fix: discard a consumed preloaded redirect before following it

.changeset/pre/quiet-preload-redirect.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+fix: don't replay a preloaded redirect when a later hop of the navigation returns to the route

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

@@ -2072,6 +2072,9 @@ async function navigate({
 	if (navigation_result.type === 'redirect') {
 		// whatwg fetch spec https://fetch.spec.whatwg.org/#http-redirect-fetch says to error after 20 redirects
 		if (redirect_count < 20) {
+			// a preloaded redirect has been consumed; a later hop back to this route must load afresh
+			if (load_cache?.id === intent?.id) discard_load_cache();
+
 			await navigate({
 				type,
 				url: new URL(navigation_result.location, url),

packages/kit/test/apps/basics/src/routes/routing/preloading/redirect/[step]/+page.server.js

@@ -0,0 +1,13 @@
+import { redirect } from '@sveltejs/kit';
+
+/** @type {import('./$types').PageServerLoad} */
+export function load({ cookies, params }) {
+	if (params.step === 'resolve') {
+		cookies.set('preload-redirect-resolved', 'true', { path: '/routing/preloading/redirect' });
+		redirect(303, '/routing/preloading/redirect/target');
+	}
+
+	if (!cookies.get('preload-redirect-resolved')) {
+		redirect(303, '/routing/preloading/redirect/resolve');
+	}
+}

packages/kit/test/apps/basics/src/routes/routing/preloading/redirect/[step]/+page.svelte

@@ -0,0 +1 @@
+<h1>Redirect resolved</h1>

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

@@ -148,7 +148,7 @@
 });
 
 test.describe('Navigation lifecycle functions', () => {
 	test('beforeNavigate prevents navigation triggered by link click', async ({ page, baseURL }) => {
 		await page.goto('/navigation-lifecycle/before-navigate/prevent-navigation');
 
 		await page.click('[href="/navigation-lifecycle/before-navigate/a"]');
@@ -207,7 +207,7 @@
 		expect(await page.innerHTML('pre')).toBe('1 true leave');
 	});
 
 	test('beforeNavigate is not triggered on redirect', async ({ page, baseURL }) => {
 		await page.goto('/navigation-lifecycle/before-navigate/prevent-navigation');
 
 		await page.click('[href="/navigation-lifecycle/before-navigate/redirect"]');
@@ -390,7 +390,7 @@
 		expect(afterNav.type).toBe('link');
 	});
 
 	test('scroll state is provided on popstate navigation', async ({ page, clicknav, scroll_to }) => {
 		await page.goto('/navigation-lifecycle/scroll-state/a');
 		await scroll_to(0, 500);
 
@@ -697,7 +697,7 @@
 		}
 	});
 
 	test('Scroll position is correct after going back from a shallow route', async ({
 		page,
 		scroll_to
 	}) => {
@@ -807,7 +807,7 @@
 		);
 	});
 
 	test('Root 404 redirects somewhere due to root layout', async ({ page, baseURL, clicknav }) => {
 		await page.goto('/errors/error-html');
 		await clicknav('button:text-is("Redirect")');
 		expect(page.url()).toBe(baseURL + '/load');
@@ -909,7 +909,7 @@
 		expect(requests.filter((r) => r.includes('__route.js'))).toEqual([]);
 	});
 
 	test('preloadCode caches endpoint-only route ids', async ({ page, app }) => {
 		await page.goto('/routing/a');
 
 		// first call discovers that `/set-cookie` exists but has no `+page`
@@ -1023,6 +1023,24 @@
 		);
 	});
 
+	test('does not replay a preloaded redirect when a later hop returns to the route', async ({
+		page,
+		app
+	}) => {
+		await page.goto('/routing/a');
+
+		// the cookie is unset, so the preload resolves to a redirect to /resolve
+		const target = '/routing/preloading/redirect/target';
+		expect(await app.preloadData(target)).toMatchObject({
+			type: 'redirect',
+			location: '/routing/preloading/redirect/resolve'
+		});
+
+		// /resolve sets the cookie and redirects back to /target, which must now load afresh
+		await app.goto(target);
+		await expect(page.locator('h1')).toHaveText('Redirect resolved');
+	});
+
 	test('chooses correct route when hash route is preloaded but regular route is clicked', async ({
 		app,
 		page
@@ -1060,7 +1078,7 @@
 		await expect(page.locator('p')).toHaveText('Loaded 1 times.');
 	});
 
 	test('does rerun load when preload errored', async ({ app, page }) => {
 		await page.goto('/routing/a');
 
 		await app.preloadData('/routing/preloading/preload-error');
@@ -1357,14 +1375,14 @@
 });
 
 test.describe('cookies', () => {
 	test('etag forwards cookies', async ({ page }) => {
 		await page.goto('/cookies/forwarded-in-etag');
 		await expect(page.locator('p')).toHaveText('foo=bar');
 		await page.locator('button').click();
 		await expect(page.locator('p')).toHaveText('foo=bar');
 	});
 
 	test('etag forwards multiple cookies', async ({ page }) => {
 		await page.goto('/cookies/forwarded-in-etag-multiple');
 		await expect(page.locator('p')).toHaveText('one=1; three=3; two=2');
 		await page.locator('button').click();