From f6a489e172a1634491109dc7c5a63ae548ecadfb Mon Sep 17 00:00:00 2001
From: Dominic Gannaway <trueadm@users.noreply.github.com>
Date: Wed, 29 Jan 2025 09:49:20 +0000
Subject: [PATCH 01/10] fix: improve derived connection to ownership graph

---
 .changeset/blue-rocks-play.md                 |  5 ++
 .../internal/client/reactivity/deriveds.js    |  2 +-
 .../svelte/src/internal/client/runtime.js     | 17 ++--
 packages/svelte/tests/signals/test.ts         | 90 +++++++++++++++----
 4 files changed, 87 insertions(+), 27 deletions(-)
 create mode 100644 .changeset/blue-rocks-play.md

diff --git a/.changeset/blue-rocks-play.md b/.changeset/blue-rocks-play.md
new file mode 100644
index 000000000000..31e99911482c
--- /dev/null
+++ b/.changeset/blue-rocks-play.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: improve derived connection to ownership graph
diff --git a/packages/svelte/src/internal/client/reactivity/deriveds.js b/packages/svelte/src/internal/client/reactivity/deriveds.js
index e86963408ce7..f180a6999574 100644
--- a/packages/svelte/src/internal/client/reactivity/deriveds.js
+++ b/packages/svelte/src/internal/client/reactivity/deriveds.js
@@ -87,7 +87,7 @@ export function derived_safe_equal(fn) {
  * @param {Derived} derived
  * @returns {void}
  */
-function destroy_derived_children(derived) {
+export function destroy_derived_children(derived) {
 	var children = derived.children;
 
 	if (children !== null) {
diff --git a/packages/svelte/src/internal/client/runtime.js b/packages/svelte/src/internal/client/runtime.js
index 859925186f59..87d6b589d7fd 100644
--- a/packages/svelte/src/internal/client/runtime.js
+++ b/packages/svelte/src/internal/client/runtime.js
@@ -28,7 +28,12 @@ import {
 } from './constants.js';
 import { flush_tasks } from './dom/task.js';
 import { internal_set, set } from './reactivity/sources.js';
-import { destroy_derived, execute_derived, update_derived } from './reactivity/deriveds.js';
+import {
+	destroy_derived,
+	destroy_derived_children,
+	execute_derived,
+	update_derived
+} from './reactivity/deriveds.js';
 import * as e from './errors.js';
 import { FILENAME } from '../../constants.js';
 import { legacy_mode_flag, tracing_mode_flag } from '../flags/index.js';
@@ -517,6 +522,8 @@ function remove_reaction(signal, dependency) {
 		if ((dependency.f & (UNOWNED | DISCONNECTED)) === 0) {
 			dependency.f ^= DISCONNECTED;
 		}
+		// Disconnect any reactions owned by this reaction
+		destroy_derived_children(/** @type {Derived} **/ (dependency));
 		remove_reactions(/** @type {Derived} **/ (dependency), 0);
 	}
 }
@@ -934,13 +941,7 @@ export function get(signal) {
 				new_deps.push(signal);
 			}
 		}
-	}
-
-	if (
-		is_derived &&
-		/** @type {Derived} */ (signal).deps === null &&
-		(active_reaction === null || untracking || (active_reaction.f & DERIVED) !== 0)
-	) {
+	} else if (is_derived && /** @type {Derived} */ (signal).deps === null) {
 		var derived = /** @type {Derived} */ (signal);
 		var parent = derived.parent;
 
diff --git a/packages/svelte/tests/signals/test.ts b/packages/svelte/tests/signals/test.ts
index aa1dbf31328c..687e715eb956 100644
--- a/packages/svelte/tests/signals/test.ts
+++ b/packages/svelte/tests/signals/test.ts
@@ -9,11 +9,12 @@ import {
 	user_effect
 } from '../../src/internal/client/reactivity/effects';
 import { state, set } from '../../src/internal/client/reactivity/sources';
-import type { Derived, Value } from '../../src/internal/client/types';
+import type { Derived, Effect, Value } from '../../src/internal/client/types';
 import { proxy } from '../../src/internal/client/proxy';
 import { derived } from '../../src/internal/client/reactivity/deriveds';
 import { snapshot } from '../../src/internal/shared/clone.js';
 import { SvelteSet } from '../../src/reactivity/set';
+import { DESTROYED } from '../../src/internal/client/constants';
 
 /**
  * @param runes runes mode
@@ -256,12 +257,16 @@ describe('signals', () => {
 
 			const a = state(0);
 			const b = state(0);
-			const c = derived(() => {
-				const a_2 = derived(() => $.get(a) + '!');
-				const b_2 = derived(() => $.get(b) + '?');
-				nested.push(a_2, b_2);
+			let c: any;
+
+			const destroy = effect_root(() => {
+				c = derived(() => {
+					const a_2 = derived(() => $.get(a) + '!');
+					const b_2 = derived(() => $.get(b) + '?');
+					nested.push(a_2, b_2);
 
-				return { a: $.get(a_2), b: $.get(b_2) };
+					return { a: $.get(a_2), b: $.get(b_2) };
+				});
 			});
 
 			$.get(c);
@@ -274,11 +279,14 @@ describe('signals', () => {
 
 			$.get(c);
 
-			// Ensure we're not leaking dependencies
-			assert.deepEqual(
-				nested.slice(0, -2).map((s) => s.deps),
-				[null, null, null, null]
-			);
+			// Ensure we're not leaking
+			assert.equal(a.reactions?.[0], nested.at(-2));
+			assert.equal(b.reactions?.[0], nested.at(-1));
+
+			destroy();
+
+			assert.equal(a.reactions, null);
+			assert.equal(b.reactions, null);
 		};
 	});
 
@@ -831,12 +839,54 @@ describe('signals', () => {
 		};
 	});
 
+	test('deriveds containing effects work correctly', () => {
+		return () => {
+			let a = render_effect(() => {});
+			let b = state(0);
+			let c;
+			let effects: Effect[] = [];
+
+			const destroy = effect_root(() => {
+				a = render_effect(() => {
+					c = derived(() => {
+						effects.push(
+							effect(() => {
+								$.get(b);
+							})
+						);
+						$.get(b);
+					});
+					$.get(c);
+				});
+			});
+
+			assert.equal(c!.children?.length, 1);
+			assert.equal(a.first, a.last);
+
+			set(b, 1);
+
+			flushSync();
+
+			assert.equal(c!.children?.length, 1);
+			assert.equal(a.first, a.last);
+
+			destroy();
+
+			assert.equal(a.deriveds, null);
+			assert.equal(a.first, null);
+
+			assert.equal(effects.length, 2);
+			assert.equal((effects[0].f & DESTROYED) !== 0, true);
+			assert.equal((effects[1].f & DESTROYED) !== 0, true);
+		};
+	});
+
 	test('deriveds containing effects work correctly when used with untrack', () => {
 		return () => {
 			let a = render_effect(() => {});
 			let b = state(0);
 			let c;
-			let effects = [];
+			let effects: Effect[] = [];
 
 			const destroy = effect_root(() => {
 				a = render_effect(() => {
@@ -854,20 +904,24 @@ describe('signals', () => {
 				});
 			});
 
-			assert.deepEqual(c!.children?.length, 1);
-			assert.deepEqual(a.first, a.last);
+			assert.equal(c!.children?.length, 1);
+			assert.equal(a.first, a.last);
 
 			set(b, 1);
 
 			flushSync();
 
-			assert.deepEqual(c!.children?.length, 1);
-			assert.deepEqual(a.first, a.last);
+			assert.equal(c!.children?.length, 1);
+			assert.equal(a.first, a.last);
 
 			destroy();
 
-			assert.deepEqual(a.deriveds, null);
-			assert.deepEqual(a.first, null);
+			assert.equal(a.deriveds, null);
+			assert.equal(a.first, null);
+
+			assert.equal(effects.length, 2);
+			assert.equal((effects[0].f & DESTROYED) !== 0, true);
+			assert.equal((effects[1].f & DESTROYED) !== 0, true);
 		};
 	});
 

From 293bdfd721140724c60ddc3a7533fcdfe4423bdf Mon Sep 17 00:00:00 2001
From: Dominic Gannaway <trueadm@users.noreply.github.com>
Date: Wed, 29 Jan 2025 10:52:35 +0000
Subject: [PATCH 02/10] revised

---
 .../svelte/src/internal/client/runtime.js     | 22 ++++---
 packages/svelte/tests/signals/test.ts         | 58 +++++++++++++++++++
 2 files changed, 72 insertions(+), 8 deletions(-)

diff --git a/packages/svelte/src/internal/client/runtime.js b/packages/svelte/src/internal/client/runtime.js
index 87d6b589d7fd..066532fbd5a8 100644
--- a/packages/svelte/src/internal/client/runtime.js
+++ b/packages/svelte/src/internal/client/runtime.js
@@ -414,7 +414,13 @@ export function update_reaction(reaction) {
 	skipped_deps = 0;
 	untracked_writes = null;
 	active_reaction = (flags & (BRANCH_EFFECT | ROOT_EFFECT)) === 0 ? reaction : null;
-	skip_reaction = !is_flushing_effect && (flags & UNOWNED) !== 0;
+	// prettier-ignore
+	skip_reaction =
+		(flags & UNOWNED) !== 0 &&
+		(!is_flushing_effect ||
+				(/** @type {Derived} */ (reaction).parent !== null &&
+				(/** @type {Derived} */ (reaction).parent.f & DERIVED) !== 0));
+
 	derived_sources = null;
 	set_component_context(reaction.ctx);
 	untracking = false;
@@ -946,14 +952,14 @@ export function get(signal) {
 		var parent = derived.parent;
 
 		if (parent !== null) {
-			// Attach the derived to the nearest parent effect or derived
-			if ((parent.f & DERIVED) !== 0) {
-				var parent_derived = /** @type {Derived} */ (parent);
-
-				if (!parent_derived.children?.includes(derived)) {
-					(parent_derived.children ??= []).push(derived);
-				}
+			// If the derived is owned by another derived then mark it as unowned
+			// as the derived value might have been shared and thus we cannot determine
+			// a true
+			if ((parent.f & DERIVED) !== 0 && (parent.f & UNOWNED) === 0) {
+				debugger;
+				derived.f ^= UNOWNED;
 			} else {
+				// Otherwise we can attach the derieved to the parent effect
 				var parent_effect = /** @type {Effect} */ (parent);
 
 				if (!parent_effect.deriveds?.includes(derived)) {
diff --git a/packages/svelte/tests/signals/test.ts b/packages/svelte/tests/signals/test.ts
index 687e715eb956..d09a748bc00d 100644
--- a/packages/svelte/tests/signals/test.ts
+++ b/packages/svelte/tests/signals/test.ts
@@ -538,6 +538,64 @@ describe('signals', () => {
 		};
 	});
 
+	test('mixed nested deriveds correctly cleanup when no longer connected to graph #1', () => {
+		let a: Derived<unknown>;
+		let b: Derived<unknown>;
+		let s = state(0);
+
+		const destroy = effect_root(() => {
+			render_effect(() => {
+				a = derived(() => {
+					b = derived(() => {
+						$.get(s);
+					});
+					$.untrack(() => {
+						$.get(b);
+					});
+					$.get(s);
+				});
+				$.get(a);
+			});
+		});
+
+		return () => {
+			flushSync();
+			assert.equal(a?.deps?.length, 1);
+			assert.equal(s?.reactions?.length, 1);
+			destroy();
+			assert.equal(s?.reactions, null);
+		};
+	});
+
+	test('mixed nested deriveds correctly cleanup when no longer connected to graph #2', () => {
+		let a: Derived<unknown>;
+		let b: Derived<unknown>;
+		let s = state(0);
+
+		const destroy = effect_root(() => {
+			render_effect(() => {
+				a = derived(() => {
+					b = derived(() => {
+						$.get(s);
+					});
+					effect_root(() => {
+						$.get(b);
+					});
+					$.get(s);
+				});
+				$.get(a);
+			});
+		});
+
+		return () => {
+			flushSync();
+			assert.equal(a?.deps?.length, 1);
+			assert.equal(s?.reactions?.length, 1);
+			destroy();
+			assert.equal(s?.reactions, null);
+		};
+	});
+
 	test('deriveds update upon reconnection #1', () => {
 		let a = state(false);
 		let b = state(false);

From bcbba7e19ba07c9e32c48a63be3ff1ecf7216ebd Mon Sep 17 00:00:00 2001
From: Dominic Gannaway <trueadm@users.noreply.github.com>
Date: Wed, 29 Jan 2025 10:54:40 +0000
Subject: [PATCH 03/10] revised

---
 packages/svelte/src/internal/client/runtime.js | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/packages/svelte/src/internal/client/runtime.js b/packages/svelte/src/internal/client/runtime.js
index 066532fbd5a8..613f01338951 100644
--- a/packages/svelte/src/internal/client/runtime.js
+++ b/packages/svelte/src/internal/client/runtime.js
@@ -953,10 +953,9 @@ export function get(signal) {
 
 		if (parent !== null) {
 			// If the derived is owned by another derived then mark it as unowned
-			// as the derived value might have been shared and thus we cannot determine
-			// a true
+			// as the derived value might have been referenced in a different context
+			// since and thus its parent might not be its true owner anymore
 			if ((parent.f & DERIVED) !== 0 && (parent.f & UNOWNED) === 0) {
-				debugger;
 				derived.f ^= UNOWNED;
 			} else {
 				// Otherwise we can attach the derieved to the parent effect

From 91a23e06e48ae414819c12a26a5b476beb380667 Mon Sep 17 00:00:00 2001
From: Dominic Gannaway <trueadm@users.noreply.github.com>
Date: Wed, 29 Jan 2025 11:12:08 +0000
Subject: [PATCH 04/10] revised

---
 .../svelte/src/internal/client/runtime.js     |  6 ++-
 packages/svelte/tests/signals/test.ts         | 44 ++++++++++++++++++-
 2 files changed, 47 insertions(+), 3 deletions(-)

diff --git a/packages/svelte/src/internal/client/runtime.js b/packages/svelte/src/internal/client/runtime.js
index 613f01338951..a870e93c0eb9 100644
--- a/packages/svelte/src/internal/client/runtime.js
+++ b/packages/svelte/src/internal/client/runtime.js
@@ -418,8 +418,12 @@ export function update_reaction(reaction) {
 	skip_reaction =
 		(flags & UNOWNED) !== 0 &&
 		(!is_flushing_effect ||
+			// If we were previously not in a reactive context and we're reading an unowned derived
+			// that was created inside another derived, then we don't fully know the real owner and thus
+			// we need to skip adding any reactions for this unowned
+				((previous_reaction === null || previous_untracking) &&
 				(/** @type {Derived} */ (reaction).parent !== null &&
-				(/** @type {Derived} */ (reaction).parent.f & DERIVED) !== 0));
+				(/** @type {Derived} */ (reaction).parent.f & DERIVED) !== 0)));
 
 	derived_sources = null;
 	set_component_context(reaction.ctx);
diff --git a/packages/svelte/tests/signals/test.ts b/packages/svelte/tests/signals/test.ts
index d09a748bc00d..b7ab101bc3dc 100644
--- a/packages/svelte/tests/signals/test.ts
+++ b/packages/svelte/tests/signals/test.ts
@@ -69,7 +69,7 @@ describe('signals', () => {
 		};
 	});
 
-	test('multiple effects with state and derived in it#1', () => {
+	test('multiple effects with state and derived in it #1', () => {
 		const log: string[] = [];
 
 		let count = state(0);
@@ -90,7 +90,7 @@ describe('signals', () => {
 		};
 	});
 
-	test('multiple effects with state and derived in it#2', () => {
+	test('multiple effects with state and derived in it #2', () => {
 		const log: string[] = [];
 
 		let count = state(0);
@@ -596,6 +596,46 @@ describe('signals', () => {
 		};
 	});
 
+	test('mixed nested deriveds correctly cleanup when no longer connected to graph #3', () => {
+		let a: Derived<unknown>;
+		let b: Derived<unknown>;
+		let s = state(0);
+		let logs: any[] = [];
+
+		const destroy = effect_root(() => {
+			render_effect(() => {
+				a = derived(() => {
+					b = derived(() => {
+						return $.get(s);
+					});
+					effect_root(() => {
+						$.get(b);
+					});
+					render_effect(() => {
+						debugger
+						logs.push($.get(b));
+					});
+					$.get(s);
+				});
+				$.get(a);
+			});
+		});
+
+		return () => {
+			flushSync();
+			assert.equal(a?.deps?.length, 1);
+			assert.equal(s?.reactions?.length, 2);
+
+			set(s, 1);
+			flushSync();
+
+			assert.deepEqual(logs, [0, 1]);
+
+			destroy();
+			assert.equal(s?.reactions, null);
+		};
+	});
+
 	test('deriveds update upon reconnection #1', () => {
 		let a = state(false);
 		let b = state(false);

From 679929a5158407a5167ebf7abc7a3b71ac6559b8 Mon Sep 17 00:00:00 2001
From: Dominic Gannaway <trueadm@users.noreply.github.com>
Date: Wed, 29 Jan 2025 11:16:17 +0000
Subject: [PATCH 05/10] revised

---
 packages/svelte/tests/signals/test.ts | 1 -
 1 file changed, 1 deletion(-)

diff --git a/packages/svelte/tests/signals/test.ts b/packages/svelte/tests/signals/test.ts
index b7ab101bc3dc..04cf2b4550bd 100644
--- a/packages/svelte/tests/signals/test.ts
+++ b/packages/svelte/tests/signals/test.ts
@@ -612,7 +612,6 @@ describe('signals', () => {
 						$.get(b);
 					});
 					render_effect(() => {
-						debugger
 						logs.push($.get(b));
 					});
 					$.get(s);

From 927f3d2acc4665afad036a5bfd9b7bd9e6a8c77f Mon Sep 17 00:00:00 2001
From: Dominic Gannaway <trueadm@users.noreply.github.com>
Date: Wed, 29 Jan 2025 12:15:41 +0000
Subject: [PATCH 06/10] feedback

---
 .../internal/client/reactivity/deriveds.js    | 42 ++++++++-----------
 .../src/internal/client/reactivity/effects.js |  4 +-
 .../src/internal/client/reactivity/types.d.ts |  4 +-
 .../svelte/src/internal/client/runtime.js     | 18 +++++---
 packages/svelte/tests/signals/test.ts         | 10 ++---
 5 files changed, 39 insertions(+), 39 deletions(-)

diff --git a/packages/svelte/src/internal/client/reactivity/deriveds.js b/packages/svelte/src/internal/client/reactivity/deriveds.js
index f180a6999574..1f65ff38c351 100644
--- a/packages/svelte/src/internal/client/reactivity/deriveds.js
+++ b/packages/svelte/src/internal/client/reactivity/deriveds.js
@@ -35,8 +35,12 @@ import { component_context } from '../context.js';
 /*#__NO_SIDE_EFFECTS__*/
 export function derived(fn) {
 	var flags = DERIVED | DIRTY;
+	var parent_derived =
+		active_reaction !== null && (active_reaction.f & DERIVED) !== 0
+			? /** @type {Derived} */ (active_reaction)
+			: null;
 
-	if (active_effect === null) {
+	if (active_effect === null || (parent_derived !== null && (parent_derived.f & UNOWNED) !== 0)) {
 		flags |= UNOWNED;
 	} else {
 		// Since deriveds are evaluated lazily, any effects created inside them are
@@ -44,16 +48,11 @@ export function derived(fn) {
 		active_effect.f |= EFFECT_HAS_DERIVED;
 	}
 
-	var parent_derived =
-		active_reaction !== null && (active_reaction.f & DERIVED) !== 0
-			? /** @type {Derived} */ (active_reaction)
-			: null;
-
 	/** @type {Derived<V>} */
 	const signal = {
-		children: null,
 		ctx: component_context,
 		deps: null,
+		effects: null,
 		equals,
 		f: flags,
 		fn,
@@ -87,19 +86,14 @@ export function derived_safe_equal(fn) {
  * @param {Derived} derived
  * @returns {void}
  */
-export function destroy_derived_children(derived) {
-	var children = derived.children;
-
-	if (children !== null) {
-		derived.children = null;
-
-		for (var i = 0; i < children.length; i += 1) {
-			var child = children[i];
-			if ((child.f & DERIVED) !== 0) {
-				destroy_derived(/** @type {Derived} */ (child));
-			} else {
-				destroy_effect(/** @type {Effect} */ (child));
-			}
+export function destroy_derived_effects(derived) {
+	var effects = derived.effects;
+
+	if (effects !== null) {
+		derived.effects = null;
+
+		for (var i = 0; i < effects.length; i += 1) {
+			destroy_effect(/** @type {Effect} */ (effects[i]));
 		}
 	}
 }
@@ -147,7 +141,7 @@ export function execute_derived(derived) {
 
 			stack.push(derived);
 
-			destroy_derived_children(derived);
+			destroy_derived_effects(derived);
 			value = update_reaction(derived);
 		} finally {
 			set_active_effect(prev_active_effect);
@@ -156,7 +150,7 @@ export function execute_derived(derived) {
 		}
 	} else {
 		try {
-			destroy_derived_children(derived);
+			destroy_derived_effects(derived);
 			value = update_reaction(derived);
 		} finally {
 			set_active_effect(prev_active_effect);
@@ -188,9 +182,9 @@ export function update_derived(derived) {
  * @returns {void}
  */
 export function destroy_derived(derived) {
-	destroy_derived_children(derived);
+	destroy_derived_effects(derived);
 	remove_reactions(derived, 0);
 	set_signal_status(derived, DESTROYED);
 
-	derived.v = derived.children = derived.deps = derived.ctx = derived.reactions = null;
+	derived.v = derived.deps = derived.ctx = derived.reactions = null;
 }
diff --git a/packages/svelte/src/internal/client/reactivity/effects.js b/packages/svelte/src/internal/client/reactivity/effects.js
index 8a7cffecd623..1ccc2b4b6173 100644
--- a/packages/svelte/src/internal/client/reactivity/effects.js
+++ b/packages/svelte/src/internal/client/reactivity/effects.js
@@ -53,7 +53,7 @@ export function validate_effect(rune) {
 		e.effect_orphan(rune);
 	}
 
-	if (active_reaction !== null && (active_reaction.f & UNOWNED) !== 0) {
+	if (active_reaction !== null && (active_reaction.f & UNOWNED) !== 0 && active_effect === null) {
 		e.effect_in_unowned_derived();
 	}
 
@@ -153,7 +153,7 @@ function create_effect(type, fn, sync, push = true) {
 		// if we're in a derived, add the effect there too
 		if (active_reaction !== null && (active_reaction.f & DERIVED) !== 0) {
 			var derived = /** @type {Derived} */ (active_reaction);
-			(derived.children ??= []).push(effect);
+			(derived.effects ??= []).push(effect);
 		}
 	}
 
diff --git a/packages/svelte/src/internal/client/reactivity/types.d.ts b/packages/svelte/src/internal/client/reactivity/types.d.ts
index 3a76a3ff836c..d992f840b5b5 100644
--- a/packages/svelte/src/internal/client/reactivity/types.d.ts
+++ b/packages/svelte/src/internal/client/reactivity/types.d.ts
@@ -36,8 +36,8 @@ export interface Reaction extends Signal {
 export interface Derived<V = unknown> extends Value<V>, Reaction {
 	/** The derived function */
 	fn: () => V;
-	/** Reactions created inside this signal */
-	children: null | Reaction[];
+	/** Effects created inside this signal */
+	effects: null | Effect[];
 	/** Parent effect or derived */
 	parent: Effect | Derived | null;
 }
diff --git a/packages/svelte/src/internal/client/runtime.js b/packages/svelte/src/internal/client/runtime.js
index a870e93c0eb9..e32ff60ca514 100644
--- a/packages/svelte/src/internal/client/runtime.js
+++ b/packages/svelte/src/internal/client/runtime.js
@@ -30,7 +30,7 @@ import { flush_tasks } from './dom/task.js';
 import { internal_set, set } from './reactivity/sources.js';
 import {
 	destroy_derived,
-	destroy_derived_children,
+	destroy_derived_effects,
 	execute_derived,
 	update_derived
 } from './reactivity/deriveds.js';
@@ -419,11 +419,10 @@ export function update_reaction(reaction) {
 		(flags & UNOWNED) !== 0 &&
 		(!is_flushing_effect ||
 			// If we were previously not in a reactive context and we're reading an unowned derived
-			// that was created inside another derived, then we don't fully know the real owner and thus
+			// that was created inside another reaction, then we don't fully know the real owner and thus
 			// we need to skip adding any reactions for this unowned
 				((previous_reaction === null || previous_untracking) &&
-				(/** @type {Derived} */ (reaction).parent !== null &&
-				(/** @type {Derived} */ (reaction).parent.f & DERIVED) !== 0)));
+				/** @type {Derived} */ (reaction).parent !== null));
 
 	derived_sources = null;
 	set_component_context(reaction.ctx);
@@ -533,7 +532,7 @@ function remove_reaction(signal, dependency) {
 			dependency.f ^= DISCONNECTED;
 		}
 		// Disconnect any reactions owned by this reaction
-		destroy_derived_children(/** @type {Derived} **/ (dependency));
+		destroy_derived_effects(/** @type {Derived} **/ (dependency));
 		remove_reactions(/** @type {Derived} **/ (dependency), 0);
 	}
 }
@@ -951,11 +950,18 @@ export function get(signal) {
 				new_deps.push(signal);
 			}
 		}
-	} else if (is_derived && /** @type {Derived} */ (signal).deps === null) {
+	} else if (
+		is_derived &&
+		/** @type {Derived} */ (signal).deps === null &&
+		/** @type {Derived} */ (signal).effects === null
+	) {
 		var derived = /** @type {Derived} */ (signal);
 		var parent = derived.parent;
 
 		if (parent !== null) {
+			// if ((parent.f & UNOWNED) === 0) {
+			// 	derived.f ^= UNOWNED;
+			// }
 			// If the derived is owned by another derived then mark it as unowned
 			// as the derived value might have been referenced in a different context
 			// since and thus its parent might not be its true owner anymore
diff --git a/packages/svelte/tests/signals/test.ts b/packages/svelte/tests/signals/test.ts
index 04cf2b4550bd..b062b3d7ef35 100644
--- a/packages/svelte/tests/signals/test.ts
+++ b/packages/svelte/tests/signals/test.ts
@@ -928,7 +928,7 @@ describe('signals', () => {
 			});
 
 			assert.deepEqual(a.deriveds?.length, 1);
-			assert.deepEqual(b?.children, null);
+			assert.deepEqual(b?.effects, null);
 
 			destroy();
 
@@ -957,14 +957,14 @@ describe('signals', () => {
 				});
 			});
 
-			assert.equal(c!.children?.length, 1);
+			assert.equal(c!.effects?.length, 1);
 			assert.equal(a.first, a.last);
 
 			set(b, 1);
 
 			flushSync();
 
-			assert.equal(c!.children?.length, 1);
+			assert.equal(c!.effects?.length, 1);
 			assert.equal(a.first, a.last);
 
 			destroy();
@@ -1001,14 +1001,14 @@ describe('signals', () => {
 				});
 			});
 
-			assert.equal(c!.children?.length, 1);
+			assert.equal(c!.effects?.length, 1);
 			assert.equal(a.first, a.last);
 
 			set(b, 1);
 
 			flushSync();
 
-			assert.equal(c!.children?.length, 1);
+			assert.equal(c!.effects?.length, 1);
 			assert.equal(a.first, a.last);
 
 			destroy();

From 3b85e10ad26a5eed42164ba3f9c79f75bb9dfa01 Mon Sep 17 00:00:00 2001
From: Dominic Gannaway <trueadm@users.noreply.github.com>
Date: Wed, 29 Jan 2025 12:22:19 +0000
Subject: [PATCH 07/10] feedback

---
 packages/svelte/src/internal/client/runtime.js | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/packages/svelte/src/internal/client/runtime.js b/packages/svelte/src/internal/client/runtime.js
index e32ff60ca514..1f8e4b79526a 100644
--- a/packages/svelte/src/internal/client/runtime.js
+++ b/packages/svelte/src/internal/client/runtime.js
@@ -959,9 +959,6 @@ export function get(signal) {
 		var parent = derived.parent;
 
 		if (parent !== null) {
-			// if ((parent.f & UNOWNED) === 0) {
-			// 	derived.f ^= UNOWNED;
-			// }
 			// If the derived is owned by another derived then mark it as unowned
 			// as the derived value might have been referenced in a different context
 			// since and thus its parent might not be its true owner anymore

From 8fdb80c2f1a7942bae7ff67c97ece7657648e36a Mon Sep 17 00:00:00 2001
From: Dominic Gannaway <trueadm@users.noreply.github.com>
Date: Wed, 29 Jan 2025 12:22:34 +0000
Subject: [PATCH 08/10] invasive change

---
 .../src/internal/client/reactivity/effects.js | 18 ------
 .../src/internal/client/reactivity/types.d.ts |  2 -
 .../svelte/src/internal/client/runtime.js     | 11 +---
 packages/svelte/tests/signals/test.ts         | 61 +------------------
 4 files changed, 2 insertions(+), 90 deletions(-)

diff --git a/packages/svelte/src/internal/client/reactivity/effects.js b/packages/svelte/src/internal/client/reactivity/effects.js
index 1ccc2b4b6173..d014ff793dea 100644
--- a/packages/svelte/src/internal/client/reactivity/effects.js
+++ b/packages/svelte/src/internal/client/reactivity/effects.js
@@ -99,7 +99,6 @@ function create_effect(type, fn, sync, push = true) {
 	var effect = {
 		ctx: component_context,
 		deps: null,
-		deriveds: null,
 		nodes_start: null,
 		nodes_end: null,
 		f: type | DIRTY,
@@ -395,22 +394,6 @@ export function execute_effect_teardown(effect) {
 	}
 }
 
-/**
- * @param {Effect} signal
- * @returns {void}
- */
-export function destroy_effect_deriveds(signal) {
-	var deriveds = signal.deriveds;
-
-	if (deriveds !== null) {
-		signal.deriveds = null;
-
-		for (var i = 0; i < deriveds.length; i += 1) {
-			destroy_derived(deriveds[i]);
-		}
-	}
-}
-
 /**
  * @param {Effect} signal
  * @param {boolean} remove_dom
@@ -468,7 +451,6 @@ export function destroy_effect(effect, remove_dom = true) {
 	}
 
 	destroy_effect_children(effect, remove_dom && !removed);
-	destroy_effect_deriveds(effect);
 	remove_reactions(effect, 0);
 	set_signal_status(effect, DESTROYED);
 
diff --git a/packages/svelte/src/internal/client/reactivity/types.d.ts b/packages/svelte/src/internal/client/reactivity/types.d.ts
index d992f840b5b5..5ef0097649a4 100644
--- a/packages/svelte/src/internal/client/reactivity/types.d.ts
+++ b/packages/svelte/src/internal/client/reactivity/types.d.ts
@@ -51,8 +51,6 @@ export interface Effect extends Reaction {
 	 */
 	nodes_start: null | TemplateNode;
 	nodes_end: null | TemplateNode;
-	/** Reactions created inside this signal */
-	deriveds: null | Derived[];
 	/** The effect function */
 	fn: null | (() => void | (() => void));
 	/** The teardown function returned from the effect function */
diff --git a/packages/svelte/src/internal/client/runtime.js b/packages/svelte/src/internal/client/runtime.js
index 1f8e4b79526a..2c53ac8f7b84 100644
--- a/packages/svelte/src/internal/client/runtime.js
+++ b/packages/svelte/src/internal/client/runtime.js
@@ -4,7 +4,6 @@ import { define_property, get_descriptors, get_prototype_of, index_of } from '..
 import {
 	destroy_block_effect_children,
 	destroy_effect_children,
-	destroy_effect_deriveds,
 	execute_effect_teardown,
 	unlink_effect
 } from './reactivity/effects.js';
@@ -580,7 +579,6 @@ export function update_effect(effect) {
 		} else {
 			destroy_effect_children(effect);
 		}
-		destroy_effect_deriveds(effect);
 
 		execute_effect_teardown(effect);
 		var teardown = update_reaction(effect);
@@ -962,15 +960,8 @@ export function get(signal) {
 			// If the derived is owned by another derived then mark it as unowned
 			// as the derived value might have been referenced in a different context
 			// since and thus its parent might not be its true owner anymore
-			if ((parent.f & DERIVED) !== 0 && (parent.f & UNOWNED) === 0) {
+			if ((parent.f & UNOWNED) === 0) {
 				derived.f ^= UNOWNED;
-			} else {
-				// Otherwise we can attach the derieved to the parent effect
-				var parent_effect = /** @type {Effect} */ (parent);
-
-				if (!parent_effect.deriveds?.includes(derived)) {
-					(parent_effect.deriveds ??= []).push(derived);
-				}
 			}
 		}
 	}
diff --git a/packages/svelte/tests/signals/test.ts b/packages/svelte/tests/signals/test.ts
index b062b3d7ef35..edb26fba15d9 100644
--- a/packages/svelte/tests/signals/test.ts
+++ b/packages/svelte/tests/signals/test.ts
@@ -279,10 +279,6 @@ describe('signals', () => {
 
 			$.get(c);
 
-			// Ensure we're not leaking
-			assert.equal(a.reactions?.[0], nested.at(-2));
-			assert.equal(b.reactions?.[0], nested.at(-1));
-
 			destroy();
 
 			assert.equal(a.reactions, null);
@@ -511,7 +507,7 @@ describe('signals', () => {
 				set(inner, 2);
 				$.get(a);
 			});
-			assert.deepEqual(log, ['inner', 2]);
+			assert.deepEqual(log, ['outer', 1, 'inner', 2]);
 			destroy();
 		};
 	});
@@ -883,59 +879,6 @@ describe('signals', () => {
 		};
 	});
 
-	test('nested deriveds clean up the relationships when used with untrack', () => {
-		return () => {
-			let a = render_effect(() => {});
-
-			const destroy = effect_root(() => {
-				a = render_effect(() => {
-					$.untrack(() => {
-						const b = derived(() => {
-							const c = derived(() => {});
-							$.untrack(() => {
-								$.get(c);
-							});
-						});
-						$.get(b);
-					});
-				});
-			});
-
-			assert.deepEqual(a.deriveds?.length, 1);
-
-			destroy();
-
-			assert.deepEqual(a.deriveds, null);
-		};
-	});
-
-	test('nested deriveds do not connect inside parent deriveds if unused', () => {
-		return () => {
-			let a = render_effect(() => {});
-			let b: Derived<void> | undefined;
-
-			const destroy = effect_root(() => {
-				a = render_effect(() => {
-					$.untrack(() => {
-						b = derived(() => {
-							derived(() => {});
-							derived(() => {});
-							derived(() => {});
-						});
-						$.get(b);
-					});
-				});
-			});
-
-			assert.deepEqual(a.deriveds?.length, 1);
-			assert.deepEqual(b?.effects, null);
-
-			destroy();
-
-			assert.deepEqual(a.deriveds, null);
-		};
-	});
-
 	test('deriveds containing effects work correctly', () => {
 		return () => {
 			let a = render_effect(() => {});
@@ -969,7 +912,6 @@ describe('signals', () => {
 
 			destroy();
 
-			assert.equal(a.deriveds, null);
 			assert.equal(a.first, null);
 
 			assert.equal(effects.length, 2);
@@ -1013,7 +955,6 @@ describe('signals', () => {
 
 			destroy();
 
-			assert.equal(a.deriveds, null);
 			assert.equal(a.first, null);
 
 			assert.equal(effects.length, 2);

From adad37b716424a207698953a99c1e2f0efc45cdd Mon Sep 17 00:00:00 2001
From: Dominic Gannaway <trueadm@users.noreply.github.com>
Date: Wed, 29 Jan 2025 12:43:31 +0000
Subject: [PATCH 09/10] fix bugs

---
 packages/svelte/src/internal/client/runtime.js        |  3 +++
 .../samples/derived-unowned-7/_config.js              | 11 ++++++++++-
 packages/svelte/tests/signals/test.ts                 |  2 +-
 3 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/packages/svelte/src/internal/client/runtime.js b/packages/svelte/src/internal/client/runtime.js
index 2c53ac8f7b84..6dd253c0b535 100644
--- a/packages/svelte/src/internal/client/runtime.js
+++ b/packages/svelte/src/internal/client/runtime.js
@@ -216,6 +216,9 @@ export function check_dirtiness(reaction) {
 				}
 
 				if (dependency.wv > reaction.wv) {
+					if (is_unowned) {
+						reaction.wv = dependency.wv;
+					}
 					return true;
 				}
 			}
diff --git a/packages/svelte/tests/runtime-runes/samples/derived-unowned-7/_config.js b/packages/svelte/tests/runtime-runes/samples/derived-unowned-7/_config.js
index 53ca29f4c3f0..bbb24f5e1cef 100644
--- a/packages/svelte/tests/runtime-runes/samples/derived-unowned-7/_config.js
+++ b/packages/svelte/tests/runtime-runes/samples/derived-unowned-7/_config.js
@@ -9,6 +9,15 @@ export default test({
 			btn1.click();
 		});
 
-		assert.deepEqual(logs, ['computing C', 'computing B', 'a', 'foo', 'computing B', 'aaa', 'foo']);
+		assert.deepEqual(logs, [
+			'computing C',
+			'computing B',
+			'a',
+			'foo',
+			'computing B',
+			'aaa',
+			'computing C'
+			'foo'
+		]);
 	}
 });
diff --git a/packages/svelte/tests/signals/test.ts b/packages/svelte/tests/signals/test.ts
index edb26fba15d9..b9fee3b46a52 100644
--- a/packages/svelte/tests/signals/test.ts
+++ b/packages/svelte/tests/signals/test.ts
@@ -507,7 +507,7 @@ describe('signals', () => {
 				set(inner, 2);
 				$.get(a);
 			});
-			assert.deepEqual(log, ['outer', 1, 'inner', 2]);
+			assert.deepEqual(log, ['inner', 2]);
 			destroy();
 		};
 	});

From 7f01dc3a8c23b746e51a1ae36927f88907c28faa Mon Sep 17 00:00:00 2001
From: Dominic Gannaway <trueadm@users.noreply.github.com>
Date: Wed, 29 Jan 2025 13:09:28 +0000
Subject: [PATCH 10/10] fix other bug

---
 packages/svelte/src/internal/client/runtime.js        |  3 ---
 .../samples/derived-unowned-7/_config.js              | 11 +----------
 packages/svelte/tests/signals/test.ts                 |  1 +
 3 files changed, 2 insertions(+), 13 deletions(-)

diff --git a/packages/svelte/src/internal/client/runtime.js b/packages/svelte/src/internal/client/runtime.js
index 6dd253c0b535..2c53ac8f7b84 100644
--- a/packages/svelte/src/internal/client/runtime.js
+++ b/packages/svelte/src/internal/client/runtime.js
@@ -216,9 +216,6 @@ export function check_dirtiness(reaction) {
 				}
 
 				if (dependency.wv > reaction.wv) {
-					if (is_unowned) {
-						reaction.wv = dependency.wv;
-					}
 					return true;
 				}
 			}
diff --git a/packages/svelte/tests/runtime-runes/samples/derived-unowned-7/_config.js b/packages/svelte/tests/runtime-runes/samples/derived-unowned-7/_config.js
index bbb24f5e1cef..53ca29f4c3f0 100644
--- a/packages/svelte/tests/runtime-runes/samples/derived-unowned-7/_config.js
+++ b/packages/svelte/tests/runtime-runes/samples/derived-unowned-7/_config.js
@@ -9,15 +9,6 @@ export default test({
 			btn1.click();
 		});
 
-		assert.deepEqual(logs, [
-			'computing C',
-			'computing B',
-			'a',
-			'foo',
-			'computing B',
-			'aaa',
-			'computing C'
-			'foo'
-		]);
+		assert.deepEqual(logs, ['computing C', 'computing B', 'a', 'foo', 'computing B', 'aaa', 'foo']);
 	}
 });
diff --git a/packages/svelte/tests/signals/test.ts b/packages/svelte/tests/signals/test.ts
index b9fee3b46a52..2ce624a7772e 100644
--- a/packages/svelte/tests/signals/test.ts
+++ b/packages/svelte/tests/signals/test.ts
@@ -481,6 +481,7 @@ describe('signals', () => {
 					effect(() => {
 						log.push('inner', $.get(inner));
 					});
+					return $.get(outer);
 				});
 			});
 		});