fix: improve whitespace handling (#9912)

revert

Author: trueadm

.changeset/dull-mangos-wave.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: improve whitespace handling

packages/svelte/src/compiler/phases/3-transform/utils.js

@@ -177,8 +177,9 @@ export function clean_nodes(
 			node.data = node.data.replace(regex_whitespaces_strict, ' ');
 			node.raw = node.raw.replace(regex_whitespaces_strict, ' ');
 			if (
-				(last_text === null || !regex_ends_with_whitespaces.test(last_text.data)) &&
-				(!can_remove_entirely || node.data !== ' ')
+				(last_text === null && !can_remove_entirely) ||
+				node.data !== ' ' ||
+				node.data.charCodeAt(0) === 160 // non-breaking space
 			) {
 				trimmed.push(node);
 			}

packages/svelte/tests/runtime-runes/samples/snippet-whitespace/_config.js

@@ -0,0 +1,8 @@
+import { test } from '../../test';
+
+export default test({
+	compileOptions: {
+		dev: true // Render in dev mode to check that the validation error is not thrown
+	},
+	html: `A\nB\nC\nD`
+});

packages/svelte/tests/runtime-runes/samples/snippet-whitespace/main.svelte

@@ -0,0 +1,5 @@
+A
+{#snippet snip()}C{/snippet}
+B
+{@render snip()}
+D