[fix] don't cache prefetch errors (#7610)

Fixes #6709

.changeset/serious-buttons-push.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+[fix] don't cache prefetch errors

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

@@ -218,7 +218,16 @@ export function create_client({ target, base, trailing_slash }) {
 			throw new Error(`Attempted to prefetch a URL that does not belong to this app: ${url}`);
 		}
 
-		load_cache = { id: intent.id, promise: load_route(intent) };
+		load_cache = {
+			id: intent.id,
+			promise: load_route(intent).then((result) => {
+				if (result.type === 'loaded' && result.state.error) {
+					// Don't cache errors, because they might be transient
+					load_cache = null;
+				}
+				return result;
+			})
+		};
 
 		return load_cache.promise;
 	}

packages/kit/test/apps/basics/src/routes/routing/prefetching/prefetch-error/+page.js

@@ -0,0 +1,9 @@
+let throw_error = false;
+
+/** @type {import('@sveltejs/kit').Load} */
+export async function load() {
+	throw_error = !throw_error;
+	if (throw_error) {
+		throw new Error('error');
+	}
+}

packages/kit/test/apps/basics/src/routes/routing/prefetching/prefetch-error/+page.svelte

@@ -0,0 +1 @@
+<p>hello</p>

packages/kit/test/apps/basics/src/routes/routing/prefetching/prefetched/+page.js

@@ -1,5 +1,5 @@
 /** @type {import('@sveltejs/kit').Load} */
 export async function load({ fetch }) {
-	const message = await fetch('/routing/prefetched.json').then((r) => r.json());
+	const message = await fetch('/routing/prefetching/prefetched.json').then((r) => r.json());
 	return { message };
 }

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

@@ -666,8 +666,8 @@ test.describe('Prefetching', () => {
 		// also wait for network processing to complete, see
 		// https://playwright.dev/docs/network#network-events
 		await Promise.all([
-			page.waitForResponse(`${baseURL}/routing/prefetched.json`),
-			app.prefetch('/routing/prefetched')
+			page.waitForResponse(`${baseURL}/routing/prefetching/prefetched.json`),
+			app.prefetch('/routing/prefetching/prefetched')
 		]);
 
 		// svelte request made is environment dependent
@@ -679,10 +679,10 @@ test.describe('Prefetching', () => {
 			expect(requests.filter((req) => req.endsWith('.js')).length).toBeGreaterThan(0);
 		}
 
-		expect(requests.includes(`${baseURL}/routing/prefetched.json`)).toBe(true);
+		expect(requests.includes(`${baseURL}/routing/prefetching/prefetched.json`)).toBe(true);
 
 		requests = [];
-		await app.goto('/routing/prefetched');
+		await app.goto('/routing/prefetching/prefetched');
 		expect(requests).toEqual([]);
 
 		try {
@@ -698,28 +698,36 @@ test.describe('Prefetching', () => {
 		page
 	}) => {
 		await page.goto('/routing/a');
-		await app.prefetch('/routing/prefetched/hash-route#please-dont-show-me');
-		await app.goto('/routing/prefetched/hash-route');
+		await app.prefetch('/routing/prefetching/hash-route#please-dont-show-me');
+		await app.goto('/routing/prefetching/hash-route');
 		await expect(page.locator('h1')).not.toHaveText('Oopsie');
 	});
 
 	test('does not rerun load on calls to duplicate preload hash route', async ({ app, page }) => {
 		await page.goto('/routing/a');
 
-		await app.prefetch('/routing/prefetched/hash-route#please-dont-show-me');
-		await app.prefetch('/routing/prefetched/hash-route#please-dont-show-me');
-		await app.goto('/routing/prefetched/hash-route#please-dont-show-me');
+		await app.prefetch('/routing/prefetching/hash-route#please-dont-show-me');
+		await app.prefetch('/routing/prefetching/hash-route#please-dont-show-me');
+		await app.goto('/routing/prefetching/hash-route#please-dont-show-me');
 		await expect(page.locator('p')).toHaveText('Loaded 1 times.');
 	});
 
 	test('does not rerun load on calls to different preload hash route', async ({ app, page }) => {
 		await page.goto('/routing/a');
 
-		await app.prefetch('/routing/prefetched/hash-route#please-dont-show-me');
-		await app.prefetch('/routing/prefetched/hash-route#please-dont-show-me-jr');
-		await app.goto('/routing/prefetched/hash-route#please-dont-show-me');
+		await app.prefetch('/routing/prefetching/hash-route#please-dont-show-me');
+		await app.prefetch('/routing/prefetching/hash-route#please-dont-show-me-jr');
+		await app.goto('/routing/prefetching/hash-route#please-dont-show-me');
 		await expect(page.locator('p')).toHaveText('Loaded 1 times.');
 	});
+
+	test('does rerun load when prefetch errored', async ({ app, page }) => {
+		await page.goto('/routing/a');
+
+		await app.prefetch('/routing/prefetching/prefetch-error');
+		await app.goto('/routing/prefetching/prefetch-error');
+		await expect(page.locator('p')).toHaveText('hello');
+	});
 });
 
 test.describe('Routing', () => {