fix: invoke `onchange` in component constructor

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

@@ -45,16 +45,6 @@ export function build_getter(node, state) {
 	return node;
 }
 
-/**
- * @param {Expression} value
- * @param {Expression} previous
- */
-export function build_proxy_reassignment(value, previous) {
-	return dev
-		? b.call('$.proxy', value, b.call('$.get_options', previous), b.null, previous)
-		: b.call('$.proxy', value, b.call('$.get_options', previous));
-}
-
 /**
  * @param {FunctionDeclaration | FunctionExpression | ArrowFunctionExpression} node
  * @param {ComponentContext} context

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

@@ -9,7 +9,7 @@ import {
 	is_event_attribute
 } from '../../../../utils/ast.js';
 import { dev, filename, is_ignored, locate_node, locator } from '../../../../state.js';
-import { build_proxy_reassignment, should_proxy } from '../utils.js';
+import { should_proxy } from '../utils.js';
 import { visit_assignment_expression } from '../../shared/assignments.js';
 
 /**
@@ -70,18 +70,16 @@ function build_assignment(operator, left, right, context) {
 				is_non_coercive_operator(operator) &&
 				should_proxy(value, context.state.scope);
 
-			if (context.state.in_constructor) {
-				// inside the constructor, we can assign to `this.#foo.v` rather than using `$.set`,
-				// since nothing is tracking the signal at this point
-				return b.assignment(
-					operator,
-					/** @type {Pattern} */ (context.visit(left)),
-					needs_proxy ? build_proxy_reassignment(value, b.member(b.this, private_state.id)) : value
+			return b.call(
+				// inside the constructor, we use `$.simple_set` rather than using `$.set`,
+				// that only assign the value and eventually call onchange since nothing is tracking the signal at this point
+				context.state.in_constructor ? '$.simple_set' : '$.set',
+				left,
+				value,
+				needs_proxy && b.true,
+				dev && needs_proxy && b.true
 			);
 		}
-
-			return b.call('$.set', left, value, needs_proxy && b.true, dev && needs_proxy && b.true);
-		}
 	}
 
 	let object = left;

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

@@ -109,7 +109,14 @@ export {
 	user_effect,
 	user_pre_effect
 } from './reactivity/effects.js';
-export { mutable_state, mutate, set, state, get_options } from './reactivity/sources.js';
+export {
+	mutable_state,
+	mutate,
+	set,
+	simple_set,
+	state,
+	get_options
+} from './reactivity/sources.js';
 export {
 	prop,
 	rest_props,

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

@@ -206,6 +206,26 @@ export function set(source, value, should_proxy = false, needs_previous = false)
 	return internal_set(source, new_value);
 }
 
+/**
+ * @template V
+ * @param {Source<V>} source
+ * @param {V} value
+ * @param {boolean} [should_proxy]
+ * @param {boolean} [needs_previous]
+ * @returns {V}
+ */
+export function simple_set(source, value, should_proxy = false, needs_previous = false) {
+	let new_value = should_proxy
+		? needs_previous
+			? proxy(value, source.o, null, source)
+			: proxy(value, source.o)
+		: value;
+
+	source.v = new_value;
+
+	return new_value;
+}
+
 /**
  * @template V
  * @param {Source<V>} source

packages/svelte/tests/runtime-runes/samples/state-onchange/_config.js

@@ -4,6 +4,11 @@ import { test } from '../../test';
 export default test({
 	async test({ assert, target, logs }) {
 		const [btn, btn2, btn3, btn4, btn5, btn6, btn7, btn8, btn9] = target.querySelectorAll('button');
+
+		assert.deepEqual(logs, ['constructor count', 'constructor proxy']);
+
+		logs.length = 0;
+
 		flushSync(() => {
 			btn.click();
 		});

packages/svelte/tests/runtime-runes/samples/state-onchange/main.svelte

@@ -22,6 +22,24 @@
 				console.log("class proxy");
 			}
 		})
+
+		#in_constructor = $state(0, {
+			onchange(){
+				console.log("constructor count");
+			}
+		});
+
+		#in_constructor_proxy = $state({ count: 0 }, {
+			onchange(){
+				console.log("constructor proxy");
+			}
+		});
+
+
+		constructor(){
+			this.#in_constructor++;
+			this.#in_constructor_proxy.count++;
+		}
 	}
 
 	const class_test = new Test();

packages/svelte/tests/runtime-runes/samples/state-raw-onchange/_config.js

@@ -5,6 +5,11 @@ export default test({
 	async test({ assert, target, logs }) {
 		const [btn, btn2, btn3, btn4, btn5, btn6, btn7, btn8, btn9, btn10] =
 			target.querySelectorAll('button');
+
+		assert.deepEqual(logs, ['constructor count', 'constructor proxy']);
+
+		logs.length = 0;
+
 		flushSync(() => {
 			btn.click();
 		});

packages/svelte/tests/runtime-runes/samples/state-raw-onchange/main.svelte

@@ -22,6 +22,24 @@
 				console.log("class proxy");
 			}
 		})
+
+		#in_constructor = $state(0, {
+			onchange(){
+				console.log("constructor count");
+			}
+		});
+
+		#in_constructor_proxy = $state({ count: 0 }, {
+			onchange(){
+				console.log("constructor proxy");
+			}
+		});
+
+
+		constructor(){
+			this.#in_constructor++;
+			this.#in_constructor_proxy.count++;
+		}
 	}
 
 	const class_test = new Test();

packages/svelte/tests/snapshot/samples/class-state-field-constructor-assignment/_expected/client/index.svelte.js

@@ -19,7 +19,7 @@ export default function Class_state_field_constructor_assignment($$anchor, $$pro
 
 		constructor() {
 			this.a = 1;
-			this.#b.v = 2;
+			$.simple_set(this.#b, 2);
 		}
 	}