WIP

packages/svelte/src/internal/client/dev/hmr.js

@@ -71,7 +71,7 @@ export function hmr(original, get_source) {
 		// The `get_source` parameter reads `wrapper[HMR].source`, but in the `accept`
 		// function we always replace it with `previous[HMR].source`, which in practice
 		// means we only ever update the original
-		source: source(original)
+		source: source(original, null)
 	};
 
 	return wrapper;

packages/svelte/src/internal/client/dom/blocks/await.js

@@ -53,8 +53,8 @@ export function await_block(node, get_input, pending_fn, then_fn, catch_fn) {
 	var catch_effect;
 
 	var input_source = runes
-		? source(/** @type {V} */ (undefined))
-		: mutable_source(/** @type {V} */ (undefined));
+		? source(/** @type {V} */ (undefined), null)
+		: mutable_source(/** @type {V} */ (undefined), null);
 	var error_source = runes ? source(undefined) : mutable_source(undefined);
 	var resolved = false;
 

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

@@ -469,8 +469,8 @@ function create_item(anchor, state, prev, next, value, key, index, render_fn, fl
 		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 i = (flags & EACH_INDEX_REACTIVE) === 0 ? index : source(index);
+		var v = reactive ? (mutable ? mutable_source(value) : source(value, null)) : value;
+		var i = (flags & EACH_INDEX_REACTIVE) === 0 ? index : source(index, null);
 
 		/** @type {EachItem} */
 		var item = {

packages/svelte/src/internal/client/dom/legacy/misc.js

@@ -8,7 +8,7 @@ import { is_array } from '../../../shared/utils.js';
  * @param {() => any} fn
  */
 export function reactive_import(fn) {
-	var s = source(0);
+	var s = source(0, null);
 
 	return function () {
 		if (arguments.length === 1) {

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

@@ -105,7 +105,7 @@ export {
 	user_effect,
 	user_pre_effect
 } from './reactivity/effects.js';
-export { mutable_source, mutate, source, set } from './reactivity/sources.js';
+export { mutable_source, mutate, source, set, state } from './reactivity/sources.js';
 export {
 	prop,
 	rest_props,

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

@@ -80,7 +80,7 @@ export function proxy(value, parent = null, prev) {
 			var s = sources.get(prop);
 
 			if (s === undefined) {
-				s = source(descriptor.value);
+				s = source(descriptor.value, null);
 				sources.set(prop, s);
 			} else {
 				set(s, proxy(descriptor.value, metadata));
@@ -193,7 +193,7 @@ export function proxy(value, parent = null, prev) {
 			// object property before writing to that property.
 			if (s === undefined) {
 				if (!has || get_descriptor(target, prop)?.writable) {
-					s = source(undefined);
+					s = source(undefined, null);
 					set(s, proxy(value, metadata));
 					sources.set(prop, s);
 				}

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

@@ -150,7 +150,10 @@ const legacy_rest_props_handler = {
  * @returns {Record<string, unknown>}
  */
 export function legacy_rest_props(props, exclude) {
-	return new Proxy({ props, exclude, special: {}, version: source(0) }, legacy_rest_props_handler);
+	return new Proxy(
+		{ props, exclude, special: {}, version: source(0, null) },
+		legacy_rest_props_handler
+	);
 }
 
 /**

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

@@ -58,6 +58,15 @@ export function source(v, owner = current_reaction) {
 	return source;
 }
 
+/**
+ * @template V
+ * @param {V} v
+ * @returns {Source<V>}
+ */
+export function state(v) {
+	return source(v);
+}
+
 /**
  * @template V
  * @param {V} initial_value
@@ -65,10 +74,18 @@ export function source(v, owner = current_reaction) {
  * @returns {Source<V>}
  */
 /*#__NO_SIDE_EFFECTS__*/
-export function mutable_source(initial_value, owner) {
+export function mutable_source(initial_value, owner = current_reaction) {
 	const s = source(initial_value, owner);
 	s.equals = safe_equals;
 
+	if (owner !== null && (owner.f & DERIVED) !== 0) {
+		if (derived_sources === null) {
+			set_derived_sources([s]);
+		} else {
+			derived_sources.push(s);
+		}
+	}
+
 	// bind the signal to the component context, in case we need to
 	// track updates to trigger beforeUpdate/afterUpdate callbacks
 	if (current_component_context !== null && current_component_context.l !== null) {

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

@@ -1001,7 +1001,7 @@ export function push(props, runes = false, fn) {
 			s: null,
 			u: null,
 			r1: [],
-			r2: source(false)
+			r2: source(false, null)
 		};
 	}
 

packages/svelte/src/reactivity/date.js

@@ -6,7 +6,7 @@ import { get } from '../internal/client/runtime.js';
 var inited = false;
 
 export class SvelteDate extends Date {
-	#time = source(super.getTime());
+	#time = source(super.getTime(), null);
 
 	/** @type {Map<keyof Date, Source<unknown>>} */
 	#deriveds = new Map();

packages/svelte/src/reactivity/map.js

@@ -12,8 +12,8 @@ import { increment } from './utils.js';
 export class SvelteMap extends Map {
 	/** @type {Map<K, Source<number>>} */
 	#sources = new Map();
-	#version = source(0);
-	#size = source(0);
+	#version = source(0, null);
+	#size = source(0, null);
 
 	/**
 	 * @param {Iterable<readonly [K, V]> | null | undefined} [value]
@@ -40,7 +40,7 @@ export class SvelteMap extends Map {
 		if (s === undefined) {
 			var ret = super.get(key);
 			if (ret !== undefined) {
-				s = source(0);
+				s = source(0, null);
 				sources.set(key, s);
 			} else {
 				// We should always track the version in case
@@ -71,7 +71,7 @@ export class SvelteMap extends Map {
 		if (s === undefined) {
 			var ret = super.get(key);
 			if (ret !== undefined) {
-				s = source(0);
+				s = source(0, null);
 				sources.set(key, s);
 			} else {
 				// We should always track the version in case
@@ -96,7 +96,7 @@ export class SvelteMap extends Map {
 		var res = super.set(key, value);
 
 		if (s === undefined) {
-			sources.set(key, source(0));
+			sources.set(key, source(0, null));
 			set(this.#size, super.size);
 			increment(this.#version);
 		} else if (prev_res !== value) {
@@ -144,7 +144,7 @@ export class SvelteMap extends Map {
 		if (this.#size.v !== sources.size) {
 			for (var key of super.keys()) {
 				if (!sources.has(key)) {
-					sources.set(key, source(0));
+					sources.set(key, source(0, null));
 				}
 			}
 		}

packages/svelte/src/reactivity/url-search-params.js

@@ -6,7 +6,7 @@ import { increment } from './utils.js';
 export const REPLACE = Symbol();
 
 export class SvelteURLSearchParams extends URLSearchParams {
-	#version = source(0);
+	#version = source(0, null);
 	#url = get_current_url();
 
 	#updating = false;

packages/svelte/src/reactivity/url.js

@@ -11,14 +11,14 @@ export function get_current_url() {
 }
 
 export class SvelteURL extends URL {
-	#protocol = source(super.protocol);
-	#username = source(super.username);
-	#password = source(super.password);
-	#hostname = source(super.hostname);
-	#port = source(super.port);
-	#pathname = source(super.pathname);
-	#hash = source(super.hash);
-	#search = source(super.search);
+	#protocol = source(super.protocol, null);
+	#username = source(super.username, null);
+	#password = source(super.password, null);
+	#hostname = source(super.hostname, null);
+	#port = source(super.port, null);
+	#pathname = source(super.pathname, null);
+	#hash = source(super.hash, null);
+	#search = source(super.search, null);
 	#searchParams;
 
 	/**

packages/svelte/src/store/index-client.js

@@ -106,7 +106,7 @@ export function toStore(get, set) {
  */
 export function fromStore(store) {
 	let value = /** @type {V} */ (undefined);
-	let version = source(0);
+	let version = source(0, null);
 	let subscribers = 0;
 
 	let unsubscribe = noop;