[fix] route invalidation comparison based on url and route, not on id (#8399)

Fixes #8398

Author: Algoinde

.changeset/sweet-hairs-roll.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+fix route id comparison for load change detection

packages/kit/src/runtime/client/client.js

@@ -709,7 +709,7 @@ export function create_client({ target, base }) {
 		let server_data = null;
 
 		const url_changed = current.url ? id !== current.url.pathname + current.url.search : false;
-		const route_changed = current.route ? id !== current.route.id : false;
+		const route_changed = current.route ? route.id !== current.route.id : false;
 
 		const invalid_server_nodes = loaders.reduce((acc, loader, i) => {
 			const previous = current.branch[i];

packages/kit/test/apps/basics/src/routes/load/invalidation/route/shared/+layout.js

@@ -1,4 +1,4 @@
 /** @type {import('./$types').LayoutLoad} */
 export function load({ route }) {
-	return { route };
+	return { route, random: Math.random() };
 }

packages/kit/test/apps/basics/src/routes/load/invalidation/route/shared/+layout.svelte

@@ -4,7 +4,11 @@
 </script>
 
 <h1>route.id: {data.route.id}</h1>
+<h2>random id: {data.random}</h2>
 <slot />
 
 <a href="/load/invalidation/route/shared/a">/load/invalidation/route/shared/a</a>
 <a href="/load/invalidation/route/shared/b">/load/invalidation/route/shared/b</a>
+
+<a href="/load/invalidation/route/shared/unchanged-x">/load/invalidation/route/shared/unchanged-x</a>
+<a href="/load/invalidation/route/shared/unchanged-y">/load/invalidation/route/shared/unchanged-y</a>

packages/kit/test/apps/basics/src/routes/load/invalidation/route/shared/[x]/+page.svelte

@@ -0,0 +1 @@
+<p>[x]</p>

packages/kit/test/apps/basics/test/client.test.js

@@ -1069,6 +1069,16 @@ test.describe('Invalidation', () => {
 		expect(await page.textContent('h1')).toBe('route.id: /load/invalidation/route/shared/b');
 	});
 
+	test('route.id does not rerun layout if unchanged', async ({ page, clicknav }) => {
+		await page.goto('/load/invalidation/route/shared/unchanged-x');
+		expect(await page.textContent('h1')).toBe('route.id: /load/invalidation/route/shared/[x]');
+		const id = await page.textContent('h2');
+
+		await clicknav('[href="/load/invalidation/route/shared/unchanged-y"]');
+		expect(await page.textContent('h1')).toBe('route.id: /load/invalidation/route/shared/[x]');
+		expect(await page.textContent('h2')).toBe(id);
+	});
+
 	test('$page.url can safely be mutated', async ({ page }) => {
 		await page.goto('/load/mutated-url?q=initial');
 		await expect(page.getByText('initial')).toBeVisible();