distinguish between source and mutable_source

packages/svelte/src/compiler/phases/3-transform/client/transform-client.js

@@ -175,7 +175,7 @@ export function client_component(source, analysis, options) {
 
 	for (const [name, binding] of analysis.instance.scope.declarations) {
 		if (binding.kind === 'legacy_reactive') {
-			legacy_reactive_declarations.push(b.const(name, b.call('$.source')));
+			legacy_reactive_declarations.push(b.const(name, b.call('$.mutable_source')));
 		}
 		if (binding.kind === 'store_sub') {
 			if (store_setup.length === 0) {

packages/svelte/src/compiler/phases/3-transform/client/utils.js

@@ -347,7 +347,7 @@ export function serialize_hoistable_params(node, context) {
  */
 export function get_props_method(binding, state, name, default_value) {
 	/** @type {import('estree').Expression[]} */
-	const args = [b.id('$$props'), b.literal(name)];
+	const args = [b.id('$$props'), b.literal(name), b.literal(state.analysis.immutable)];
 
 	if (default_value) {
 		// To avoid eagerly evaluating the right-hand-side, we wrap it in a thunk if necessary
@@ -382,7 +382,7 @@ export function get_props_method(binding, state, name, default_value) {
 export function create_state_declarators(declarator, scope, value) {
 	// in the simple `let count = $state(0)` case, we rewrite `$state` as `$.source`
 	if (declarator.id.type === 'Identifier') {
-		return [b.declarator(declarator.id, b.call('$.source', value))];
+		return [b.declarator(declarator.id, b.call('$.mutable_source', value))];
 	}
 
 	const tmp = scope.generate('tmp');
@@ -392,7 +392,10 @@ export function create_state_declarators(declarator, scope, value) {
 		...paths.map((path) => {
 			const value = path.expression?.(b.id(tmp));
 			const binding = scope.get(/** @type {import('estree').Identifier} */ (path.node).name);
-			return b.declarator(path.node, binding?.kind === 'state' ? b.call('$.source', value) : value);
+			return b.declarator(
+				path.node,
+				binding?.kind === 'state' ? b.call('$.mutable_source', value) : value
+			);
 		})
 	];
 }

packages/svelte/src/compiler/phases/3-transform/client/visitors/template.js

@@ -27,6 +27,7 @@ import {
 	DOMBooleanAttributes,
 	EACH_INDEX_REACTIVE,
 	EACH_IS_CONTROLLED,
+	EACH_IS_IMMUTABLE,
 	EACH_ITEM_REACTIVE,
 	EACH_KEYED
 } from '../../../../../constants.js';
@@ -2117,14 +2118,13 @@ export const template_visitors = {
 		// array or use nested reactivity through runes.
 		// TODO this feels a bit "hidden performance boost"-style, investigate if there's a way
 		// to make this apply in more cases
-		/** @type {number} */
+		let each_type = 0;
-		let each_type;
 
 		if (
 			node.key &&
 			(node.key.type !== 'Identifier' || !node.index || node.key.name !== node.index)
 		) {
-			each_type = EACH_KEYED;
+			each_type |= EACH_KEYED;
 			if (
 				node.key.type === 'Identifier' &&
 				node.context.type === 'Identifier' &&
@@ -2141,12 +2141,17 @@ export const template_visitors = {
 				each_type |= EACH_INDEX_REACTIVE;
 			}
 		} else {
-			each_type = EACH_ITEM_REACTIVE;
+			each_type |= EACH_ITEM_REACTIVE;
 		}
+
 		if (each_node_meta.is_controlled) {
 			each_type |= EACH_IS_CONTROLLED;
 		}
 
+		if (context.state.analysis.immutable) {
+			each_type |= EACH_IS_IMMUTABLE;
+		}
+
 		// Find the parent each blocks which contain the arrays to invalidate
 		// TODO decide how much of this we want to keep for runes mode. For now we're bailing out below
 		const indirect_dependencies = collect_parent_each_blocks(context).flatMap((block) => {

packages/svelte/src/constants.js

@@ -4,6 +4,7 @@ export const EACH_KEYED = 1 << 2;
 export const EACH_IS_CONTROLLED = 1 << 3;
 export const EACH_IS_ANIMATED = 1 << 4;
 export const EACH_IS_PROXIED = 1 << 5;
+export const EACH_IS_IMMUTABLE = 1 << 6;
 
 /** List of Element events that will be delegated */
 export const DelegatedEvents = [

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

@@ -2,6 +2,7 @@ import {
 	EACH_INDEX_REACTIVE,
 	EACH_IS_ANIMATED,
 	EACH_IS_CONTROLLED,
+	EACH_IS_IMMUTABLE,
 	EACH_IS_PROXIED,
 	EACH_ITEM_REACTIVE,
 	EACH_KEYED
@@ -21,6 +22,7 @@ import {
 	destroy_signal,
 	execute_effect,
 	lazy_property,
+	mutable_source,
 	push_destroy_fn,
 	render_effect,
 	schedule_task,
@@ -747,6 +749,8 @@ function each_item_block(array, item, key, index, render_fn, flags) {
 			? lazy_property(array, index)
 			: each_item_not_reactive
 			? item
+			: (flags & EACH_IS_IMMUTABLE) === 0
+			? mutable_source(item)
 			: source(item);
 	const index_value = (flags & EACH_INDEX_REACTIVE) === 0 ? index : source(index);
 	const block = create_each_item_block(item_value, index_value, key);

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

@@ -44,7 +44,8 @@ import {
 	current_component_context,
 	pop,
 	unwrap,
-	default_equals
+	default_equals,
+	mutable_source
 } from './runtime.js';
 import {
 	current_hydration_fragment,
@@ -2625,7 +2626,6 @@ export function createRoot(component, options) {
 	 */
 	function add_prop(name, value) {
 		const prop = source(value);
-		prop.e = default_equals; // TODO should this be safe_equals?
 		_sources[name] = prop;
 		define_property(_props, name, {
 			get() {
@@ -2659,10 +2659,9 @@ export function createRoot(component, options) {
 			return _props[property];
 		}
 	});
-	const props_source = source(props_proxy);
 
 	// We're resetting the same proxy instance for updates, therefore bypass equality checks
-	props_source.e = safe_equal;
+	const props_source = mutable_source(props_proxy);
 
 	let [accessors, $destroy] = mount(component, {
 		...options,

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

@@ -163,7 +163,7 @@ function create_source_signal(flags, value) {
 			// consumers
 			c: null,
 			// equals
-			e: null,
+			e: default_equals,
 			// flags
 			f: flags,
 			// value
@@ -178,7 +178,7 @@ function create_source_signal(flags, value) {
 		// consumers
 		c: null,
 		// equals
-		e: null,
+		e: default_equals,
 		// flags
 		f: flags,
 		// value
@@ -698,7 +698,7 @@ export function store_get(store, store_name, stores) {
 		entry = {
 			store: null,
 			last_value: null,
-			value: source(UNINITIALIZED),
+			value: mutable_source(UNINITIALIZED),
 			unsubscribe: EMPTY_FUNC
 		};
 		// TODO: can we remove this code? it was refactored out when we split up source/comptued signals
@@ -1148,10 +1148,21 @@ export function derived(init) {
 export function source(initial_value) {
 	const source = create_source_signal(SOURCE | CLEAN, initial_value);
 	source.x = current_component_context;
-	source.e = get_equals_method();
 	return source;
 }
 
+/**
+ * @template V
+ * @param {V} initial_value
+ * @returns {import('./types.js').SourceSignal<V>}
+ */
+/*#__NO_SIDE_EFFECTS__*/
+export function mutable_source(initial_value) {
+	const s = source(initial_value);
+	s.e = safe_equal;
+	return s;
+}
+
 /**
  * @returns {import('./types.js').EqualsFunctions}
  */
@@ -1424,11 +1435,12 @@ export function is_store(val) {
  * @template V
  * @param {import('./types.js').MaybeSignal<Record<string, unknown>>} props_obj
  * @param {string} key
+ * @param {boolean} immutable
  * @param {V | (() => V)} [default_value]
  * @param {boolean} [call_default_value]
  * @returns {import('./types.js').Signal<V> | (() => V)}
  */
-export function prop_source(props_obj, key, default_value, call_default_value) {
+export function prop_source(props_obj, key, immutable, default_value, call_default_value) {
 	const props = is_signal(props_obj) ? get(props_obj) : props_obj;
 	const possible_signal = /** @type {import('./types.js').MaybeSignal<V>} */ (
 		expose(() => props[key])
@@ -1440,8 +1452,7 @@ export function prop_source(props_obj, key, default_value, call_default_value) {
 	if (
 		is_signal(possible_signal) &&
 		possible_signal.v === value &&
-		update_bound_prop === undefined &&
+		update_bound_prop === undefined
-		get_equals_method() === possible_signal.e
 	) {
 		if (should_set_default_value) {
 			set(
@@ -1459,13 +1470,11 @@ export function prop_source(props_obj, key, default_value, call_default_value) {
 			call_default_value ? default_value() : default_value;
 	}
 
-	const source_signal = source(value);
+	const source_signal = immutable ? source(value) : mutable_source(value);
 
 	// Synchronize prop changes with source signal.
 	// Needs special equality checking because the prop in the
 	// parent could be changed through `foo.bar = 'new value'`.
-	const immutable = /** @type {import('./types.js').ComponentContext} */ (current_component_context)
-		.i;
 	let ignore_next1 = false;
 	let ignore_next2 = false;
 	let did_update_to_defined = !should_set_default_value;

packages/svelte/src/internal/index.js

@@ -7,6 +7,7 @@ export {
 	expose,
 	exposable,
 	source,
+	mutable_source,
 	derived,
 	prop,
 	prop_source,

packages/svelte/tests/runtime-legacy/samples/binding-input-checkbox-deep-contextual/main.svelte

@@ -11,4 +11,4 @@
 	<div><input type='checkbox' bind:checked={item.completed}><p>{item.description}</p></div>
 {/each}
 
-<p>{numCompleted} completed</p>
+<p>{numCompleted} completed</p>

packages/svelte/tests/snapshot/samples/svelte-element/_expected/client/index.svelte.js

@@ -6,7 +6,7 @@ import * as $ from "svelte/internal";
 export default function Svelte_element($$anchor, $$props) {
 	$.push($$props, true);
 
-	let tag = $.prop_source($$props, "tag", 'hr', false);
+	let tag = $.prop_source($$props, "tag", true, 'hr', false);
 	/* Init */
 	var fragment = $.comment($$anchor);
 	var node = $.child_frag(fragment);
@@ -14,4 +14,4 @@ export default function Svelte_element($$anchor, $$props) {
 	$.element(node, () => $.get(tag));
 	$.close_frag($$anchor, fragment);
 	$.pop();
-}
+}