add attachments symbol

packages/svelte/src/attachments/index.js

@@ -0,0 +1 @@
+export { ATTACHMENTS_SYMBOL as AttachmentsKey } from '../internal/client/constants.js';

packages/svelte/src/attachments/public.d.ts

@@ -0,0 +1,4 @@
+/**
+ * A unique symbol used for defining the attachments to be applied to an element or component.
+ */
+export const AttachmentsKey: unique symbol;

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

@@ -25,3 +25,4 @@ export const STATE_SYMBOL = Symbol('$state');
 export const STATE_SYMBOL_METADATA = Symbol('$state metadata');
 export const LEGACY_PROPS = Symbol('legacy props');
 export const LOADING_ATTR_SYMBOL = Symbol('');
+export const ATTACHMENTS_SYMBOL = Symbol.for('svelte.attachments');

packages/svelte/src/internal/client/dom/elements/attributes.js

@@ -4,7 +4,7 @@ import { get_descriptors, get_prototype_of } from '../../../shared/utils.js';
 import { create_event, delegate } from './events.js';
 import { add_form_reset_listener, autofocus } from './misc.js';
 import * as w from '../../warnings.js';
-import { LOADING_ATTR_SYMBOL } from '../../constants.js';
+import { ATTACHMENTS_SYMBOL, LOADING_ATTR_SYMBOL } from '../../constants.js';
 import { queue_idle_task } from '../task.js';
 import { is_capture_event, is_delegated, normalize_attribute } from '../../../../utils.js';
 import {
@@ -416,8 +416,11 @@ export function set_attributes(
 		}
 	}
 
-	for (let symbol of Object.getOwnPropertySymbols(next)) {
-		attach(element, () => next[symbol]);
+	const attachments = next[ATTACHMENTS_SYMBOL];
+	if (attachments) {
+		for (let attachment of attachments) {
+			attach(element, () => attachment);
+		}
 	}
 
 	return current;

packages/svelte/types/index.d.ts

@@ -593,6 +593,13 @@ declare module 'svelte/action' {
 	export {};
 }
 
+declare module 'svelte/attachments' {
+	/**
+	 * A unique symbol used for defining the attachments to be applied to an element or component.
+	 */
+	export const AttachmentsKey: unique symbol;
+}
+
 declare module 'svelte/animate' {
 	// todo: same as Transition, should it be shared?
 	export interface AnimationConfig {
@@ -1881,10 +1888,10 @@ declare module 'svelte/motion' {
 		 * 	const tween = Tween.of(() => number);
 		 * </script>
 		 * ```
-		 * 
+		 *
 		 */
 		static of<U>(fn: () => U, options?: TweenedOptions<U> | undefined): Tween<U>;
-		
+
 		constructor(value: T, options?: TweenedOptions<T>);
 		/**
 		 * Sets `tween.target` to `value` and returns a `Promise` that resolves if and when `tween.current` catches up to it.
@@ -1903,21 +1910,21 @@ declare module 'svelte/motion' {
 
 declare module 'svelte/reactivity' {
 	export class SvelteDate extends Date {
-		
+
 		constructor(...params: any[]);
 		#private;
 	}
 	export class SvelteSet<T> extends Set<T> {
-		
+
 		constructor(value?: Iterable<T> | null | undefined);
-		
+
 		add(value: T): this;
 		#private;
 	}
 	export class SvelteMap<K, V> extends Map<K, V> {
-		
+
 		constructor(value?: Iterable<readonly [K, V]> | null | undefined);
-		
+
 		set(key: K, value: V): this;
 		#private;
 	}
@@ -1927,7 +1934,7 @@ declare module 'svelte/reactivity' {
 	}
 	const REPLACE: unique symbol;
 	export class SvelteURLSearchParams extends URLSearchParams {
-		
+
 		[REPLACE](params: URLSearchParams): void;
 		#private;
 	}
@@ -1999,7 +2006,7 @@ declare module 'svelte/reactivity' {
 	 */
 	export function createSubscriber(start: (update: () => void) => (() => void) | void): () => void;
 	class ReactiveValue<T> {
-		
+
 		constructor(fn: () => T, onsubscribe: (update: () => void) => void);
 		get current(): T;
 		#private;
@@ -2064,7 +2071,7 @@ declare module 'svelte/reactivity/window' {
 		get current(): number | undefined;
 	};
 	class ReactiveValue<T> {
-		
+
 		constructor(fn: () => T, onsubscribe: (update: () => void) => void);
 		get current(): T;
 		#private;