prerenderConcurrency option

.changeset/big-drinks-invite.md

@@ -0,0 +1,5 @@
+---
+"@react-router/dev": patch
+---
+
+Introduce a `prerender.unstable_concurrency` option, to support running the prerendering concurrently, potentially speeding up the build.

contributors.yml

@@ -210,6 +210,7 @@
 - kigawas
 - kilavvy
 - kiliman
+- kirillgroshkov
 - kkirsche
 - kno-raziel
 - knownasilya

integration/vite-prerender-test.ts

@@ -577,6 +577,58 @@ test.describe("Prerendering", () => {
       expect(html).toMatch('<h2 data-route="true">About</h2>');
       expect(html).toMatch('<p data-loader-data="true">About Loader Data</p>');
     });
+
+    test("Permits a concurrency option", async () => {
+      fixture = await createFixture({
+        prerender: true,
+        files: {
+          ...files,
+          "react-router.config.ts": js`
+            export default {
+              prerender: {
+                paths: ['/', '/about'],
+                unstable_concurrency: 2,
+              },
+            }
+          `,
+          "vite.config.ts": js`
+            import { defineConfig } from "vite";
+            import { reactRouter } from "@react-router/dev/vite";
+
+            export default defineConfig({
+              build: { manifest: true },
+              plugins: [
+                reactRouter()
+              ],
+            });
+          `,
+        },
+      });
+      appFixture = await createAppFixture(fixture);
+
+      let clientDir = path.join(fixture.projectDir, "build", "client");
+      expect(listAllFiles(clientDir).sort()).toEqual([
+        "_root.data",
+        "about.data",
+        "about/index.html",
+        "favicon.ico",
+        "index.html",
+      ]);
+
+      let res = await fixture.requestDocument("/");
+      let html = await res.text();
+      expect(html).toMatch("<title>Index Title: Index Loader Data</title>");
+      expect(html).toMatch("<h1>Root</h1>");
+      expect(html).toMatch('<h2 data-route="true">Index</h2>');
+      expect(html).toMatch('<p data-loader-data="true">Index Loader Data</p>');
+
+      res = await fixture.requestDocument("/about");
+      html = await res.text();
+      expect(html).toMatch("<title>About Title: About Loader Data</title>");
+      expect(html).toMatch("<h1>Root</h1>");
+      expect(html).toMatch('<h2 data-route="true">About</h2>');
+      expect(html).toMatch('<p data-loader-data="true">About Loader Data</p>');
+    });
   });
 
   test.describe("ssr: true", () => {

packages/react-router-dev/config/config.ts

@@ -110,6 +110,13 @@ type BuildEndHook = (args: {
   viteConfig: Vite.ResolvedConfig;
 }) => void | Promise<void>;
 
+export type PrerenderPaths =
+  | boolean
+  | Array<string>
+  | ((args: {
+      getStaticPaths: () => string[];
+    }) => Array<string> | Promise<Array<string>>);
+
 /**
  * Config to be exported via the default export from `react-router.config.ts`.
  */
@@ -149,13 +156,19 @@ export type ReactRouterConfig = {
   /**
    * An array of URLs to prerender to HTML files at build time.  Can also be a
    * function returning an array to dynamically generate URLs.
+   *
+   * `unstable_concurrency` defaults to 1, which means "no concurrency" - fully serial execution.
+   * Setting it to a value more than 1 enables concurrent prerendering.
+   * Setting it to a value higher than one can increase the speed of the build,
+   * but may consume more resources, and send more concurrent requests to the
+   * server/CMS.
    */
   prerender?:
-    | boolean
-    | Array<string>
-    | ((args: {
-        getStaticPaths: () => string[];
-      }) => Array<string> | Promise<Array<string>>);
+    | PrerenderPaths
+    | {
+        paths: PrerenderPaths;
+        unstable_concurrency?: number;
+      };
   /**
    * An array of React Router plugin config presets to ease integration with
    * other platforms and tools.
@@ -462,17 +475,35 @@ async function resolveConfig({
     serverBundles = undefined;
   }
 
-  let isValidPrerenderConfig =
-    prerender == null ||
-    typeof prerender === "boolean" ||
-    Array.isArray(prerender) ||
-    typeof prerender === "function";
+  if (prerender) {
+    let isValidPrerenderPathsConfig = (p: unknown) =>
+      typeof p === "boolean" || typeof p === "function" || Array.isArray(p);
 
-  if (!isValidPrerenderConfig) {
-    return err(
-      "The `prerender` config must be a boolean, an array of string paths, " +
-        "or a function returning a boolean or array of string paths",
-    );
+    let isValidPrerenderConfig =
+      isValidPrerenderPathsConfig(prerender) ||
+      (typeof prerender === "object" &&
+        "paths" in prerender &&
+        isValidPrerenderPathsConfig(prerender.paths));
+
+    if (!isValidPrerenderConfig) {
+      return err(
+        "The `prerender`/`prerender.paths` config must be a boolean, an array " +
+          "of string paths, or a function returning a boolean or array of string paths.",
+      );
+    }
+
+    let isValidConcurrencyConfig =
+      typeof prerender != "object" ||
+      !("unstable_concurrency" in prerender) ||
+      (typeof prerender.unstable_concurrency === "number" &&
+        Number.isInteger(prerender.unstable_concurrency) &&
+        prerender.unstable_concurrency > 0);
+
+    if (!isValidConcurrencyConfig) {
+      return err(
+        "The `prerender.unstable_concurrency` config must be a positive integer if specified.",
+      );
+    }
   }
 
   let routeDiscovery: ResolvedReactRouterConfig["routeDiscovery"];