Warn when `getStaticPaths` exists without a `prerender` statement (#7713)

* wip: warning on getStaticPaths without prerender

* refactor: move getStaticPaths warning to scanner plugin

* chore: do not add to test fixture

* chore: remove legacy getStaticPaths validation

* refactor: update warning message

* chore: typo

* chore: add changeset

* chore: remove unused variables

* refactor: make settings optional

* chore: fix lint

* chore: update message to include reason

6 files changed, 35 insertions, 21 deletions

diff --git a/.changeset/sixty-plums-appear.md b/.changeset/sixty-plums-appear.md
new file mode 100644
index 000000000..3b8150ca0
--- /dev/null
+++ b/.changeset/sixty-plums-appear.md
@@ -0,0 +1,5 @@
+---
+'astro': patch
+---
+
+Update warning when `getStaticPaths` is detected but a route is not prerendered.
diff --git a/packages/astro/src/core/create-vite.ts b/packages/astro/src/core/create-vite.ts
index 279a7ffde..52b5fd277 100644
--- a/packages/astro/src/core/create-vite.ts
+++ b/packages/astro/src/core/create-vite.ts
@@ -125,7 +125,7 @@ export async function createVite(
 			mode === 'dev' && astroIntegrationsContainerPlugin({ settings, logging }),
 			astroScriptsPageSSRPlugin({ settings }),
 			astroHeadPlugin(),
-			astroScannerPlugin({ settings }),
+			astroScannerPlugin({ settings, logging }),
 			astroInjectEnvTsPlugin({ settings, logging, fs }),
 			astroContentVirtualModPlugin({ settings }),
 			astroContentImportPlugin({ fs, settings }),
diff --git a/packages/astro/src/core/render/route-cache.ts b/packages/astro/src/core/render/route-cache.ts
index 71b2966de..7ad247ef8 100644
--- a/packages/astro/src/core/render/route-cache.ts
+++ b/packages/astro/src/core/render/route-cache.ts
@@ -34,7 +34,7 @@ export async function callGetStaticPaths({
 	const cached = routeCache.get(route);
 	if (cached?.staticPaths) return cached.staticPaths;
 
-	validateDynamicRouteModule(mod, { ssr, logging, route });
+	validateDynamicRouteModule(mod, { ssr, route });
 
 	// No static paths in SSR mode. Return an empty RouteCacheEntry.
 	if (ssr && !route.prerender) {
diff --git a/packages/astro/src/core/routing/validation.ts b/packages/astro/src/core/routing/validation.ts
index 1a3bab82a..9a562c044 100644
--- a/packages/astro/src/core/routing/validation.ts
+++ b/packages/astro/src/core/routing/validation.ts
@@ -1,4 +1,3 @@
-import { bold } from 'kleur/colors';
 import type { ComponentInstance, GetStaticPathsResult, RouteData } from '../../@types/astro';
 import { AstroError, AstroErrorData } from '../errors/index.js';
 import type { LogOptions } from '../logger/core';
@@ -19,26 +18,17 @@ export function validateGetStaticPathsParameter([key, value]: [string, any], rou
 	}
 }
 
-/** Warn or error for deprecated or malformed route components */
+/** Error for deprecated or malformed route components */
 export function validateDynamicRouteModule(
 	mod: ComponentInstance,
 	{
 		ssr,
-		logging,
 		route,
 	}: {
 		ssr: boolean;
-		logging: LogOptions;
 		route: RouteData;
 	}
 ) {
-	if (ssr && mod.getStaticPaths && !route.prerender) {
-		warn(
-			logging,
-			'getStaticPaths',
-			`getStaticPaths() in ${bold(route.component)} is ignored when "output: server" is set.`
-		);
-	}
 	if ((!ssr || route.prerender) && !mod.getStaticPaths) {
 		throw new AstroError({
 			...AstroErrorData.GetStaticPathsRequired,
diff --git a/packages/astro/src/vite-plugin-scanner/index.ts b/packages/astro/src/vite-plugin-scanner/index.ts
index 465ff74ed..439a56d46 100644
--- a/packages/astro/src/vite-plugin-scanner/index.ts
+++ b/packages/astro/src/vite-plugin-scanner/index.ts
@@ -1,11 +1,20 @@
-import { normalizePath, type Plugin as VitePlugin } from 'vite';
+import type { Plugin as VitePlugin } from 'vite';
 import type { AstroSettings } from '../@types/astro.js';
-import { isEndpoint, isPage } from '../core/util.js';
+import { type LogOptions } from '../core/logger/core.js';
 
-import { getPrerenderDefault } from '../prerender/utils.js';
+import { normalizePath } from 'vite';
+import { bold } from 'kleur/colors';
+import { warn } from '../core/logger/core.js';
+import { isEndpoint, isPage, rootRelativePath } from '../core/util.js';
+import { getPrerenderDefault, isServerLikeOutput } from '../prerender/utils.js';
 import { scan } from './scan.js';
 
-export default function astroScannerPlugin({ settings }: { settings: AstroSettings }): VitePlugin {
+export interface AstroPluginScannerOptions {
+	settings: AstroSettings;
+	logging: LogOptions;
+}
+
+export default function astroScannerPlugin({ settings, logging }: AstroPluginScannerOptions): VitePlugin {
 	return {
 		name: 'astro:scanner',
 		enforce: 'post',
@@ -26,11 +35,17 @@ export default function astroScannerPlugin({ settings }: { settings: AstroSettin
 			const fileIsEndpoint = isEndpoint(fileURL, settings);
 			if (!(fileIsPage || fileIsEndpoint)) return;
 			const defaultPrerender = getPrerenderDefault(settings.config);
-			const pageOptions = await scan(code, id, settings.config.output === 'hybrid');
+			const pageOptions = await scan(code, id, settings);
 
 			if (typeof pageOptions.prerender === 'undefined') {
 				pageOptions.prerender = defaultPrerender;
 			}
+			
+			// `getStaticPaths` warning is just a string check, should be good enough for most cases
+			if (!pageOptions.prerender && isServerLikeOutput(settings.config) && code.includes('getStaticPaths')) {
+				const reason = ` because \`output: "${settings.config.output}"\` is set`
+				warn(logging, "getStaticPaths", `The getStaticPaths() statement in ${bold(rootRelativePath(settings.config.root, fileURL, true))} has been ignored${reason}.\n\nAdd \`export const prerender = true;\` to prerender this page.`);
+			}
 
 			const { meta = {} } = this.getModuleInfo(id) ?? {};
 			return {
diff --git a/packages/astro/src/vite-plugin-scanner/scan.ts b/packages/astro/src/vite-plugin-scanner/scan.ts
index 83ca3c5c5..69a0945d6 100644
--- a/packages/astro/src/vite-plugin-scanner/scan.ts
+++ b/packages/astro/src/vite-plugin-scanner/scan.ts
@@ -1,6 +1,8 @@
+import type { PageOptions } from '../vite-plugin-astro/types.js';
+import type { AstroSettings } from '../@types/astro.js';
+
 import * as eslexer from 'es-module-lexer';
 import { AstroError, AstroErrorData } from '../core/errors/index.js';
-import type { PageOptions } from '../vite-plugin-astro/types.js';
 
 const BOOLEAN_EXPORTS = new Set(['prerender']);
 
@@ -34,7 +36,7 @@ function isFalsy(value: string) {
 
 let didInit = false;
 
-export async function scan(code: string, id: string, isHybridOutput = false): Promise<PageOptions> {
+export async function scan(code: string, id: string, settings?: AstroSettings): Promise<PageOptions> {
 	if (!includesExport(code)) return {};
 	if (!didInit) {
 		await eslexer.init;
@@ -42,6 +44,7 @@ export async function scan(code: string, id: string, isHybridOutput = false): Pr
 	}
 
 	const [, exports] = eslexer.parse(code, id);
+
 	let pageOptions: PageOptions = {};
 	for (const _export of exports) {
 		const { n: name, le: endOfLocalName } = _export;
@@ -62,7 +65,7 @@ export async function scan(code: string, id: string, isHybridOutput = false): Pr
 			if (prefix !== 'const' || !(isTruthy(suffix) || isFalsy(suffix))) {
 				throw new AstroError({
 					...AstroErrorData.InvalidPrerenderExport,
-					message: AstroErrorData.InvalidPrerenderExport.message(prefix, suffix, isHybridOutput),
+					message: AstroErrorData.InvalidPrerenderExport.message(prefix, suffix, settings?.config.output === 'hybrid' ?? false),
 					location: { file: id },
 				});
 			} else {
@@ -70,5 +73,6 @@ export async function scan(code: string, id: string, isHybridOutput = false): Pr
 			}
 		}
 	}
+
 	return pageOptions;
 }