feat: allow $state in return statements

.changeset/sharp-rings-march.md

@@ -0,0 +1,5 @@
+---
+'svelte': minor
+---
+
+feat: allow `$state` in return statements

packages/svelte/src/compiler/phases/2-analyze/visitors/CallExpression.js

@@ -112,6 +112,20 @@ export function CallExpression(node, context) {
 		}
 
 		case '$state':
+			if (
+				(!(parent.type === 'VariableDeclarator' || parent.type === 'ReturnStatement') ||
+					get_parent(context.path, -3).type === 'ConstTag') &&
+				!(parent.type === 'PropertyDefinition' && !parent.static && !parent.computed) &&
+				!(parent.type === 'ArrowFunctionExpression' && parent.body === node)
+			) {
+				e.state_invalid_placement(node, rune);
+			}
+
+			if (node.arguments.length > 1) {
+				e.rune_invalid_arguments_length(node, rune, 'zero or one arguments');
+			}
+
+			break;
 		case '$state.raw':
 		case '$derived':
 		case '$derived.by':

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

@@ -4,12 +4,14 @@ import { dev, is_ignored } from '../../../../state.js';
 import * as b from '../../../../utils/builders.js';
 import { get_rune } from '../../../scope.js';
 import { transform_inspect_rune } from '../../utils.js';
+import { should_proxy } from '../utils.js';
 
 /**
  * @param {CallExpression} node
  * @param {Context} context
  */
 export function CallExpression(node, context) {
+	const parent = context.path.at(-1);
 	switch (get_rune(node, context.state.scope)) {
 		case '$host':
 			return b.id('$$props.$$host');
@@ -33,6 +35,23 @@ export function CallExpression(node, context) {
 		case '$inspect':
 		case '$inspect().with':
 			return transform_inspect_rune(node, context);
+		case '$state':
+			if (
+				parent?.type === 'ReturnStatement' ||
+				(parent?.type === 'ArrowFunctionExpression' && parent.body === node)
+			) {
+				if (
+					node.arguments[0] &&
+					should_proxy(
+						/** @type {Expression} */ (context.visit(node.arguments[0])),
+						context.state.scope
+					)
+				) {
+					return b.call('$.proxy', node.arguments[0]);
+				} else {
+					return node.arguments[0] ?? b.void0;
+				}
+			}
 	}
 
 	if (

packages/svelte/src/compiler/phases/3-transform/server/visitors/CallExpression.js

@@ -1,4 +1,4 @@
-/** @import { CallExpression, Expression } from 'estree' */
+/** @import { ArrowFunctionExpression, CallExpression, Expression } from 'estree' */
 /** @import { Context } from '../types.js' */
 import { is_ignored } from '../../../../state.js';
 import * as b from '../../../../utils/builders.js';
@@ -37,5 +37,17 @@ export function CallExpression(node, context) {
 		return transform_inspect_rune(node, context);
 	}
 
+	if (
+		rune === '$state' &&
+		(context.path.at(-1)?.type === 'ReturnStatement' ||
+			(context.path.at(-1)?.type === 'ArrowFunctionExpression' &&
+				/** @type {ArrowFunctionExpression} */ (context.path.at(-1)).body === node))
+	) {
+		if (node.arguments[0]) {
+			return context.visit(node.arguments[0]);
+		}
+		return b.void0;
+	}
+
 	context.next();
 }

packages/svelte/tests/snapshot/samples/state-in-return/_expected/client/index.svelte.js

@@ -0,0 +1,14 @@
+/* index.svelte.js generated by Svelte VERSION */
+import * as $ from 'svelte/internal/client';
+
+export default function proxy(object) {
+	return $.proxy(object);
+}
+
+export function createCounter() {
+	let count = $.state(0);
+
+	$.update(count);
+}
+
+export const proxy_in_arrow = (object) => $.proxy(object);

packages/svelte/tests/snapshot/samples/state-in-return/_expected/server/index.svelte.js

@@ -0,0 +1,14 @@
+/* index.svelte.js generated by Svelte VERSION */
+import * as $ from 'svelte/internal/server';
+
+export default function proxy(object) {
+	return object;
+}
+
+export function createCounter() {
+	let count = 0;
+
+	count++;
+}
+
+export const proxy_in_arrow = (object) => object;

packages/svelte/tests/snapshot/samples/state-in-return/index.svelte.js

@@ -0,0 +1,8 @@
+export default function proxy(object) {
+	return $state(object);
+}
+export function createCounter() {
+	let count = $state(0);
+	count++;
+}
+export const proxy_in_arrow = (object) => $state(object);