make 404 more helpful if paths.base is missing - closes #5465

.changeset/clean-schools-doubt.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+Make 404 error more helpful if paths.base is missing

packages/kit/src/core/prerender/prerender.js

@@ -14,25 +14,17 @@ import { escape_html_attr } from '../../utils/escape.js';
  * @typedef {import('types').Logger} Logger
  */
 
-/** @type {(details: Parameters<PrerenderErrorHandler>[0] ) => string} */
-function format_error({ status, path, referrer, referenceType }) {
- return `${status} ${path}${referrer ? ` (${referenceType} from ${referrer})` : ''}`;
-}
+/**
+ * @param {Parameters<PrerenderErrorHandler>[0]} details
+ * @param {import('types').ValidatedKitConfig} config
+ */
+function format_error({ status, path, referrer, referenceType }, config) {
+ const message =
+ status === 404 && !path.startsWith(config.paths.base)
+ ? `${path} does not begin with \`paths.base\``
+ : path;
 
-/** @type {(log: Logger, onError: OnError) => PrerenderErrorHandler} */
-function normalise_error_handler(log, onError) {
- switch (onError) {
- case 'continue':
- return (details) => {
- log.error(format_error(details));
- };
- case 'fail':
- return (details) => {
- throw new Error(format_error(details));
- };
- default:
- return onError;
- }
+ return `${status} ${message}${referrer ? ` (${referenceType} from ${referrer})` : ''}`;
 }
 
 const OK = 2;
@@ -75,7 +67,20 @@ export async function prerender({ config, entries, files, log }) {
 
  const server = new Server(manifest);
 
- const error = normalise_error_handler(log, config.prerender.onError);
+ /** @type {PrerenderErrorHandler} */
+ let error;
+
+ if (config.prerender.onError === 'continue') {
+ error = (details) => {
+ log.error(format_error(details, config));
+ };
+ } else if (config.prerender.onError === 'fail') {
+ error = (details) => {
+ throw new Error(format_error(details, config));
+ };
+ } else {
+ error = config.prerender.onError;
+ }
 
  const q = queue(config.prerender.concurrency);