add experimental option

Author: Rich-Harris

packages/svelte/src/compiler/phases/2-analyze/index.js

@@ -263,7 +263,9 @@ export function analyze_module(ast, options) {
 			scope,
 			scopes,
 			// @ts-expect-error TODO
-			analysis
+			analysis,
+			// @ts-expect-error TODO
+			options
 		},
 		visitors
 	);

packages/svelte/src/compiler/phases/2-analyze/visitors/AwaitExpression.js

@@ -32,8 +32,14 @@ export function AwaitExpression(node, context) {
 		}
 	}
 
-	if (suspend && !context.state.analysis.runes) {
-		e.legacy_await_invalid(node);
+	if (suspend) {
+		if (!context.state.options.experimental.async) {
+			e.experimental_async(node);
+		}
+
+		if (!context.state.analysis.runes) {
+			e.legacy_await_invalid(node);
+		}
 	}
 
 	if (preserve_context) {

packages/svelte/tests/helpers.js

@@ -86,7 +86,8 @@ export async function compile_directory(
 				const compiled = compileModule(text, {
 					filename: opts.filename,
 					generate: opts.generate,
-					dev: opts.dev
+					dev: opts.dev,
+					experimental: opts.experimental
 				});
 				write(out, compiled.js.code.replace(`v${VERSION}`, 'VERSION'));
 			} else {

packages/svelte/tests/runtime-legacy/shared.ts

@@ -157,6 +157,9 @@ async function common_setup(cwd: string, runes: boolean | undefined, config: Run
 		rootDir: cwd,
 		dev: force_hmr ? true : undefined,
 		hmr: force_hmr ? true : undefined,
+		experimental: {
+			async: true
+		},
 		...config.compileOptions,
 		immutable: config.immutable,
 		accessors: 'accessors' in config ? config.accessors : true,