamic import matches 'createRequestHandler' function argument type", async () => {
       const cwd = await createProject({
         "vite.config.ts": viteConfig,

packages/react-router-dev/typegen/index.ts

@@ -152,17 +152,20 @@ function register(ctx: Context) {
 
 const virtual = ts`
   declare module "virtual:react-router/server-build" {
-    import { ServerBuild } from "react-router";
-    export const assets: ServerBuild["assets"];
-    export const assetsBuildDirectory: ServerBuild["assetsBuildDirectory"];
-    export const basename: ServerBuild["basename"];
-    export const entry: ServerBuild["entry"];
-    export const future: ServerBuild["future"];
-    export const isSpaMode: ServerBuild["isSpaMode"];
-    export const prerender: ServerBuild["prerender"];
-    export const publicPath: ServerBuild["publicPath"];
-    export const routes: ServerBuild["routes"];
-    export const ssr: ServerBuild["ssr"];
-    export const unstable_getCriticalCss: ServerBuild["unstable_getCriticalCss"];
+    import type { ServerBuild } from "react-router";
+    /**
+     * Whilst this uses the CommonJS 'export =' syntax, which is technically not
+     * ESM-compliant, it is intentionally implemented this way to properly support
+     * optional properties in the ServerBuild type.
+     *
+     * TypeScript's type system does not provide an elegant solution for defining
+     * optional exports at the module level in ESM syntax, so this approach offers
+     * the most accurate type definitions for maintainability.
+     *
+     * This ensures all properties of ServerBuild, including optional ones, are
+     * properly type-checked when using this module.
+     */
+    const serverBuild: ServerBuild;
+    export = serverBuild;
   }
 `;