fix: lift unsafe_state_mutation constrained for SvelteDate, SvelteURL…

… and SvelteURLSearchParams created inside the derived
sveltejs · paoloricciuti · Jun 24, 2025 · Jun 24, 2025 · Jun 24, 2025 · Jun 24, 2025
commit a78460781192b90768686cde2e03da2f04fe981a
diff --git a/.changeset/fair-bats-visit.md b/.changeset/fair-bats-visit.md
@@ -2,4 +2,4 @@
 'svelte': patch
 ---
 
-lift unsafe_state_mutation constrained for SvelteSet and SvelteMap created inside the derived
+lift unsafe_state_mutation constraints for SvelteSet, SvelteMap, SvelteDate, SvelteURL and SvelteURLSearchParams created inside the derived
diff --git a/packages/svelte/src/reactivity/date.js b/packages/svelte/src/reactivity/date.js
@@ -1,6 +1,6 @@
 /** @import { Source } from '#client' */
 import { derived } from '../internal/client/index.js';
-import { source, set } from '../internal/client/reactivity/sources.js';
+import { set, state } from '../internal/client/reactivity/sources.js';
 import { tag } from '../internal/client/dev/tracing.js';
 import { active_reaction, get, set_active_reaction } from '../internal/client/runtime.js';
 import { DEV } from 'esm-env';
@@ -40,7 +40,7 @@ var inited = false;
  * ```
  */
 export class SvelteDate extends Date {
-	#time = source(super.getTime());
+	#time = state(super.getTime());
 
 	/** @type {Map<keyof Date, Source<unknown>>} */
 	#deriveds = new Map();

diff --git a/packages/svelte/src/reactivity/url-search-params.js b/packages/svelte/src/reactivity/url-search-params.js
@@ -1,5 +1,5 @@
 import { DEV } from 'esm-env';
-import { source } from '../internal/client/reactivity/sources.js';
+import { state } from '../internal/client/reactivity/sources.js';
 import { tag } from '../internal/client/dev/tracing.js';
 import { get } from '../internal/client/runtime.js';
 import { get_current_url } from './url.js';
@@ -34,7 +34,7 @@ export const REPLACE = Symbol();
  * ```
  */
 export class SvelteURLSearchParams extends URLSearchParams {
-	#version = DEV ? tag(source(0), 'SvelteURLSearchParams version') : source(0);
+	#version = DEV ? tag(state(0), 'SvelteURLSearchParams version') : state(0);
 	#url = get_current_url();
 
 	#updating = false;

diff --git a/packages/svelte/src/reactivity/url.js b/packages/svelte/src/reactivity/url.js
@@ -1,5 +1,5 @@
 import { DEV } from 'esm-env';
-import { source, set } from '../internal/client/reactivity/sources.js';
+import { set, state } from '../internal/client/reactivity/sources.js';
 import { tag } from '../internal/client/dev/tracing.js';
 import { get } from '../internal/client/runtime.js';
 import { REPLACE, SvelteURLSearchParams } from './url-search-params.js';
@@ -40,14 +40,14 @@ export function get_current_url() {
  * ```
  */
 export class SvelteURL extends URL {
-	#protocol = source(super.protocol);
-	#username = source(super.username);
-	#password = source(super.password);
-	#hostname = source(super.hostname);
-	#port = source(super.port);
-	#pathname = source(super.pathname);
-	#hash = source(super.hash);
-	#search = source(super.search);
+	#protocol = state(super.protocol);
+	#username = state(super.username);
+	#password = state(super.password);
+	#hostname = state(super.hostname);
+	#port = state(super.port);
+	#pathname = state(super.pathname);
+	#hash = state(super.hash);
+	#search = state(super.search);
 	#searchParams;
 
 	/**

diff --git a/packages/svelte/tests/runtime-runes/samples/side-effect-derived-date/_config.js b/packages/svelte/tests/runtime-runes/samples/side-effect-derived-date/_config.js
@@ -0,0 +1,23 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	compileOptions: {
+		dev: true,
+		runes: true
+	},
+
+	test({ assert, target }) {
+		const [button1, button2] = target.querySelectorAll('button');
+
+		assert.throws(() => {
+			button1?.click();
+			flushSync();
+		}, /state_unsafe_mutation/);
+
+		assert.doesNotThrow(() => {
+			button2?.click();
+			flushSync();
+		});
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/side-effect-derived-date/main.svelte b/packages/svelte/tests/runtime-runes/samples/side-effect-derived-date/main.svelte
@@ -0,0 +1,27 @@
+<script>
+	import { SvelteDate } from 'svelte/reactivity';
+
+	let visibleExternal = $state(false);
+	let external = new SvelteDate();
+	const throws = $derived.by(() => {
+		external.setTime(12345);
+		return external;
+	})
+
+	let visibleInternal = $state(false);
+	const works = $derived.by(() => {
+		let internal = new SvelteDate();
+		internal.setTime(12345);
+		return internal;
+	})
+</script>
+
+<button onclick={() => (visibleExternal = true)}>external</button>
+{#if visibleExternal}
+	{throws}
+{/if}
+<button onclick={() => (visibleInternal = true)}>internal</button>
+{#if visibleInternal}
+	{works}
+{/if}
+
diff --git a/packages/svelte/tests/runtime-runes/samples/side-effect-derived-url-search-params/_config.js b/packages/svelte/tests/runtime-runes/samples/side-effect-derived-url-search-params/_config.js
@@ -0,0 +1,23 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	compileOptions: {
+		dev: true,
+		runes: true
+	},
+
+	test({ assert, target }) {
+		const [button1, button2] = target.querySelectorAll('button');
+
+		assert.throws(() => {
+			button1?.click();
+			flushSync();
+		}, /state_unsafe_mutation/);
+
+		assert.doesNotThrow(() => {
+			button2?.click();
+			flushSync();
+		});
+	}
+});
diff --git a/...ages/svelte/tests/runtime-runes/samples/side-effect-derived-url-search-params/main.svelte b/...ages/svelte/tests/runtime-runes/samples/side-effect-derived-url-search-params/main.svelte
@@ -0,0 +1,27 @@
+<script>
+	import { SvelteURLSearchParams } from 'svelte/reactivity';
+
+	let visibleExternal = $state(false);
+	let external = new SvelteURLSearchParams();
+	const throws = $derived.by(() => {
+		external.append('foo', 'bar')
+		return external;
+	})
+
+	let visibleInternal = $state(false);
+	const works = $derived.by(() => {
+		let internal = new SvelteURLSearchParams();
+		internal.append('foo', 'bar')
+		return internal;
+	})
+</script>
+
+<button onclick={() => (visibleExternal = true)}>external</button>
+{#if visibleExternal}
+	{throws}
+{/if}
+<button onclick={() => (visibleInternal = true)}>internal</button>
+{#if visibleInternal}
+	{works}
+{/if}
+
diff --git a/packages/svelte/tests/runtime-runes/samples/side-effect-derived-url/_config.js b/packages/svelte/tests/runtime-runes/samples/side-effect-derived-url/_config.js
@@ -0,0 +1,23 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	compileOptions: {
+		dev: true,
+		runes: true
+	},
+
+	test({ assert, target }) {
+		const [button1, button2] = target.querySelectorAll('button');
+
+		assert.throws(() => {
+			button1?.click();
+			flushSync();
+		}, /state_unsafe_mutation/);
+
+		assert.doesNotThrow(() => {
+			button2?.click();
+			flushSync();
+		});
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/side-effect-derived-url/main.svelte b/packages/svelte/tests/runtime-runes/samples/side-effect-derived-url/main.svelte
@@ -0,0 +1,27 @@
+<script>
+	import { SvelteURL } from 'svelte/reactivity';
+
+	let visibleExternal = $state(false);
+	let external = new SvelteURL('https://svelte.dev');
+	const throws = $derived.by(() => {
+		external.host = 'kit.svelte.dev'
+		return external;
+	})
+
+	let visibleInternal = $state(false);
+	const works = $derived.by(() => {
+		let internal = new SvelteURL('https://svelte.dev');
+		internal.host = 'kit.svelte.dev'
+		return internal;
+	})
+</script>
+
+<button onclick={() => (visibleExternal = true)}>external</button>
+{#if visibleExternal}
+	{throws}
+{/if}
+<button onclick={() => (visibleInternal = true)}>internal</button>
+{#if visibleInternal}
+	{works}
+{/if}
+