fix: better await block scope analysis (#10849)

The await block scope analysis was flawed because it did not set the scope for the value/error field before visiting those nodes, resulting in the wrong scopes getting references
As a byproduct, this fixes #8141

Author: dummdidumm

packages/svelte/src/compiler/phases/scope.js

@@ -599,26 +599,38 @@ export function create_scopes(ast, root, allow_reactive_declarations, parent) {
 		},
 
 		AwaitBlock(node, context) {
-			context.next();
+			context.visit(node.expression);
+
+			if (node.pending) {
+				context.visit(node.pending);
+			}
 
-			if (node.then && node.value !== null) {
-				const then_scope = /** @type {Scope} */ (scopes.get(node.then));
-				const value_scope = context.state.scope.child();
-				for (const id of extract_identifiers(node.value)) {
-					then_scope.declare(id, 'normal', 'const');
-					value_scope.declare(id, 'normal', 'const');
+			if (node.then) {
+				context.visit(node.then);
+				if (node.value) {
+					const then_scope = /** @type {Scope} */ (scopes.get(node.then));
+					const value_scope = context.state.scope.child();
+					scopes.set(node.value, value_scope);
+					context.visit(node.value, { scope: value_scope });
+					for (const id of extract_identifiers(node.value)) {
+						then_scope.declare(id, 'normal', 'const');
+						value_scope.declare(id, 'normal', 'const');
+					}
 				}
-				scopes.set(node.value, value_scope);
 			}
 
-			if (node.catch && node.error !== null) {
-				const catch_scope = /** @type {Scope} */ (scopes.get(node.catch));
-				const error_scope = context.state.scope.child();
-				for (const id of extract_identifiers(node.error)) {
-					catch_scope.declare(id, 'normal', 'const');
-					error_scope.declare(id, 'normal', 'const');
+			if (node.catch) {
+				context.visit(node.catch);
+				if (node.error) {
+					const catch_scope = /** @type {Scope} */ (scopes.get(node.catch));
+					const error_scope = context.state.scope.child();
+					scopes.set(node.error, error_scope);
+					context.visit(node.error, { scope: error_scope });
+					for (const id of extract_identifiers(node.error)) {
+						catch_scope.declare(id, 'normal', 'const');
+						error_scope.declare(id, 'normal', 'const');
+					}
 				}
-				scopes.set(node.error, error_scope);
 			}
 		},
 

packages/svelte/tests/runtime-legacy/samples/binding-select-late-4/_config.js

@@ -0,0 +1,12 @@
+import { test } from '../../test';
+
+export default test({
+	async test({ assert, target }) {
+		await new Promise((r) => setTimeout(r, 200)); // wait for await block to resolve
+
+		const options = target.querySelectorAll('option');
+		assert.ok(!options[0].selected);
+		assert.ok(options[1].selected);
+		assert.ok(!options[2].selected);
+	}
+});

packages/svelte/tests/runtime-legacy/samples/binding-select-late-4/main.svelte

@@ -0,0 +1,19 @@
+<script>
+	let promise = getNumbers();
+	let selected = 2;
+
+	async function getNumbers() {
+		await new Promise(resolve => setTimeout(resolve, 100));
+		return [1, 2, 3];
+	}
+</script>
+
+<select bind:value={selected}>
+	{#await promise}
+		<option>-1</option>
+	{:then numbers}
+		{#each numbers as number}
+			<option>{number}</option>
+		{/each}
+	{/await}
+</select>