update type

packages/svelte/elements.d.ts

@@ -31,6 +31,8 @@
 // Definitions: https://github.com/DefinitelyTyped/DefinitelyTyped
 // TypeScript Version: 2.8
 
+import { AttachmentsKey } from 'svelte/attachments';
+
 // Note: We also allow `null` as a valid value because Svelte treats this the same as `undefined`
 
 type Booleanish = boolean | 'true' | 'false';
@@ -861,7 +863,7 @@ export interface HTMLAttributes<T extends EventTarget> extends AriaAttributes, D
 	[key: `data-${string}`]: any;
 
 	// allow any attachment
-	[key: symbol]: (node: T) => void | (() => void);
+	[AttachmentsKey]: Array<(node: T) => void | (() => void)>;
 }
 
 export type HTMLAttributeAnchorTarget = '_self' | '_blank' | '_parent' | '_top' | (string & {});

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

@@ -1,4 +1,9 @@
+declare const brand: unique symbol;
+type Brand<B> = { [brand]: B };
+type Branded<T, B> = T & Brand<B>;
+type AttachmentsKeySymbol = Branded<symbol, 'svelte.attachments'>;
+
 /**
  * A unique symbol used for defining the attachments to be applied to an element or component.
  */
-export const AttachmentsKey: unique symbol;
+export const AttachmentsKey: AttachmentsKeySymbol;

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

@@ -267,7 +267,7 @@ export function build_component(node, component_name, context, anchor = context.
 				push_prop(
 					b.prop(
 						'get',
-						b.call('Symbol'),
+						b.call("Symbol.for('svelte.attachments')"),
 						/** @type {Expression} */ (
 							context.visit(attachment.type === 'SpreadElement' ? attachment.argument : attachment)
 						),