fix: reconnected deep derived signals to graph (#12350)

* fix: fixed derived disconnected issues

* add test

* changeset

* lint

* refactor

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

Co-authored-by: Rich Harris <rich.harris@vercel.com>

* Update packages/svelte/src/internal/client/runtime.js

Co-authored-by: Rich Harris <rich.harris@vercel.com>

* address feedback

* tweak

* tweak

* simplify

* lint

---------

Co-authored-by: Rich Harris <rich.harris@vercel.com>

.changeset/smart-zoos-vanish.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: reconnected deep derived signals to graph

packages/svelte/src/internal/client/runtime.js

@@ -171,8 +171,17 @@ export function check_dirtiness(reaction) {
 
 		if (dependencies !== null) {
 			var is_unowned = (flags & UNOWNED) !== 0;
+			var i;
+
+			if ((flags & DISCONNECTED) !== 0) {
+				for (i = 0; i < dependencies.length; i++) {
+					(dependencies[i].reactions ??= []).push(reaction);
+				}
 
-			for (var i = 0; i < dependencies.length; i++) {
+				reaction.f ^= DISCONNECTED;
+			}
+
+			for (i = 0; i < dependencies.length; i++) {
 				var dependency = dependencies[i];
 
 				if (check_dirtiness(/** @type {import('#client').Derived} */ (dependency))) {
@@ -771,25 +780,6 @@ export function get(signal) {
 		if (check_dirtiness(derived)) {
 			update_derived(derived);
 		}
-
-		if ((flags & DISCONNECTED) !== 0) {
-			// reconnect to the graph
-			deps = derived.deps;
-
-			if (deps !== null) {
-				for (var i = 0; i < deps.length; i++) {
-					var dep = deps[i];
-					var reactions = dep.reactions;
-					if (reactions === null) {
-						dep.reactions = [derived];
-					} else if (!reactions.includes(derived)) {
-						reactions.push(derived);
-					}
-				}
-			}
-
-			derived.f ^= DISCONNECTED;
-		}
 	}
 
 	return signal.v;

packages/svelte/tests/signals/test.ts

@@ -550,6 +550,40 @@ describe('signals', () => {
 		};
 	});
 
+	test('deriveds update upon reconnection #3', () => {
+		let a = source(false);
+		let b = source(false);
+
+		let c = derived(() => $.get(a) || $.get(b));
+		let d = derived(() => $.get(c));
+		let e = derived(() => $.get(d));
+
+		return () => {
+			const log: string[] = [];
+			let destroy = effect_root(() => {
+				render_effect(() => {
+					$.get(e);
+					log.push('init');
+				});
+			});
+			destroy();
+
+			destroy = effect_root(() => {
+				render_effect(() => {
+					$.get(e);
+					log.push('update');
+				});
+			});
+
+			assert.deepEqual(log, ['init', 'update']);
+
+			set(a, true);
+			flushSync();
+
+			assert.deepEqual(log, ['init', 'update', 'update']);
+		};
+	});
+
 	test('unowned deriveds are not added as reactions', () => {
 		var count = source(0);