From 3e7589360a94eca01c547b7e9cb34006b53e7f88 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Fri, 24 Oct 2025 13:17:52 -0400
Subject: [PATCH] WIP

---
 .../src/compiler/phases/2-analyze/index.js    | 23 +++++++++++++++-
 .../svelte/src/compiler/phases/types.d.ts     | 27 ++++++++++++++++++-
 2 files changed, 48 insertions(+), 2 deletions(-)

diff --git a/packages/svelte/src/compiler/phases/2-analyze/index.js b/packages/svelte/src/compiler/phases/2-analyze/index.js
index b4c704c34d..5c653c7f2e 100644
--- a/packages/svelte/src/compiler/phases/2-analyze/index.js
+++ b/packages/svelte/src/compiler/phases/2-analyze/index.js
@@ -543,7 +543,9 @@ export function analyze_component(root, source, options) {
 		snippet_renderers: new Map(),
 		snippets: new Set(),
 		async_deriveds: new Set(),
-		pickled_awaits: new Set()
+		pickled_awaits: new Set(),
+		awaited_declarations: new Map(),
+		awaited_statements: new Map()
 	};
 
 	if (!runes) {
@@ -687,6 +689,25 @@ export function analyze_component(root, source, options) {
 			e.legacy_rest_props_invalid(rest_props_refs[0].node);
 		}
 
+		if (instance.has_await) {
+			let awaiting = false;
+			let i = 0;
+
+			for (const node of instance.ast.body) {
+				const has_await = has_await_expression(node);
+				awaiting ||= has_await;
+
+				if (!awaiting) continue;
+
+				const id = b.id(`$$${i++}`);
+
+				analysis.awaited_statements.set(node, {
+					id,
+					has_await
+				});
+			}
+		}
+
 		for (const { ast, scope, scopes } of [module, instance, template]) {
 			/** @type {AnalysisState} */
 			const state = {
diff --git a/packages/svelte/src/compiler/phases/types.d.ts b/packages/svelte/src/compiler/phases/types.d.ts
index 4e287fd199..79fa4ab88e 100644
--- a/packages/svelte/src/compiler/phases/types.d.ts
+++ b/packages/svelte/src/compiler/phases/types.d.ts
@@ -5,7 +5,10 @@ import type {
 	ClassBody,
 	Identifier,
 	LabeledStatement,
-	Program
+	ModuleDeclaration,
+	Pattern,
+	Program,
+	Statement
 } from 'estree';
 import type { Scope, ScopeRoot } from './scope.js';
 
@@ -108,6 +111,28 @@ export interface ComponentAnalysis extends Analysis {
 	 * Every snippet that is declared locally
 	 */
 	snippets: Set<AST.SnippetBlock>;
+	/**
+	 * A lookup of awaited declarations. If you have something this in `<script>`...
+	 *
+	 *   let a = await get_a();
+	 *   let b = get_b();
+	 *
+	 * ...it will get transformed to something like this...
+	 *
+	 *   let $$0 = $.run([], () => get_a());
+	 *   let $$1 = $.run([$$0], () => get_b());
+	 *
+	 * ...and references to `a` or `b` in the template should be mediated by `$$0` and `$$1`
+	 */
+	awaited_declarations: Map<
+		string,
+		{ id: Identifier; pattern: Pattern; updated_by: Set<Identifier> }
+	>;
+	/**
+	 * Information about top-level instance statements that need to be transformed
+	 * so that we can run the template synchronously
+	 */
+	awaited_statements: Map<Statement | ModuleDeclaration, { id: Identifier; has_await: boolean }>;
 }
 
 declare module 'estree' {