From e3e101f2a871d9917c29ff7ab8c97dc727429f32 Mon Sep 17 00:00:00 2001
From: Dominic Gannaway <dg@domgan.com>
Date: Thu, 31 Oct 2024 18:32:10 +0000
Subject: [PATCH] fix: ensure transitions are applied to nested elements

---
 .changeset/modern-adults-lay.md               |  5 ++++
 .../src/compiler/phases/2-analyze/index.js    |  2 ++
 .../2-analyze/visitors/TransitionDirective.js | 14 +++++++++++
 .../transition-static-subtree/_config.js      | 23 +++++++++++++++++++
 .../transition-static-subtree/main.svelte     | 18 +++++++++++++++
 5 files changed, 62 insertions(+)
 create mode 100644 .changeset/modern-adults-lay.md
 create mode 100644 packages/svelte/src/compiler/phases/2-analyze/visitors/TransitionDirective.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/transition-static-subtree/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/transition-static-subtree/main.svelte

diff --git a/.changeset/modern-adults-lay.md b/.changeset/modern-adults-lay.md
new file mode 100644
index 0000000000..9caa3962af
--- /dev/null
+++ b/.changeset/modern-adults-lay.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: ensure transitions are applied to nested elements
diff --git a/packages/svelte/src/compiler/phases/2-analyze/index.js b/packages/svelte/src/compiler/phases/2-analyze/index.js
index 89c2e19c3f..f5a31d09a7 100644
--- a/packages/svelte/src/compiler/phases/2-analyze/index.js
+++ b/packages/svelte/src/compiler/phases/2-analyze/index.js
@@ -63,6 +63,7 @@ import { SvelteWindow } from './visitors/SvelteWindow.js';
 import { TaggedTemplateExpression } from './visitors/TaggedTemplateExpression.js';
 import { Text } from './visitors/Text.js';
 import { TitleElement } from './visitors/TitleElement.js';
+import { TransitionDirective } from './visitors/TransitionDirective.js';
 import { UpdateExpression } from './visitors/UpdateExpression.js';
 import { UseDirective } from './visitors/UseDirective.js';
 import { VariableDeclarator } from './visitors/VariableDeclarator.js';
@@ -172,6 +173,7 @@ const visitors = {
 	SvelteWindow,
 	TaggedTemplateExpression,
 	Text,
+	TransitionDirective,
 	TitleElement,
 	UpdateExpression,
 	UseDirective,
diff --git a/packages/svelte/src/compiler/phases/2-analyze/visitors/TransitionDirective.js b/packages/svelte/src/compiler/phases/2-analyze/visitors/TransitionDirective.js
new file mode 100644
index 0000000000..c218f741c3
--- /dev/null
+++ b/packages/svelte/src/compiler/phases/2-analyze/visitors/TransitionDirective.js
@@ -0,0 +1,14 @@
+/** @import { AST } from '#compiler' */
+/** @import { Context } from '../types' */
+
+import { mark_subtree_dynamic } from './shared/fragment.js';
+
+/**
+ * @param {AST.TransitionDirective} node
+ * @param {Context} context
+ */
+export function TransitionDirective(node, context) {
+	mark_subtree_dynamic(context.path);
+
+	context.next();
+}
diff --git a/packages/svelte/tests/runtime-runes/samples/transition-static-subtree/_config.js b/packages/svelte/tests/runtime-runes/samples/transition-static-subtree/_config.js
new file mode 100644
index 0000000000..99563ef959
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/transition-static-subtree/_config.js
@@ -0,0 +1,23 @@
+import { flushSync } from '../../../../src/index-client.js';
+import { test } from '../../test';
+
+export default test({
+	async test({ assert, raf, target }) {
+		assert.htmlEqual(target.innerHTML, '<button>Toggle</button><div><span>123</span></div>');
+
+		const btn1 = target.querySelector('button');
+		btn1?.click();
+		flushSync();
+		raf.tick(250);
+
+		assert.htmlEqual(
+			target.innerHTML,
+			'<button>Toggle</button><div><span style="opacity: 0.5;">123</span></div>'
+		);
+
+		flushSync();
+		raf.tick(500);
+
+		assert.htmlEqual(target.innerHTML, '<button>Toggle</button>');
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/transition-static-subtree/main.svelte b/packages/svelte/tests/runtime-runes/samples/transition-static-subtree/main.svelte
new file mode 100644
index 0000000000..4a15e15699
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/transition-static-subtree/main.svelte
@@ -0,0 +1,18 @@
+<script>
+	function fade(_) {
+		return {
+			duration: 500,
+			css: t => `opacity: ${t}`,
+		}
+	}
+
+	let visible = $state(true);
+</script>
+
+<button onclick={() => visible = !visible}>Toggle</button>
+
+{#if visible}
+	<div>
+		<span transition:fade>123</span>
+	</div>
+{/if}