TypeError: Cannot read properties of undefined (reading 'replace') at escape_html

[rChaoz]

Describe the bug

Instead of an error page, I'm getting a blank page (no HTML even, just text) with the content:

TypeError: Cannot read properties of undefined (reading 'replace') at escape_html (eval at runInlinedModule (file:///C:/Users/.../node_modules/vite/dist/node/module-runner.js:1062:11), :55:26) at static_error_page (eval at runInlinedModule (file:///C:/Users/.../node_modules/vite/dist/node/module-runner.js:1062:11), :46:94) at handle_fatal_error (eval at runInlinedModule (file:///C:/Users/.../node_modules/vite/dist/node/module-runner.js:1062:11), :68:10) at async respond (eval at runInlinedModule (file:///C:/Users/.../node_modules/vite/dist/node/module-runner.js:1062:11), :336:12) at async file:///C:/Users/.../node_modules/@sveltejs/kit/src/exports/vite/dev/index.js:540:22

I've looked a bit into the functions from the stacktrace and it seems like this function is the problem:

kit/packages/kit/src/runtime/server/utils.js

Lines 99 to 116 in 217fc24

	export async function handle_error_and_jsonify(event, options, error) {
	if (error instanceof HttpError) {
	return error.body;
	}
	if (__SVELTEKIT_DEV__ && typeof error == 'object') {
	fix_stack_trace(error);
	}
	const status = get_status(error);
	const message = get_message(error);
	return (
	(await with_event(event, () =>
	options.hooks.handleError({ error, event, status, message })
	)) ?? { message }
	);
	}

It promises to return an object that always has a string message property, but in case of an HttpError (first if statement in the function), this is not true. The error is defined by App.Error, which is user-arbitrary.

Reproduction

Throw error(400, { code: 123 }) in the handle hook. This is allowed by TypeScript if using custom error using something like this in app.d.ts:

declare namespace App {
    // ...

    interface Error {
        code: number
        message?: string
    }
}

Severity

annoyance