fix: allow child element with slot attribute within svelte:element (#9038)

fix #9018

Author: hackape

.changeset/nine-houses-flow.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: allow child element with slot attribute within svelte:element

packages/svelte/src/compiler/compile/nodes/Element.js

@@ -1413,7 +1413,9 @@ const regex_minus_sign = /-/;
 function within_custom_element(parent) {
 	while (parent) {
 		if (parent.type === 'InlineComponent') return false;
-		if (parent.type === 'Element' && regex_minus_sign.test(parent.name)) return true;
+		if (parent.type === 'Element') {
+			if (regex_minus_sign.test(parent.name) || parent.is_dynamic_element) return true;
+		}
 		parent = parent.parent;
 	}
 	return false;

packages/svelte/test/runtime/samples/slot-in-dynamic-element/_config.js

@@ -0,0 +1,7 @@
+export default {
+	html: `
+		<dynamic-element>
+			<header slot='header'>header header header</header>
+		</dynamic-element>
+	`
+};

packages/svelte/test/runtime/samples/slot-in-dynamic-element/main.svelte

@@ -0,0 +1,7 @@
+<script>
+	export let tagName = 'dynamic-element'
+</script>
+
+<svelte:element this={tagName}>
+	<header slot='header'>header header header</header>
+</svelte:element>