Run user middleware when adding route data to pages

packages/starlight/components/StarlightPage.astro

@@ -1,4 +1,5 @@
 ---
+import { attachRouteDataAndRunMiddleware } from '../utils/routing/middleware';
 import {
 	generateStarlightPageRouteData,
 	type StarlightPageProps as Props,
@@ -7,13 +8,10 @@ import Page from './Page.astro';
 
 export type StarlightPageProps = Props;
 
-// TODO: This is a bit tricky to solve.
-// We can’t apply other middleware transformations to route data here, so that makes
-// the `<StarlightPage>` behaviour quite different from regular pages.
-Astro.locals.starlightRoute = await generateStarlightPageRouteData({
-	props: Astro.props,
-	url: Astro.url,
-});
+await attachRouteDataAndRunMiddleware(
+	Astro,
+	await generateStarlightPageRouteData({ props: Astro.props, url: Astro.url })
+);
 ---
 
 <Page><slot /></Page>

packages/starlight/locals.ts

@@ -1,9 +1,10 @@
 import { defineMiddleware } from 'astro:middleware';
-import { useTranslations } from './utils/translations';
 import { useRouteData } from './utils/routing/data';
+import { attachRouteDataAndRunMiddleware } from './utils/routing/middleware';
+import { useTranslations } from './utils/translations';
 
 export const onRequest = defineMiddleware(async (context, next) => {
 	context.locals.t = useTranslations(context.currentLocale);
-	context.locals.starlightRoute = await useRouteData(context);
+	await attachRouteDataAndRunMiddleware(context, await useRouteData(context));
 	return next();
 });

packages/starlight/utils/routing/middleware.ts

@@ -0,0 +1,19 @@
+import type { APIContext } from 'astro';
+import { klona } from 'klona/lite';
+import { routeMiddleware } from 'virtual:starlight/route-middleware';
+import type { StarlightRouteData } from './types';
+
+/**
+ * Adds a deep clone of the passed `routeData` object to locals and then runs middleware.
+ * @param context Astro context object
+ * @param routeData Initial route data object to attach.
+ */
+export async function attachRouteDataAndRunMiddleware(
+	context: APIContext,
+	routeData: StarlightRouteData
+) {
+	context.locals.starlightRoute = klona(routeData);
+	for (const middlewareFn of routeMiddleware) {
+		await middlewareFn(context);
+	}
+}