tidy up

packages/svelte/tests/types/snippet.ts

@@ -1,25 +1,40 @@
 import type { Snippet } from 'svelte';
 
+const return_type: ReturnType<Snippet> = null as any;
+
 // @ts-expect-error
 const a: Snippet<{ text: string }> = () => {};
 // @ts-expect-error
-const b: Snippet<boolean> = (a, b) => {};
+const b: Snippet<boolean> = (a, b) => {
+	return return_type;
+};
+// @ts-expect-error
+const c: Snippet<boolean> = (a: string) => {
+	return return_type;
+};
 // @ts-expect-error
-const c: Snippet<boolean> = (a: string) => {};
+const d: Snippet<boolean> = (a: string, b: number) => {
+	return return_type;
+};
 // @ts-expect-error
-const d: Snippet<boolean> = (a: string, b: number) => {};
+const e: Snippet = (a: string) => {
+	return return_type;
+};
 // @ts-expect-error
-const e: Snippet = (a: string) => {};
 const f: Snippet = (a) => {
-	// @ts-expect-error
 	a?.x;
+	return return_type;
 };
-const g: Snippet<[boolean]> = (internals, a) => {
+const g: Snippet<[boolean]> = (a) => {
 	// @ts-expect-error
-	a() === '';
-	a() === true;
+	a === '';
+	a === true;
+	return return_type;
+};
+const h: Snippet<[{ a: true }]> = (a) => {
+	a.a === true;
+	return return_type;
 };
-const h: Snippet<[{ a: true }]> = (internals, a) => {
-	a().a === true;
+const i: Snippet = () => {
+	return return_type;
 };
-const i: Snippet = () => {};

packages/svelte/types/index.d.ts

@@ -261,10 +261,7 @@ declare module 'svelte' {
 		element?: typeof HTMLElement;
 	};
 
-	/**
-	 * Internal implementation details that vary between environments
-	 */
-	export type SnippetInternals = Branded<{}, 'SnippetInternals'>;
+	const SnippetReturn: unique symbol;
 
 	// Use an interface instead of a type, makes for better intellisense info because the type is named in more situations.
 	/**
@@ -281,12 +278,13 @@ declare module 'svelte' {
 	export interface Snippet<Parameters extends unknown[] = []> {
 		(
 			this: void,
-			internal: SnippetInternals,
 			// this conditional allows tuples but not arrays. Arrays would indicate a
 			// rest parameter type, which is not supported. If rest parameters are added
 			// in the future, the condition can be removed.
-			...args: number extends Parameters['length'] ? never : Getters<Parameters>
-		): void;
+			...args: number extends Parameters['length'] ? never : Parameters
+		): typeof SnippetReturn & {
+			_: 'functions passed to {@render ...} tags must use the `Snippet` type imported from "svelte"';
+		};
 	}
 
 	interface DispatchOptions {