From b7510b016d8d9a391cce7245299ef338499fb91d Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Sat, 25 Oct 2025 21:49:57 -0400
Subject: [PATCH] WIP

---
 .../3-transform/server/visitors/IfBlock.js    | 16 +++++++---
 .../server/visitors/shared/utils.js           | 10 +++++--
 .../svelte/src/internal/server/renderer.js    | 29 +++++++++++++++++--
 .../async-if-after-await-in-script/_config.js | 16 ++++++++++
 .../main.svelte                               | 10 +++++++
 5 files changed, 71 insertions(+), 10 deletions(-)
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-if-after-await-in-script/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-if-after-await-in-script/main.svelte

diff --git a/packages/svelte/src/compiler/phases/3-transform/server/visitors/IfBlock.js b/packages/svelte/src/compiler/phases/3-transform/server/visitors/IfBlock.js
index a869a8edf1..ca614a93e2 100644
--- a/packages/svelte/src/compiler/phases/3-transform/server/visitors/IfBlock.js
+++ b/packages/svelte/src/compiler/phases/3-transform/server/visitors/IfBlock.js
@@ -23,12 +23,20 @@ export function IfBlock(node, context) {
 	/** @type {Statement} */
 	let statement = b.if(test, consequent, alternate);
 
-	if (
+	const is_async = node.metadata.expression.is_async();
+
+	const has_await =
 		node.metadata.expression.has_await ||
+		// TODO get rid of this stuff
 		node.consequent.metadata.has_await ||
-		node.alternate?.metadata.has_await
-	) {
-		statement = create_async_block(b.block([statement]));
+		node.alternate?.metadata.has_await;
+
+	if (is_async || has_await) {
+		statement = create_async_block(
+			b.block([statement]),
+			node.metadata.expression.blockers(),
+			!!has_await
+		);
 	}
 
 	context.state.template.push(statement, block_close);
diff --git a/packages/svelte/src/compiler/phases/3-transform/server/visitors/shared/utils.js b/packages/svelte/src/compiler/phases/3-transform/server/visitors/shared/utils.js
index 09a854670c..1e4ac69608 100644
--- a/packages/svelte/src/compiler/phases/3-transform/server/visitors/shared/utils.js
+++ b/packages/svelte/src/compiler/phases/3-transform/server/visitors/shared/utils.js
@@ -1,4 +1,4 @@
-/** @import { Expression, Identifier, Node, Statement, BlockStatement } from 'estree' */
+/** @import { Expression, Identifier, Node, Statement, BlockStatement, ArrayExpression } from 'estree' */
 /** @import { AST } from '#compiler' */
 /** @import { ComponentContext, ServerTransformState } from '../../types.js' */
 
@@ -275,9 +275,13 @@ export function create_child_block(body, async) {
 /**
  * Creates a `$$renderer.async(...)` expression statement
  * @param {BlockStatement | Expression} body
+ * @param {ArrayExpression} blockers
+ * @param {boolean} has_await
  */
-export function create_async_block(body) {
-	return b.stmt(b.call('$$renderer.async', b.arrow([b.id('$$renderer')], body, true)));
+export function create_async_block(body, blockers, has_await) {
+	return b.stmt(
+		b.call('$$renderer.async', blockers, b.arrow([b.id('$$renderer')], body, has_await))
+	);
 }
 
 /**
diff --git a/packages/svelte/src/internal/server/renderer.js b/packages/svelte/src/internal/server/renderer.js
index fb1af6ffbb..d20792c91f 100644
--- a/packages/svelte/src/internal/server/renderer.js
+++ b/packages/svelte/src/internal/server/renderer.js
@@ -100,18 +100,41 @@ export class Renderer {
 	}
 
 	/**
+	 * @param {Array<Promise<void>>} blockers
 	 * @param {(renderer: Renderer) => void} fn
 	 */
-	async(fn) {
+	async(blockers, fn) {
 		this.#out.push(BLOCK_OPEN);
-		this.child(fn);
+		this.child(
+			blockers.length > 0 ? (renderer) => Promise.all(blockers).then(() => fn(renderer)) : fn
+		);
 		this.#out.push(BLOCK_CLOSE);
 	}
 
 	/**
 	 * @param {Array<() => void>} thunks
 	 */
-	run(thunks) {}
+	run(thunks) {
+		const context = ssr_context;
+
+		let promise = Promise.resolve(thunks[0]());
+		const promises = [promise];
+
+		for (const fn of thunks.slice(1)) {
+			promise = promise.then(() => {
+				const previous_ssr_context = ssr_context;
+				set_ssr_context(context);
+
+				try {
+					return fn();
+				} finally {
+					set_ssr_context(previous_ssr_context);
+				}
+			});
+		}
+
+		return promises;
+	}
 
 	/**
 	 * Create a child renderer. The child renderer inherits the state from the parent,
diff --git a/packages/svelte/tests/runtime-runes/samples/async-if-after-await-in-script/_config.js b/packages/svelte/tests/runtime-runes/samples/async-if-after-await-in-script/_config.js
new file mode 100644
index 0000000000..2b8ab6e894
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-if-after-await-in-script/_config.js
@@ -0,0 +1,16 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	skip_mode: ['server'],
+
+	ssrHtml: '<p>yep</p>',
+
+	async test({ assert, target, variant }) {
+		if (variant === 'dom') {
+			await tick();
+		}
+
+		assert.htmlEqual(target.innerHTML, '<p>yep</p>');
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-if-after-await-in-script/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-if-after-await-in-script/main.svelte
new file mode 100644
index 0000000000..66dc7c718c
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-if-after-await-in-script/main.svelte
@@ -0,0 +1,10 @@
+<script>
+	await 0;
+	const condition = await true;
+</script>
+
+{#if condition}
+	<p>yep</p>
+{:else}
+	<p>nope</p>
+{/if}