gah i give up for now. need sleep

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

@@ -206,16 +206,93 @@ export function client_component(source, analysis, options) {
 		}
 	}
 
-	for (const [node] of analysis.reactive_statements) {
-		const statement = [...state.legacy_reactive_statements].find(([n]) => n === node);
-		if (statement === undefined) {
-			error(node, 'INTERNAL', 'Could not find reactive statement');
+	const legacy_reactive_statements = Array.from(analysis.reactive_statements.keys()).map(
+		(node) =>
+			/** @type {import('./types').LegacyReactiveStatement} */ (
+				state.legacy_reactive_statements.get(node)
+			)
+	);
+
+	/** @type {import('#compiler').Binding[]} */
+	const dependencies = [];
+
+	for (const statement of legacy_reactive_statements) {
+		if (statement.dependencies.length === 0) {
+			instance.body.push(statement.body);
+		} else {
+			for (const dep of statement.dependencies) {
+				if (!dependencies.includes(dep)) {
+					dependencies.push(dep);
+				}
+			}
 		}
-		instance.body.push(statement[1]);
 	}
 
-	if (analysis.reactive_statements.size > 0) {
-		instance.body.push(b.stmt(b.call('$.legacy_pre_effect_reset')));
+	if (dependencies.length > 0) {
+		instance.body.push(b.var('$$deps', b.array(dependencies.map((dep) => b.literal(-1)))));
+
+		/** @type {import('estree').Statement[]} */
+		const body = [
+			b.stmt(
+				b.sequence(
+					dependencies.map((binding) =>
+						binding.kind === 'bindable_prop' || binding.kind === 'rest_prop'
+							? b.call(
+									'$.deep_read_state',
+									serialize_get_binding(b.id(binding.node.name), instance_state)
+								)
+							: serialize_get_binding(b.id(binding.node.name), instance_state)
+					)
+				)
+			)
+		];
+
+		const versions = dependencies.map((binding) => {
+			if (
+				binding.kind === 'state' ||
+				binding.kind === 'frozen_state' ||
+				binding.kind === 'derived'
+			) {
+				return b.member(binding.node, b.id('version'));
+			}
+
+			return b.call(
+				'$.get_version',
+				b.thunk(serialize_get_binding(b.id(binding.node.name), instance_state))
+			);
+		});
+
+		for (const statement of legacy_reactive_statements) {
+			const { dependencies } = statement;
+			if (dependencies.length === 0) continue;
+
+			let condition = null;
+
+			for (const binding of dependencies) {
+				const index = dependencies.indexOf(binding);
+				const version = versions[index];
+
+				const comparison = b.binary(
+					'!==',
+					version,
+					b.member(b.id('$$deps'), b.literal(index), true)
+				);
+
+				condition = condition ? b.logical('||', condition, comparison) : comparison;
+			}
+
+			body.push(
+				b.if(/** @type {import('estree').Expression} */ (condition), b.block([statement.body]))
+			);
+		}
+
+		for (let i = 0; i < dependencies.length; i += 1) {
+			body.push(
+				b.stmt(b.assignment('=', b.member(b.id('$$deps'), b.literal(i), true), versions[i]))
+			);
+		}
+
+		instance.body.push(b.stmt(b.call('$.render_effect', b.thunk(b.block(body)))));
 	}
 
 	/**

packages/svelte/src/compiler/phases/3-transform/client/types.d.ts

@@ -5,10 +5,15 @@ import type {
 	Identifier,
 	PrivateIdentifier
 } from 'estree';
-import type { Namespace, SvelteNode, ValidatedCompileOptions } from '#compiler';
+import type { Binding, Namespace, SvelteNode, ValidatedCompileOptions } from '#compiler';
 import type { TransformState } from '../types.js';
 import type { ComponentAnalysis } from '../../types.js';
 
+export interface LegacyReactiveStatement {
+	dependencies: Binding[];
+	body: Statement;
+}
+
 export interface ClientTransformState extends TransformState {
 	readonly private_state: Map<string, StateField>;
 	readonly public_state: Map<string, StateField>;
@@ -20,7 +25,7 @@ export interface ClientTransformState extends TransformState {
 	readonly in_constructor: boolean;
 
 	/** The $: calls, which will be ordered in the end */
-	readonly legacy_reactive_statements: Map<LabeledStatement, Statement>;
+	readonly legacy_reactive_statements: Map<LabeledStatement, LegacyReactiveStatement>;
 }
 
 export interface ComponentClientTransformState extends ClientTransformState {

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

@@ -148,44 +148,19 @@ export const javascript_visitors_legacy = {
 
 		if (!reactive_stmt) return; // not the instance context
 
-		const { dependencies } = reactive_stmt;
-
-		let serialized_body = /** @type {import('estree').Statement} */ (context.visit(node.body));
-
-		if (serialized_body.type !== 'BlockStatement') {
-			serialized_body = b.block([serialized_body]);
-		}
-
-		const body = serialized_body.body;
-
-		/** @type {import('estree').Expression[]} */
-		const sequence = [];
-		for (const binding of dependencies) {
-			if (binding.kind === 'normal') continue;
-
-			const name = binding.node.name;
-			let serialized = serialize_get_binding(b.id(name), state);
-
-			// If the binding is a prop, we need to deep read it because it could be fine-grained $state
-			// from a runes-component, where mutations don't trigger an update on the prop as a whole.
-			if (name === '$$props' || name === '$$restProps' || binding.kind === 'bindable_prop') {
-				serialized = b.call('$.deep_read_state', serialized);
+		/** @type {import('#compiler').Binding[]} */
+		const dependencies = [];
+		for (const dependency of reactive_stmt.dependencies) {
+			if (dependency.kind !== 'normal') {
+				dependencies.push(dependency);
 			}
-
-			sequence.push(serialized);
 		}
 
 		// these statements will be topologically ordered later
-		state.legacy_reactive_statements.set(
-			node,
-			b.stmt(
-				b.call(
-					'$.legacy_pre_effect',
-					sequence.length > 0 ? b.thunk(b.sequence(sequence)) : b.thunk(b.block([])),
-					b.thunk(b.block(body))
-				)
-			)
-		);
+		state.legacy_reactive_statements.set(node, {
+			dependencies,
+			body: /** @type {import('estree').Statement} */ (context.visit(node.body))
+		});
 
 		return b.empty;
 	},

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

@@ -135,7 +135,7 @@ var uses_version_sum = false;
 export function get_version(fn) {
 	version_sum = 0;
 	uses_version_sum = true;
-	fn();
+	deep_read_state(untrack(fn));
 	return version_sum;
 }
 
@@ -1177,6 +1177,7 @@ export function deep_read(value, visited = new Set()) {
 			proto !== Date.prototype
 		) {
 			const descriptors = get_descriptors(proto);
+
 			for (let key in descriptors) {
 				const get = descriptors[key].get;
 				if (get) {

packages/svelte/src/internal/index.js

@@ -1,6 +1,6 @@
 export {
 	get,
-	get_version_sum,
+	get_version,
 	invalidate_inner_signals,
 	flushSync,
 	tick,