throw load validation errors so they are caught by handleError (#4953)

* throw load validation errors so they are caught by handleError - closes #3388

* remove .only

* always remove errors.json to make local testing more consistent with CI

* format

* fix test

* force cache to clear

* gah

* Update packages/kit/src/cli.js

.changeset/famous-birds-cheer.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+Throw load validation errors so that they are caught by handleError

packages/kit/src/runtime/load.js

@@ -46,19 +46,13 @@ export function normalize(loaded) {
 
 	if (loaded.redirect) {
 		if (!loaded.status || Math.floor(loaded.status / 100) !== 3) {
-			return {
-				status: 500,
-				error: new Error(
-					'"redirect" property returned from load() must be accompanied by a 3xx status code'
-				)
-			};
+			throw new Error(
+				'"redirect" property returned from load() must be accompanied by a 3xx status code'
+			);
 		}
 
 		if (typeof loaded.redirect !== 'string') {
-			return {
-				status: 500,
-				error: new Error('"redirect" property returned from load() must be a string')
-			};
+			throw new Error('"redirect" property returned from load() must be a string');
 		}
 	}
 
@@ -67,10 +61,7 @@ export function normalize(loaded) {
 			!Array.isArray(loaded.dependencies) ||
 			loaded.dependencies.some((dep) => typeof dep !== 'string')
 		) {
-			return {
-				status: 500,
-				error: new Error('"dependencies" property returned from load() must be of type string[]')
-			};
+			throw new Error('"dependencies" property returned from load() must be of type string[]');
 		}
 	}
 

packages/kit/test/apps/basics/package.json

@@ -8,8 +8,8 @@
 		"preview": "node ../../cli.js preview",
 		"check": "tsc && svelte-check",
 		"test": "npm run test:dev && npm run test:build",
-		"test:dev": "cross-env DEV=true playwright test",
-		"test:build": "playwright test"
+		"test:dev": "rimraf test/errors.json && cross-env DEV=true playwright test",
+		"test:build": "rimraf test/errors.json && playwright test"
 	},
 	"devDependencies": {
 		"@sveltejs/kit": "workspace:*",

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

@@ -1927,7 +1927,13 @@ test.describe.parallel('Redirects', () => {
 		}
 	});
 
-	test('errors on missing status', async ({ baseURL, page, clicknav }) => {
+	test('errors on missing status', async ({
+		baseURL,
+		page,
+		clicknav,
+		javaScriptEnabled,
+		read_errors
+	}) => {
 		await page.goto('/redirect');
 
 		await clicknav('[href="/redirect/missing-status/a"]');
@@ -1937,6 +1943,14 @@ test.describe.parallel('Redirects', () => {
 		expect(await page.textContent('#message')).toBe(
 			'This is your custom error page saying: ""redirect" property returned from load() must be accompanied by a 3xx status code"'
 		);
+
+		if (!javaScriptEnabled) {
+			// handleError is not invoked for client-side navigation
+			const lines = read_errors('/redirect/missing-status/a').split('\n');
+			expect(lines[0]).toBe(
+				'Error: "redirect" property returned from load() must be accompanied by a 3xx status code'
+			);
+		}
 	});
 
 	test('errors on invalid status', async ({ baseURL, page, clicknav }) => {