[fix] Removal of empty stylesheets created from transitions

src/runtime/internal/dom.ts

@@ -154,14 +154,9 @@ export function get_root_for_style(node: Node): ShadowRoot | Document {
 	return node.ownerDocument;
 }
 
-export function append_empty_stylesheet(node: Node) {
-	const style_element = element('style') as HTMLStyleElement;
-	append_stylesheet(get_root_for_style(node), style_element);
-	return style_element.sheet as CSSStyleSheet;
-}
-
-function append_stylesheet(node: ShadowRoot | Document, style: HTMLStyleElement) {
+export function append_stylesheet(node: ShadowRoot | Document, style: HTMLStyleElement) {
 	append((node as Document).head || node, style);
+	return style.sheet as CSSStyleSheet;
 }
 
 export function append_hydration(target: NodeEx, node: NodeEx) {

src/runtime/internal/style_manager.ts

@@ -1,8 +1,8 @@
-import { append_empty_stylesheet, get_root_for_style } from './dom';
+import { append_stylesheet, detach, element, get_root_for_style } from './dom';
 import { raf } from './environment';
 
 interface StyleInformation {
-	stylesheet: CSSStyleSheet;
+	style_element: HTMLStyleElement;
 	rules: Record<string, true>;
 }
 
@@ -20,8 +20,8 @@ function hash(str: string) {
 	return hash >>> 0;
 }
 
-function create_style_information(doc: Document | ShadowRoot, node: Element & ElementCSSInlineStyle) {
-	const info = { stylesheet: append_empty_stylesheet(node), rules: {} };
+function create_style_information(doc: Document | ShadowRoot) {
+	const info = { style_element: element('style'), rules: {} };
 	managed_styles.set(doc, info);
 	return info;
 }
@@ -39,9 +39,10 @@ export function create_rule(node: Element & ElementCSSInlineStyle, a: number, b:
 	const name = `__svelte_${hash(rule)}_${uid}`;
 	const doc = get_root_for_style(node);
 
-	const { stylesheet, rules } = managed_styles.get(doc) || create_style_information(doc, node);
+	const { style_element, rules } = managed_styles.get(doc) || create_style_information(doc);
 
 	if (!rules[name]) {
+		const stylesheet = append_stylesheet(doc, style_element);
 		rules[name] = true;
 		stylesheet.insertRule(`@keyframes ${name} ${rule}`, stylesheet.cssRules.length);
 	}
@@ -71,10 +72,8 @@ export function clear_rules() {
 	raf(() => {
 		if (active) return;
 		managed_styles.forEach(info => {
-			const { stylesheet } = info;
-			let i = stylesheet.cssRules.length;
-			while (i--) stylesheet.deleteRule(i);
-			info.rules = {};
+			const { style_element } = info;
+			detach(style_element);
 		});
 		managed_styles.clear();
 	});

test/runtime/samples/style_manager-cleanup/_config.js

@@ -0,0 +1,14 @@
+export default {
+	skip_if_ssr: true,
+	skip_if_hydrate: true,
+	skip_if_hydrate_from_ssr: true,
+	test({ raf, assert, component, window }) {
+		component.visible = true;
+		raf.tick(100);
+		component.visible = false;
+		raf.tick(200);
+		raf.tick(0);
+
+		assert.htmlEqual(window.document.head.innerHTML, '');
+	}
+};

test/runtime/samples/style_manager-cleanup/main.svelte

@@ -0,0 +1,14 @@
+<script>
+    export let visible = false;
+
+    function foo() {
+        return {
+            duration: 100,
+            css: () => ''
+        };
+    }
+    </script>
+
+    {#if visible}
+        <div transition:foo></div>
+    {/if}