From 6636f748ae770e905ca9e88e9a921b4bc854164c Mon Sep 17 00:00:00 2001
From: 7nik <kfiiranet@gmail.com>
Date: Sat, 14 Jun 2025 18:19:42 +0300
Subject: [PATCH] fix: prevent memory leaking signals in legacy mode (#16145)

* fix: prevent memory leaking signals in legacy mode

* format

* fix

---------

Co-authored-by: 7nik <kifiranet@gmail.com>
---
 .changeset/soft-oranges-approve.md                        | 5 +++++
 packages/svelte/src/internal/client/dom/blocks/await.js   | 6 ++++--
 packages/svelte/src/internal/client/dom/blocks/each.js    | 2 +-
 packages/svelte/src/internal/client/reactivity/sources.js | 4 ++--
 packages/svelte/src/legacy/legacy-client.js               | 2 +-
 5 files changed, 13 insertions(+), 6 deletions(-)
 create mode 100644 .changeset/soft-oranges-approve.md

diff --git a/.changeset/soft-oranges-approve.md b/.changeset/soft-oranges-approve.md
new file mode 100644
index 0000000000..f759c128c0
--- /dev/null
+++ b/.changeset/soft-oranges-approve.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: prevent memory leaking signals in legacy mode
diff --git a/packages/svelte/src/internal/client/dom/blocks/await.js b/packages/svelte/src/internal/client/dom/blocks/await.js
index 99bdc0000c..47df5fc9a5 100644
--- a/packages/svelte/src/internal/client/dom/blocks/await.js
+++ b/packages/svelte/src/internal/client/dom/blocks/await.js
@@ -58,8 +58,10 @@ export function await_block(node, get_input, pending_fn, then_fn, catch_fn) {
 	/** @type {Effect | null} */
 	var catch_effect;
 
-	var input_source = (runes ? source : mutable_source)(/** @type {V} */ (undefined));
-	var error_source = (runes ? source : mutable_source)(undefined);
+	var input_source = runes
+		? source(/** @type {V} */ (undefined))
+		: mutable_source(/** @type {V} */ (undefined), false, false);
+	var error_source = runes ? source(undefined) : mutable_source(undefined, false, false);
 	var resolved = false;
 
 	/**
diff --git a/packages/svelte/src/internal/client/dom/blocks/each.js b/packages/svelte/src/internal/client/dom/blocks/each.js
index 954dcb2214..b638a6d2da 100644
--- a/packages/svelte/src/internal/client/dom/blocks/each.js
+++ b/packages/svelte/src/internal/client/dom/blocks/each.js
@@ -521,7 +521,7 @@ function create_item(
 	var reactive = (flags & EACH_ITEM_REACTIVE) !== 0;
 	var mutable = (flags & EACH_ITEM_IMMUTABLE) === 0;
 
-	var v = reactive ? (mutable ? mutable_source(value) : source(value)) : value;
+	var v = reactive ? (mutable ? mutable_source(value, false, false) : source(value)) : value;
 	var i = (flags & EACH_INDEX_REACTIVE) === 0 ? index : source(index);
 
 	if (DEV && reactive) {
diff --git a/packages/svelte/src/internal/client/reactivity/sources.js b/packages/svelte/src/internal/client/reactivity/sources.js
index 40a3e4e77f..56f4138252 100644
--- a/packages/svelte/src/internal/client/reactivity/sources.js
+++ b/packages/svelte/src/internal/client/reactivity/sources.js
@@ -97,7 +97,7 @@ export function state(v, stack) {
  * @returns {Source<V>}
  */
 /*#__NO_SIDE_EFFECTS__*/
-export function mutable_source(initial_value, immutable = false) {
+export function mutable_source(initial_value, immutable = false, trackable = true) {
 	const s = source(initial_value);
 	if (!immutable) {
 		s.equals = safe_equals;
@@ -105,7 +105,7 @@ export function mutable_source(initial_value, immutable = false) {
 
 	// bind the signal to the component context, in case we need to
 	// track updates to trigger beforeUpdate/afterUpdate callbacks
-	if (legacy_mode_flag && component_context !== null && component_context.l !== null) {
+	if (legacy_mode_flag && trackable && component_context !== null && component_context.l !== null) {
 		(component_context.l.s ??= []).push(s);
 	}
 
diff --git a/packages/svelte/src/legacy/legacy-client.js b/packages/svelte/src/legacy/legacy-client.js
index bb9a5a9c03..45c478ecab 100644
--- a/packages/svelte/src/legacy/legacy-client.js
+++ b/packages/svelte/src/legacy/legacy-client.js
@@ -82,7 +82,7 @@ class Svelte4Component {
 		 * @param {unknown} value
 		 */
 		var add_source = (key, value) => {
-			var s = mutable_source(value);
+			var s = mutable_source(value, false, false);
 			sources.set(key, s);
 			return s;
 		};