fix: ensure `$$slots` returns a record of booleans

Returned the underlying functions previously

.changeset/shaggy-comics-jog.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: ensure `$$slots` returns a record of booleans

packages/svelte/src/internal/client/dom/blocks/slot.js

@@ -13,3 +13,17 @@ export function slot(anchor, slot_fn, slot_props, fallback_fn) {
 		slot_fn(anchor, slot_props);
 	}
 }
+
+/**
+ * @param {Record<string, any>} props
+ * @returns {Record<string, boolean>}
+ */
+export function sanitize_slots(props) {
+	/** @type {Record<string, boolean>} */
+	const sanitized = {};
+	if (props.children) sanitized.default = true;
+	for (const key in props.$$slots) {
+		sanitized[key] = true;
+	}
+	return sanitized;
+}

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

@@ -15,7 +15,7 @@ export { key_block as key } from './dom/blocks/key.js';
 export { css_props } from './dom/blocks/css-props.js';
 export { index, each } from './dom/blocks/each.js';
 export { html } from './dom/blocks/html.js';
-export { slot } from './dom/blocks/slot.js';
+export { sanitize_slots, slot } from './dom/blocks/slot.js';
 export { snippet, wrap_snippet } from './dom/blocks/snippet.js';
 export { component } from './dom/blocks/svelte-component.js';
 export { element } from './dom/blocks/svelte-element.js';
@@ -119,7 +119,7 @@ export {
 	update_pre_store,
 	update_store
 } from './reactivity/store.js';
-export { append_styles, sanitize_slots, set_text } from './render.js';
+export { append_styles, set_text } from './render.js';
 export {
 	get,
 	invalidate_inner_signals,

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

@@ -267,16 +267,6 @@ export function unmount(component) {
 	fn?.();
 }
 
-/**
- * @param {Record<string, any>} props
- * @returns {Record<string, any>}
- */
-export function sanitize_slots(props) {
-	const sanitized = { ...props.$$slots };
-	if (props.children) sanitized.default = props.children;
-	return sanitized;
-}
-
 /**
  * @param {Node} target
  * @param {string} style_sheet_id

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

@@ -446,11 +446,15 @@ export function sanitize_props(props) {
 
 /**
  * @param {Record<string, any>} props
- * @returns {Record<string, any>}
+ * @returns {Record<string, boolean>}
  */
 export function sanitize_slots(props) {
-	const sanitized = { ...props.$$slots };
-	if (props.children) sanitized.default = props.children;
+	/** @type {Record<string, boolean>} */
+	const sanitized = {};
+	if (props.children) sanitized.default = true;
+	for (const key in props.$$slots) {
+		sanitized[key] = true;
+	}
 	return sanitized;
 }
 

packages/svelte/tests/runtime-legacy/samples/slot/A.svelte

@@ -1,21 +1,20 @@
 <script>
-  let data = '';
+	let data = '';
 
-  if ($$slots.b) {
-    data = 'foo';
-  }
+	if ($$slots.b) {
+		data = 'foo';
+	}
 
-  export function getData() {
-    return data;
-  }
+	export function getData() {
+		return data;
+	}
 
-  function toString(data) {
-    const result = {};
-    const sortedKeys = Object.keys(data).sort();
-    // TODO added !! to make it work since $$slots exposes the slot functions - we need to decide what to do with them
-    sortedKeys.forEach((key) => (result[key] = !!data[key]));
-    return JSON.stringify(result);
-  }
+	function toString(data) {
+		const result = {};
+		const sortedKeys = Object.keys(data).sort();
+		sortedKeys.forEach((key) => (result[key] = data[key]));
+		return JSON.stringify(result);
+	}
 </script>
 
 <slot />
@@ -24,9 +23,9 @@
 $$slots: {toString($$slots)}
 
 {#if $$slots.b}
-  <div>
-    <slot name="b" />
-  </div>
+	<div>
+		<slot name="b" />
+	</div>
 {:else}
-  Slot b is not available
+	Slot b is not available
 {/if}