use comments to never run into the sole-element case

Author: dummdidumm

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

@@ -270,6 +270,19 @@ export function clean_nodes(
 
 	var 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
+	// and would still call node.replaceWith() on the script tag, it would be a no-op because the script tag has no parent.
+	if (trimmed.length === 1 && first.type === 'RegularElement' && first.name === 'script') {
+		trimmed.push({
+			type: 'Comment',
+			data: '',
+			parent: first.parent,
+			start: -1,
+			end: -1
+		});
+	}
+
 	return {
 		hoisted,
 		trimmed,

packages/svelte/src/internal/client/dom/template.js

@@ -185,13 +185,7 @@ function run_scripts(node) {
 			effect.nodes_end = clone;
 		}
 
-		// If node === script tag, replaceWith will do nothing because there's no parent yet
-		if (script === node) {
-			// but we can returns the cloned <script> immediately
-			return clone;
-		} else {
-			script.replaceWith(clone);
-		}
+		script.replaceWith(clone);
 	}
 	return node;
 }