fix: skip certain slot validations for custom elements (#10207)

fixes #10196

.changeset/blue-timers-film.md

@@ -0,0 +1,5 @@
+---
+"svelte": patch
+---
+
+fix: skip certain slot validations for custom elements

packages/svelte/src/compiler/phases/2-analyze/validation.js

@@ -172,16 +172,21 @@ function validate_slot_attribute(context, attribute) {
 			error(attribute, 'invalid-slot-attribute');
 		}
 
-		if (owner.type === 'Component' || owner.type === 'SvelteComponent') {
+		if (
+			owner.type === 'Component' ||
+			owner.type === 'SvelteComponent' ||
+			owner.type === 'SvelteSelf'
+		) {
 			if (owner !== context.path.at(-2)) {
 				error(attribute, 'invalid-slot-placement');
 			}
-		}
 
 			const name = attribute.value[0].data;
+
 			if (context.state.component_slots.has(name)) {
 				error(attribute, 'duplicate-slot-name', name, owner.name);
 			}
+
 			context.state.component_slots.add(name);
 
 			if (name === 'default') {
@@ -199,6 +204,7 @@ function validate_slot_attribute(context, attribute) {
 					error(node, 'invalid-default-slot-content');
 				}
 			}
+		}
 	} else {
 		error(attribute, 'invalid-slot-placement');
 	}

packages/svelte/tests/compiler-errors/samples/component-slot-duplicate-error/main.svelte

@@ -2,6 +2,12 @@
 	import Nested from './irrelevant';
 </script>
 
+<!-- allowed in custom elements -->
+<c-e>
+    <c-e-item slot="allowed"></c-e-item>
+    <c-e-item slot="allowed"></c-e-item>
+</c-e>
+
 <Nested>
 	<p slot="foo">{value}</p>
 	<p slot="foo">{value}</p>