perf: use Set for exclude checks in rest_props/exclude_from_object/legacy_rest_props

Replaces Array.includes() (O(n)) with Set.has() (O(1)) across three
sibling paths that were missed when client runes rest_props was updated:
- server/index.js:rest_props (called per SSR request)
- shared/utils.js:exclude_from_object (called for rest destructuring)
- client/reactivity/props.js:legacy_rest_props_handler ($$restProps proxy)

No signature changes — arrays are still accepted and converted to Set
internally. legacy_rest_props.deleteProperty push() → add() to match.

Fixes #18601

.changeset/fix-rest-props-set-membership.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+perf: use Set for exclude-list membership checks in rest_props, exclude_from_object, and legacy_rest_props

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

@@ -96,11 +96,11 @@ export function rest_props(props, exclude, name) {
 
 /**
  * The proxy handler for legacy $$restProps and $$props
- * @type {ProxyHandler<{ props: Record<string | symbol, unknown>, exclude: Array<string | symbol>, special: Record<string | symbol, (v?: unknown) => unknown>, version: Source<number>, parent_effect: Effect }>}}
+ * @type {ProxyHandler<{ props: Record<string | symbol, unknown>, exclude: Set<string | symbol>, special: Record<string | symbol, (v?: unknown) => unknown>, version: Source<number>, parent_effect: Effect }>}}
  */
 const legacy_rest_props_handler = {
 	get(target, key) {
-		if (target.exclude.includes(key)) return;
+		if (target.exclude.has(key)) return;
 		get(target.version);
 		return key in target.special ? target.special[key]() : target.props[key];
 	},
@@ -132,7 +132,7 @@ const legacy_rest_props_handler = {
 		return true;
 	},
 	getOwnPropertyDescriptor(target, key) {
-		if (target.exclude.includes(key)) return;
+		if (target.exclude.has(key)) return;
 		if (key in target.props) {
 			return {
 				enumerable: true,
@@ -143,17 +143,17 @@ const legacy_rest_props_handler = {
 	},
 	deleteProperty(target, key) {
 		// Svelte 4 allowed for deletions on $$restProps
-		if (target.exclude.includes(key)) return true;
-		target.exclude.push(key);
+		if (target.exclude.has(key)) return true;
+		target.exclude.add(key);
 		update(target.version);
 		return true;
 	},
 	has(target, key) {
-		if (target.exclude.includes(key)) return false;
+		if (target.exclude.has(key)) return false;
 		return key in target.props;
 	},
 	ownKeys(target) {
-		return Reflect.ownKeys(target.props).filter((key) => !target.exclude.includes(key));
+		return Reflect.ownKeys(target.props).filter((key) => !target.exclude.has(key));
 	}
 };
 
@@ -166,7 +166,7 @@ export function legacy_rest_props(props, exclude) {
 	return new Proxy(
 		{
 			props,
-			exclude,
+			exclude: new Set(exclude),
 			special: {},
 			version: source(0),
 			// TODO this is only necessary because we need to track component

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

@@ -347,11 +347,11 @@ export function slot(renderer, $$props, name, slot_props, fallback_fn) {
  * @returns {Record<string, unknown>}
  */
 export function rest_props(props, rest) {
+	const exclude = new Set(rest);
 	/** @type {Record<string, unknown>} */
 	const rest_props = {};
-	let key;
-	for (key of Object.keys(props)) {
-		if (!rest.includes(key)) {
+	for (const key of Object.keys(props)) {
+		if (!exclude.has(key)) {
 			rest_props[key] = props[key];
 		}
 	}

packages/svelte/src/internal/shared/utils.js

@@ -125,17 +125,18 @@ export function to_array(value, n) {
  * @returns {Record<string | symbol, unknown>}
  */
 export function exclude_from_object(obj, keys) {
+	const exclude = new Set(keys);
 	/** @type {Record<string | symbol, unknown>} */
 	var result = {};
 
 	for (var key in obj) {
-		if (!keys.includes(key)) {
+		if (!exclude.has(key)) {
 			result[key] = obj[key];
 		}
 	}
 
 	for (var symbol of Object.getOwnPropertySymbols(obj)) {
-		if (Object.propertyIsEnumerable.call(obj, symbol) && !keys.includes(symbol)) {
+		if (Object.propertyIsEnumerable.call(obj, symbol) && !exclude.has(symbol)) {
 			result[symbol] = obj[symbol];
 		}
 	}