fix: correctly migrate named self closing slots (#17199)

Author: paoloricciuti

.changeset/fuzzy-fans-hammer.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: correctly migrate named self closing slots

packages/svelte/src/compiler/migrate/index.js

@@ -1058,17 +1058,19 @@ const template = {
 		handle_identifier(node, state, path);
 	},
 	RegularElement(node, { state, path, next }) {
-		migrate_slot_usage(node, path, state);
-		handle_events(node, state);
 		// Strip off any namespace from the beginning of the node name.
 		const node_name = node.name.replace(/[a-zA-Z-]*:/g, '');
 
 		if (state.analysis.source[node.end - 2] === '/' && !is_void(node_name) && !is_svg(node_name)) {
 			let trimmed_position = node.end - 2;
 			while (state.str.original.charAt(trimmed_position - 1) === ' ') trimmed_position--;
 			state.str.remove(trimmed_position, node.end - 1);
-			state.str.appendRight(node.end, `</${node.name}>`);
+			state.str.appendLeft(node.end, `</${node.name}>`);
 		}
+
+		migrate_slot_usage(node, path, state);
+		handle_events(node, state);
+
 		next();
 	},
 	SvelteSelf(node, { state, next }) {

packages/svelte/tests/migrate/samples/self-closing-named-slot/input.svelte

@@ -0,0 +1,3 @@
+<Component>
+	<div slot="test" />
+</Component>

packages/svelte/tests/migrate/samples/self-closing-named-slot/output.svelte

@@ -0,0 +1,5 @@
+<Component>
+	{#snippet test()}
+		<div ></div>
+	{/snippet}
+</Component>