fix: only preload link if the URL differs from current page (#12773)

fixes #10234

By avoiding preloading pages where the URL pathname and search params (the load ID) are unchanged, we also avoid mistakenly caching navigation results for hash URLs. Currently, these are ID'd the same as URLs without hashes, causing navigation to lose track of the current URL (hence the original issue).

This should be a good solution because:

- if we're on already on the page we don't need new load results for it.
- even if the load results are suppose to be different for the same URL, clicking on a link that leads to the exact same URL already does nothing.

.changeset/calm-fireants-hug.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+fix: only preload links that have a different URL than the current page

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

@@ -1543,7 +1543,10 @@ function setup_preload() {
 
 		const options = get_router_options(a);
 
-		if (!options.reload) {
+		// we don't want to preload data for a page we're already on
+		const same_url = url && current.url.pathname + current.url.search === url.pathname + url.search;
+
+		if (!options.reload && !same_url) {
 			if (priority <= options.preload_data) {
 				const intent = get_navigation_intent(url, false);
 				if (intent) {

packages/kit/test/apps/basics/src/routes/routing/hashes/a/+page.svelte

@@ -2,3 +2,6 @@
 <a href="#hash-target">hash link</a>
 <a href="/routing/hashes/b">b</a>
 <a href="#replace-state" data-sveltekit-replacestate>replace state</a>
+
+<a data-sveltekit-preload-data href="/routing/hashes/a">/routing/hashes/a</a>
+<a data-sveltekit-preload-data href="#preload">#preload</a>

packages/kit/test/apps/basics/test/cross-platform/client.test.js

@@ -615,6 +615,19 @@ test.describe('Prefetching', () => {
 		await expect(page.locator('h1')).not.toHaveText('Oopsie');
 	});
 
+	test('same route hash links work more than once', async ({ page, clicknav, baseURL }) => {
+		await page.goto('/routing/hashes/a');
+
+		await clicknav('[href="#preload"]');
+		await expect(page.url()).toBe(`${baseURL}/routing/hashes/a#preload`);
+
+		await clicknav('[href="/routing/hashes/a"]');
+		await expect(page.url()).toBe(`${baseURL}/routing/hashes/a`);
+
+		await clicknav('[href="#preload"]');
+		await expect(page.url()).toBe(`${baseURL}/routing/hashes/a#preload`);
+	});
+
 	test('does not rerun load on calls to duplicate preload hash route', async ({ app, page }) => {
 		await page.goto('/routing/a');