fix: set deriveds as CLEAN if they are assigned to

Author: paoloricciuti

.changeset/nervous-kids-shake.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: set deriveds as `CLEAN` if they are assigned to

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

@@ -171,6 +171,10 @@ export function internal_set(source, value) {
 			}
 		}
 
+		if ((source.f & DERIVED) !== 0) {
+			set_signal_status(/** @type {Derived} */ (source), CLEAN);
+		}
+
 		mark_reactions(source, DIRTY);
 
 		// It's possible that the current reaction might not have up-to-date dependencies

packages/svelte/tests/signals/test.ts

@@ -1080,6 +1080,21 @@ describe('signals', () => {
 		};
 	});
 
+	test.only("deriveds set after they are DIRTY doesn't get updated on get", () => {
+		return () => {
+			const a = state(0);
+			const b = derived(() => $.get(a));
+
+			set(b, 1);
+			assert.equal($.get(b), 1);
+
+			set(a, 2);
+			set(b, 3);
+
+			assert.equal($.get(b), 3);
+		};
+	});
+
 	test('deriveds containing effects work correctly when used with untrack', () => {
 		return () => {
 			let a = render_effect(() => {});