breaking: make page.url immutable on a type level

.changeset/easy-pianos-float.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': major
+---
+
+breaking: make `page.url` immutable on a type level

packages/kit/src/exports/public.d.ts

@@ -1454,7 +1454,7 @@ export interface Page<
 	/**
 	 * The URL of the current page.
 	 */
-	url: URL & { pathname: ResolvedPathname };
+	url: ReadonlyURL & { readonly pathname: ResolvedPathname | (string & {}) };
 	/**
 	 * The parameters of the current page - e.g. for a route like `/blog/[slug]`, a `{ slug: string }` object.
 	 */
@@ -1995,6 +1995,14 @@ export interface Snapshot<T = any> {
 	restore: (snapshot: T) => void;
 }
 
+export type ReadonlyURLSearchParams = Omit<URLSearchParams, 'set' | 'append' | 'delete' | 'sort'>;
+
+export type ReadonlyURL = Readonly<
+	Omit<URL, 'searchParams'> & {
+		searchParams: ReadonlyURLSearchParams;
+	}
+>;
+
 // If T is unknown or has an index signature, the types below will recurse indefinitely and create giant unions that TS can't handle
 type WillRecurseIndefinitely<T> = unknown extends T ? true : string extends keyof T ? true : false;
 

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

@@ -2649,7 +2649,7 @@ export async function applyAction(result) {
 		root.$set({ form: result.data });
 
 		if (result.type === 'success') {
-			reset_focus(page.url);
+			reset_focus(/** @type {URL} */ (page.url));
 		}
 	}
 }

packages/kit/test/apps/basics/src/routes/load/mutated-url/+page.svelte

@@ -6,7 +6,9 @@
 	let { data } = $props();
 
 	function update_q() {
+		// @ts-expect-error set is not in the types; we wanna test here that we guard against mutation in goto, too
 		page.url.searchParams.set('q', 'updated');
+		// @ts-expect-error
 		goto(page.url);
 	}
 </script>

packages/kit/test/apps/basics/src/routes/query/echo/utils.js

@@ -1,6 +1,6 @@
 /** @typedef {Record<string, string[]>} Query */
 
-/** @param {URLSearchParams} query */
+/** @param {import("@sveltejs/kit").ReadonlyURLSearchParams} query */
 export function to_pojo(query) {
 	/** @type {Query}*/
 	const values = {};

packages/kit/test/apps/basics/src/routes/state/url/+page.svelte

@@ -8,7 +8,9 @@
 <button
 	type="button"
 	onclick={() => {
+		// @ts-expect-error set is not in the types; we wanna test here that we guard against mutation in goto, too
 		page.url.searchParams.set('q', 'test');
+		// @ts-expect-error
 		goto(page.url);
 	}}>test</button
 >

packages/kit/test/apps/basics/src/routes/xss/query/utils.js

@@ -1,6 +1,6 @@
 /** @typedef {Record<string, string[]>} Query */
 
-/** @param {URLSearchParams} query */
+/** @param {import("@sveltejs/kit").ReadonlyURLSearchParams} query */
 export function to_pojo(query) {
 	/** @type {Query}*/
 	const values = {};

packages/kit/types/index.d.ts

@@ -1427,7 +1427,7 @@ declare module '@sveltejs/kit' {
 		/**
 		 * The URL of the current page.
 		 */
-		url: URL & { pathname: ResolvedPathname };
+		url: ReadonlyURL & { readonly pathname: ResolvedPathname | (string & {}) };
 		/**
 		 * The parameters of the current page - e.g. for a route like `/blog/[slug]`, a `{ slug: string }` object.
 		 */
@@ -1966,6 +1966,14 @@ declare module '@sveltejs/kit' {
 		restore: (snapshot: T) => void;
 	}
 
+	export type ReadonlyURLSearchParams = Omit<URLSearchParams, 'set' | 'append' | 'delete' | 'sort'>;
+
+	export type ReadonlyURL = Readonly<
+		Omit<URL, 'searchParams'> & {
+			searchParams: ReadonlyURLSearchParams;
+		}
+	>;
+
 	// If T is unknown or has an index signature, the types below will recurse indefinitely and create giant unions that TS can't handle
 	type WillRecurseIndefinitely<T> = unknown extends T ? true : string extends keyof T ? true : false;