fix: Allow #top and the empty string as special-case non-missing IDs

packages/kit/src/core/postbuild/prerender.js

@@ -16,6 +16,12 @@ import { createReadableStream } from '@sveltejs/kit/node';
 
 export default forked(import.meta.url, prerender);
 
+// https://html.spec.whatwg.org/multipage/browsing-the-web.html#scrolling-to-a-fragment
+// "If fragment is the empty string, then return the special value top of the document."
+// ...and
+// "If decodedFragment is an ASCII case-insensitive match for the string 'top', then return the top of the document."
+const SPECIAL_HASHLINKS = new Set(['', 'top']);
+
 /**
  * @param {{
  *   out: string;
@@ -485,7 +491,7 @@ async function prerender({ out, manifest_path, metadata, verbose, env }) {
 		// ignore fragment links to pages that were not prerendered
 		if (!hashlinks) continue;
 
-		if (!hashlinks.includes(id)) {
+		if (!hashlinks.includes(id) && !SPECIAL_HASHLINKS.has(id)) {
 			handle_missing_id({ id, path, referrers: Array.from(referrers) });
 		}
 	}

packages/kit/test/prerendering/basics/.gitignore

@@ -1 +1,3 @@
-!.env
+!.env
+
+missing_ids

packages/kit/test/prerendering/basics/globalSetup.js

@@ -0,0 +1,5 @@
+import { execSync } from 'node:child_process';
+
+export default function setup() {
+	execSync('svelte-kit sync && pnpm run build');
+}

packages/kit/test/prerendering/basics/package.json

@@ -4,10 +4,10 @@
 	"version": "0.0.2-next.0",
 	"scripts": {
 		"dev": "vite dev",
-		"build": "vite build",
+		"build": "rm -rf ./missing_ids && mkdir ./missing_ids && vite build",
 		"preview": "vite preview",
 		"check": "svelte-kit sync && tsc && svelte-check",
-		"test": "svelte-kit sync && pnpm build && vitest run",
+		"test": "vitest run",
 		"test:cross-platform": "pnpm test"
 	},
 	"devDependencies": {

packages/kit/test/prerendering/basics/src/routes/missing-id/+page.svelte

@@ -0,0 +1,2 @@
+<a href="#missing-id">Bad link</a>
+<a href="#top">Bad link</a>

packages/kit/test/prerendering/basics/svelte.config.js

@@ -1,4 +1,5 @@
 import adapter from '../../../../adapter-static/index.js';
+import { writeFileSync } from 'node:fs';
 
 /** @type {import('@sveltejs/kit').Config} */
 const config = {
@@ -7,7 +8,10 @@ const config = {
 
 		prerender: {
 			handleHttpError: 'warn',
-			origin: 'http://prerender.origin'
+			origin: 'http://prerender.origin',
+			handleMissingId: ({ id }) => {
+				writeFileSync('./missing_ids/index.jsonl', JSON.stringify(id) + ',', 'utf-8');
+			}
 		}
 	}
 };

packages/kit/test/prerendering/basics/test/tests.spec.js

@@ -258,3 +258,10 @@ test('crawls links that start with config.prerender.origin', () => {
 	const content = read('prerender-origin/dynamic.html');
 	expect(content).toBeTruthy();
 });
+
+test('identifies missing ids', () => {
+	const missing_ids_file = fileURLToPath(new URL('../missing_ids/index.jsonl', import.meta.url));
+	const missing_ids_content = fs.readFileSync(missing_ids_file, 'utf-8');
+	const missing_ids = JSON.parse(`[${missing_ids_content.slice(0, -1)}]`);
+	expect(missing_ids).toEqual(['missing-id']);
+});

packages/kit/test/prerendering/basics/vite.config.js

@@ -1,7 +1,7 @@
 import * as path from 'node:path';
 import { sveltekit } from '@sveltejs/kit/vite';
 
-/** @type {import('vite').UserConfig} */
+/** @type {import('vitest/config').UserConfig} */
 const config = {
 	build: {
 		minify: false
@@ -21,6 +21,10 @@ const config = {
 		fs: {
 			allow: [path.resolve('../../../src')]
 		}
+	},
+
+	test: {
+		globalSetup: './globalSetup.js'
 	}
 };