Nested error components

.changeset/rude-tomatoes-thank.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+Allow non-root \$error.svelte components

documentation/docs/02-layouts.md

@@ -62,17 +62,32 @@ We can create a layout that only applies to pages below `/settings` (while inher
 <slot></slot>
 ```
 
-
 ### Error pages
 
-If your page fails to load (see [Loading](#loading)), SvelteKit will render an error page. You can customise this page by creating a file called `src/routes/$error.svelte`, which is a component that receives an `error` prop alongside a `status` code:
+If a page fails to load (see [Loading](#loading)), SvelteKit will render an error page. You can customise this page by creating `$error.svelte` components alongside your layout and page components.
+
+For example, if `src/routes/settings/notifications/index.svelte` failed to load, SvelteKit would render `src/routes/settings/notifications/$error.svelte` in the same layout, if it existed. If not, it would render `src/routes/settings/$error.svelte` in the parent layout, or `src/routes/$error.svelte` in the root layout.
+
+> SvelteKit provides a default error page in case you don't supply `src/routes/$error.svelte`, but it's recommend that you bring your own.
+
+If an error component has a [`load`](#loading) function, it will be called with `error` and `status` properties:
 
 ```html
+<script context="module">
+	export function load({ error, status }) {
+		return {
+			props: {
+				title: `${status}: ${error.message}`
+			}
+		};
+	}
+</script>
+
 <script>
-	export let status;
-	export let error;
+	export let title;
 </script>
 
-<h1>{status}</h1>
-<p>{error.message}</p>
-```
+<h1>{title}</h1>
+```
+
+> Server-side stack traces will be removed from `error` in production, to avoid exposing privileged information to users.

packages/kit/src/core/build/index.js

@@ -281,7 +281,8 @@ async function build_server(
 									type: 'page',
 									pattern: ${route.pattern},
 									params: ${params},
-									parts: [${route.parts.map(file => s(file)).join(', ')}]
+									a: [${route.a.map(file => file && s(file)).join(', ')}],
+									b: [${route.b.map(file => file && s(file)).join(', ')}]
 								}`;
 					} else {
 						const params = get_params(route.params);

packages/kit/src/core/create_app/index.js

@@ -65,6 +65,10 @@ function generate_client_manifest(manifest_data, base) {
 			.join(',\n\t\t\t\t')}
 	]`.replace(/^\t/gm, '');
 
+	/** @param {string[]} parts */
+	const get_indices = (parts) =>
+		`[${parts.map((part) => (part ? `c[${component_indexes[part]}]` : '')).join(', ')}]`;
+
 	const routes = `[
 		${manifest_data.routes
 			.map((route) => {
@@ -81,15 +85,10 @@ function generate_client_manifest(manifest_data, base) {
 								.join(', ') +
 							'})';
 
-					const tuple = [
-						route.pattern,
-						`[${route.parts.map((part) => `components[${component_indexes[part]}]`).join(', ')}]`,
-						params
-					]
-						.filter(Boolean)
-						.join(', ');
+					const tuple = [route.pattern, get_indices(route.a), get_indices(route.b)];
+					if (params) tuple.push(params);
 
-					return `// ${route.parts[route.parts.length - 1]}\n\t\t[${tuple}]`;
+					return `// ${route.a[route.a.length - 1]}\n\t\t[${tuple.join(', ')}]`;
 				} else {
 					return `// ${route.file}\n\t\t[${route.pattern}]`;
 				}
@@ -98,13 +97,13 @@ function generate_client_manifest(manifest_data, base) {
 	]`.replace(/^\t/gm, '');
 
 	return trim(`
-		const components = ${components};
+		const c = ${components};
 
 		const d = decodeURIComponent;
 
 		export const routes = ${routes};
 
-		export const fallback = [components[0](), components[1]()];
+		export const fallback = [c[0](), c[1]()];
 	`);
 }
 
@@ -117,7 +116,7 @@ function generate_app(manifest_data, base) {
 
 	const max_depth = Math.max(
 		...manifest_data.routes.map((route) =>
-			route.type === 'page' ? route.parts.filter(Boolean).length : 0
+			route.type === 'page' ? route.a.filter(Boolean).length : 0
 		)
 	);
 
@@ -132,9 +131,7 @@ function generate_app(manifest_data, base) {
 
 	while (l--) {
 		pyramid = `
-			<svelte:component this={components[${l}]} {...(props_${l} || {})}${
-			l === 1 ? ' {status} {error}' : '' // TODO this is awkward
-		}>
+			<svelte:component this={components[${l}]} {...(props_${l} || {})}>
 				{#if components[${l + 1}]}
 					${pyramid.replace(/\n/g, '\n\t\t\t\t\t')}
 				{/if}
@@ -149,10 +146,6 @@ function generate_app(manifest_data, base) {
 		<script>
 			import { setContext, afterUpdate, onMount } from 'svelte';
 
-			// error handling
-			export let status = undefined;
-			export let error = undefined;
-
 			// stores
 			export let stores;
 			export let page;

packages/kit/src/core/create_manifest_data/index.js

@@ -50,9 +50,10 @@ export default function create_manifest_data({ config, output, cwd = process.cwd
 	 * @param {string} dir
 	 * @param {Part[][]} parent_segments
 	 * @param {string[]} parent_params
-	 * @param {string[]} stack
+	 * @param {string[]} layout_stack // accumulated $layout.svelte components
+	 * @param {string[]} error_stack // accumulated $error.svelte components
 	 */
-	function walk(dir, parent_segments, parent_params, stack) {
+	function walk(dir, parent_segments, parent_params, layout_stack, error_stack) {
 		/** @type {Item[]} */
 		const items = fs
 			.readdirSync(dir)
@@ -138,31 +139,48 @@ export default function create_manifest_data({ config, output, cwd = process.cwd
 			params.push(...item.parts.filter((p) => p.dynamic).map((p) => p.content));
 
 			if (item.is_dir) {
-				const component = find_layout('$layout', item.file);
+				const layout = find_layout('$layout', item.file);
+				const error = find_layout('$error', item.file);
 
-				if (component) components.push(component);
+				if (layout) components.push(layout);
+				if (error) components.push(error);
 
 				walk(
 					path.join(dir, item.basename),
 					segments,
 					params,
-					component ? stack.concat(component) : stack
+					layout_stack.concat(layout),
+					error_stack.concat(error)
 				);
 			} else if (item.is_page) {
 				components.push(item.file);
 
-				const parts =
-					item.is_index && stack[stack.length - 1] === null
-						? stack.slice(0, -1).concat(item.file)
-						: stack.concat(item.file);
+				const a = layout_stack.concat(item.file);
+				const b = error_stack;
 
 				const pattern = get_pattern(segments, true);
 
+				let i = a.length;
+				while (i--) {
+					if (!b[i] && !a[i]) {
+						b.splice(i, 1);
+						a.splice(i, 1);
+					}
+				}
+
+				i = b.length;
+				while (i--) {
+					if (b[i]) break;
+				}
+
+				b.splice(i + 1);
+
 				routes.push({
 					type: 'page',
 					pattern,
 					params,
-					parts
+					a,
+					b
 				});
 			} else {
 				const pattern = get_pattern(segments, !item.route_suffix);
@@ -184,7 +202,7 @@ export default function create_manifest_data({ config, output, cwd = process.cwd
 
 	components.push(layout, error);
 
-	walk(config.kit.files.routes, [], [], [layout]);
+	walk(config.kit.files.routes, [], [], [layout], [error]);
 
 	const assets_dir = config.kit.files.assets;
 

packages/kit/src/core/create_manifest_data/index.spec.js

@@ -47,14 +47,16 @@ test('creates routes', () => {
 			type: 'page',
 			pattern: /^\/$/,
 			params: [],
-			parts: [layout, index]
+			a: [layout, index],
+			b: [error]
 		},
 
 		{
 			type: 'page',
 			pattern: /^\/about\/?$/,
 			params: [],
-			parts: [layout, about]
+			a: [layout, about],
+			b: [error]
 		},
 
 		{
@@ -68,7 +70,8 @@ test('creates routes', () => {
 			type: 'page',
 			pattern: /^\/blog\/?$/,
 			params: [],
-			parts: [layout, blog]
+			a: [layout, blog],
+			b: [error]
 		},
 
 		{
@@ -82,7 +85,8 @@ test('creates routes', () => {
 			type: 'page',
 			pattern: /^\/blog\/([^/]+?)\/?$/,
 			params: ['slug'],
-			parts: [layout, blog_$slug]
+			a: [layout, blog_$slug],
+			b: [error]
 		}
 	]);
 });
@@ -103,14 +107,16 @@ test('creates routes with layout', () => {
 			type: 'page',
 			pattern: /^\/$/,
 			params: [],
-			parts: [layout, index]
+			a: [layout, index],
+			b: [error]
 		},
 
 		{
 			type: 'page',
 			pattern: /^\/foo\/?$/,
 			params: [],
-			parts: [layout, foo_$layout, foo]
+			a: [layout, foo_$layout, foo],
+			b: [error]
 		}
 	]);
 });
@@ -146,7 +152,7 @@ test('sorts routes correctly', () => {
 	const { routes } = create('samples/sorting');
 
 	assert.equal(
-		routes.map((p) => (p.type === 'page' ? p.parts : p.file)),
+		routes.map((p) => (p.type === 'page' ? p.a : p.file)),
 		[
 			[layout, 'samples/sorting/index.svelte'],
 			[layout, 'samples/sorting/about.svelte'],
@@ -254,14 +260,16 @@ test('works with custom extensions', () => {
 			type: 'page',
 			pattern: /^\/$/,
 			params: [],
-			parts: [layout, index]
+			a: [layout, index],
+			b: [error]
 		},
 
 		{
 			type: 'page',
 			pattern: /^\/about\/?$/,
 			params: [],
-			parts: [layout, about]
+			a: [layout, about],
+			b: [error]
 		},
 
 		{
@@ -275,7 +283,8 @@ test('works with custom extensions', () => {
 			type: 'page',
 			pattern: /^\/blog\/?$/,
 			params: [],
-			parts: [layout, blog]
+			a: [layout, blog],
+			b: [error]
 		},
 
 		{
@@ -289,7 +298,8 @@ test('works with custom extensions', () => {
 			type: 'page',
 			pattern: /^\/blog\/([^/]+?)\/?$/,
 			params: ['slug'],
-			parts: [layout, blog_$slug]
+			a: [layout, blog_$slug],
+			b: [error]
 		}
 	]);
 });
@@ -311,4 +321,29 @@ test('lists static assets', () => {
 	]);
 });
 
+test('includes nested error components', () => {
+	const { routes } = create('samples/nested-errors');
+
+	assert.equal(routes, [
+		{
+			type: 'page',
+			pattern: /^\/foo\/bar\/baz\/?$/,
+			params: [],
+			a: [
+				layout,
+				'samples/nested-errors/foo/$layout.svelte',
+				undefined,
+				'samples/nested-errors/foo/bar/baz/$layout.svelte',
+				'samples/nested-errors/foo/bar/baz/index.svelte'
+			],
+			b: [
+				error,
+				undefined,
+				'samples/nested-errors/foo/bar/$error.svelte',
+				'samples/nested-errors/foo/bar/baz/$error.svelte'
+			]
+		}
+	]);
+});
+
 test.run();

packages/kit/src/core/dev/index.js

@@ -263,14 +263,12 @@ class Watcher extends EventEmitter {
 								handle: hooks.handle || ((request, render) => render(request))
 							},
 							only_render_prerenderable_pages: false,
-							// get_component_path: (id) => `/${id}?import`,
 							get_stack: (error) => {
 								this.vite.ssrFixStacktrace(error);
 								return error.stack;
 							},
 							get_static_file: (file) =>
 								fs.readFileSync(path.join(this.config.kit.files.assets, file)),
-							// get_amp_css: (url) => '', // TODO: implement this
 							ssr: this.config.kit.ssr,
 							router: this.config.kit.router,
 							hydrate: this.config.kit.hydrate
@@ -316,7 +314,8 @@ class Watcher extends EventEmitter {
 						type: 'page',
 						pattern: route.pattern,
 						params: get_params(route.params),
-						parts: route.parts
+						a: route.a,
+						b: route.b
 					};
 				}