[fix] handle hash links with non-ASCII characters when prerendering (#7729)

fixes #7728

Author: Rich-Harris

.changeset/new-kangaroos-double.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+Handle hash links with non-ASCII characters when prerendering

packages/kit/src/core/prerender/fixtures/ids/input.html

@@ -1,3 +1,6 @@
 <h2 id="before">before</h2>
 <span data-x='"\\"'>backslash</span>
-<h2 id="after">after</h2>
+<h2 id="after">after</h2>
+<h2 id="encöded">
+	<a href="#encöded">encöded</a>
+</h2>

packages/kit/src/core/prerender/fixtures/ids/output.json

@@ -1,4 +1,4 @@
 {
-	"hrefs": [],
-	"ids": ["before", "after"]
+	"hrefs": ["#encöded"],
+	"ids": ["before", "after", "encöded"]
 }

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

@@ -137,7 +137,7 @@ export async function prerender() {
 		config.prerender.handleMissingId,
 		({ path, id, referrers }) => {
 			return (
-				`The following pages contain links to ${path}#${id}, but no element with id="${id}" exists on ${path}:` +
+				`The following pages contain links to ${path}#${id}, but no element with id="${id}" exists on ${path} - see the \`handleMissingId\` option in https://kit.svelte.dev/docs/configuration#prerender for more info:` +
 				referrers.map((l) => `\n  - ${l}`).join('')
 			);
 		}
@@ -262,11 +262,13 @@ export async function prerender() {
 				}
 
 				if (hash) {
-					if (!expected_hashlinks.has(pathname + hash)) {
-						expected_hashlinks.set(pathname + hash, new Set());
+					const key = decodeURI(pathname + hash);
+
+					if (!expected_hashlinks.has(key)) {
+						expected_hashlinks.set(key, new Set());
 					}
 
-					/** @type {Set<string>} */ (expected_hashlinks.get(pathname + hash)).add(decoded);
+					/** @type {Set<string>} */ (expected_hashlinks.get(key)).add(decoded);
 				}
 
 				enqueue(decoded, decodeURI(pathname), pathname);

packages/kit/test/prerendering/basics/src/routes/encöded-hash-link/+page.svelte

@@ -0,0 +1,3 @@
+<h2 id="encöded">
+	<a href="#encöded">encöded</a>
+</h2>