fix: allow $.state and $.derived to be treeshaken (#15702)

Author: Rich-Harris

.changeset/clever-news-enjoy.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: allow `$.state` and `$.derived` to be treeshaken

packages/svelte/src/internal/client/reactivity/deriveds.js

@@ -67,6 +67,7 @@ export function derived(fn) {
  * @param {() => V} fn
  * @returns {Derived<V>}
  */
+/*#__NO_SIDE_EFFECTS__*/
 export function user_derived(fn) {
 	const d = derived(fn);
 

packages/svelte/src/internal/client/reactivity/sources.js

@@ -78,6 +78,7 @@ export function source(v, stack) {
  * @param {V} v
  * @param {Error | null} [stack]
  */
+/*#__NO_SIDE_EFFECTS__*/
 export function state(v, stack) {
 	const s = source(v, stack);