chore: simplify `<pre>` cleaning (#15980)

.changeset/fifty-llamas-know.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+chore: simplify `<pre>` cleaning

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

@@ -271,21 +271,14 @@ export function clean_nodes(
 
 	var first = trimmed[0];
 
-	// initial newline inside a `<pre>` is disregarded, if not followed by another newline
+	// if first text node inside a <pre> is a single newline, discard it, because otherwise
+	// the browser will do it for us which could break hydration
 	if (parent.type === 'RegularElement' && parent.name === 'pre' && first?.type === 'Text') {
-		const text = first.data.replace(regex_starts_with_newline, '');
-		if (text !== first.data) {
-			const tmp = text.replace(regex_starts_with_newline, '');
-			if (text === tmp) {
-				first.data = text;
-				first.raw = first.raw.replace(regex_starts_with_newline, '');
-				if (first.data === '') {
+		if (first.data === '\n' || first.data === '\r\n') {
 			trimmed.shift();
 			first = trimmed[0];
 		}
 	}
-		}
-	}
 
 	// Special case: Add a comment if this is a lone script tag. This ensures that our run_scripts logic in template.js
 	// will always be able to call node.replaceWith() on the script tag in order to make it run. If we don't add this