chore: simplify source ownership (#16333)

* simplify source ownership

* rename

* changeset

* make it unnecessary to hand onto `current_sources` past the initial update

Author: Rich-Harris

.changeset/eight-walls-mate.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+chore: simplify reaction/source ownership tracking

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

@@ -1,6 +1,13 @@
 /** @import { Source } from '#client' */
 import { DEV } from 'esm-env';
-import { get, active_effect, active_reaction, set_active_reaction } from './runtime.js';
+import {
+	get,
+	active_effect,
+	update_version,
+	active_reaction,
+	set_update_version,
+	set_active_reaction
+} from './runtime.js';
 import {
 	array_prototype,
 	get_descriptor,
@@ -41,21 +48,31 @@ export function proxy(value) {
 	var version = source(0);
 
 	var stack = DEV && tracing_mode_flag ? get_stack('CreatedAt') : null;
-	var reaction = active_reaction;
+	var parent_version = update_version;
 
 	/**
 	 * Executes the proxy in the context of the reaction it was originally created in, if any
 	 * @template T
 	 * @param {() => T} fn
 	 */
 	var with_parent = (fn) => {
-		var previous_reaction = active_reaction;
-		set_active_reaction(reaction);
+		if (update_version === parent_version) {
+			return fn();
+		}
+
+		// child source is being created after the initial proxy —
+		// prevent it from being associated with the current reaction
+		var reaction = active_reaction;
+		var version = update_version;
+
+		set_active_reaction(null);
+		set_update_version(parent_version);
 
-		/** @type {T} */
 		var result = fn();
 
-		set_active_reaction(previous_reaction);
+		set_active_reaction(reaction);
+		set_update_version(version);
+
 		return result;
 	};
 

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

@@ -11,7 +11,7 @@ import {
 	untrack,
 	increment_write_version,
 	update_effect,
-	source_ownership,
+	current_sources,
 	check_dirtiness,
 	untracking,
 	is_destroying_effect,
@@ -140,7 +140,7 @@ export function set(source, value, should_proxy = false) {
 		(!untracking || (active_reaction.f & INSPECT_EFFECT) !== 0) &&
 		is_runes() &&
 		(active_reaction.f & (DERIVED | BLOCK_EFFECT | INSPECT_EFFECT)) !== 0 &&
-		!(source_ownership?.reaction === active_reaction && source_ownership.sources.includes(source))
+		!current_sources?.includes(source)
 	) {
 		e.state_unsafe_mutation();
 	}

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

@@ -88,17 +88,17 @@ export function set_active_effect(effect) {
 /**
  * When sources are created within a reaction, reading and writing
  * them within that reaction should not cause a re-run
- * @type {null | { reaction: Reaction, sources: Source[] }}
+ * @type {null | Source[]}
  */
-export let source_ownership = null;
+export let current_sources = null;
 
 /** @param {Value} value */
 export function push_reaction_value(value) {
 	if (active_reaction !== null && active_reaction.f & EFFECT_IS_UPDATING) {
-		if (source_ownership === null) {
-			source_ownership = { reaction: active_reaction, sources: [value] };
+		if (current_sources === null) {
+			current_sources = [value];
 		} else {
-			source_ownership.sources.push(value);
+			current_sources.push(value);
 		}
 	}
 }
@@ -136,6 +136,11 @@ let read_version = 0;
 
 export let update_version = read_version;
 
+/** @param {number} value */
+export function set_update_version(value) {
+	update_version = value;
+}
+
 // If we are working with a get() chain that has no active container,
 // to prevent memory leaks, we skip adding the reaction.
 export let skip_reaction = false;
@@ -236,7 +241,7 @@ function schedule_possible_effect_self_invalidation(signal, effect, root = true)
 	var reactions = signal.reactions;
 	if (reactions === null) return;
 
-	if (source_ownership?.reaction === active_reaction && source_ownership.sources.includes(signal)) {
+	if (current_sources?.includes(signal)) {
 		return;
 	}
 
@@ -263,7 +268,7 @@ export function update_reaction(reaction) {
 	var previous_untracked_writes = untracked_writes;
 	var previous_reaction = active_reaction;
 	var previous_skip_reaction = skip_reaction;
-	var previous_reaction_sources = source_ownership;
+	var previous_sources = current_sources;
 	var previous_component_context = component_context;
 	var previous_untracking = untracking;
 	var previous_update_version = update_version;
@@ -277,7 +282,7 @@ export function update_reaction(reaction) {
 		(flags & UNOWNED) !== 0 && (untracking || !is_updating_effect || active_reaction === null);
 	active_reaction = (flags & (BRANCH_EFFECT | ROOT_EFFECT)) === 0 ? reaction : null;
 
-	source_ownership = null;
+	current_sources = null;
 	set_component_context(reaction.ctx);
 	untracking = false;
 	update_version = ++read_version;
@@ -365,7 +370,7 @@ export function update_reaction(reaction) {
 		untracked_writes = previous_untracked_writes;
 		active_reaction = previous_reaction;
 		skip_reaction = previous_skip_reaction;
-		source_ownership = previous_reaction_sources;
+		current_sources = previous_sources;
 		set_component_context(previous_component_context);
 		untracking = previous_untracking;
 		update_version = previous_update_version;
@@ -759,10 +764,7 @@ export function get(signal) {
 
 	// Register the dependency on the current reaction signal.
 	if (active_reaction !== null && !untracking) {
-		if (
-			source_ownership?.reaction !== active_reaction ||
-			!source_ownership?.sources.includes(signal)
-		) {
+		if (!current_sources?.includes(signal)) {
 			var deps = active_reaction.deps;
 			if (signal.rv < read_version) {
 				signal.rv = read_version;