add missing runtime requirement for async module header

active async modules when top level await is used

lib/WebpackOptionsApply.js

@@ -308,10 +308,18 @@ class WebpackOptionsApply extends OptionsApply {
 
 		new RuntimePlugin().apply(compiler);
 
-		if (options.experiments.importAwait || options.experiments.importAsync) {
+		if (
+			options.experiments.importAwait ||
+			options.experiments.importAsync ||
+			options.experiments.topLevelAwait
+		) {
 			const InferAsyncModulesPlugin = require("./async-modules/InferAsyncModulesPlugin");
 			new InferAsyncModulesPlugin({
-				errorOnMissingAwait: !options.experiments.importAsync
+				errorOnImport: options.experiments.importAsync
+					? false
+					: options.experiments.importAwait
+					? "await"
+					: true
 			}).apply(compiler);
 		}
 

lib/async-modules/InferAsyncModulesPlugin.js

@@ -13,9 +13,12 @@ const HarmonyImportSideEffectDependency = require("../dependencies/HarmonyImport
 /** @typedef {import("../Module")} Module */
 
 class InferAsyncModulesPlugin {
-	constructor(options) {
-		const { errorOnMissingAwait = false } = options || {};
-		this.errorOnMissingAwait = errorOnMissingAwait;
+	/**
+	 * @param {Object} options options object
+	 * @param {boolean | "await"=} options.errorOnImport false: no error, true: error when importing async module, "await": error when import async module without import await
+	 */
+	constructor({ errorOnImport = false } = {}) {
+		this.errorOnImport = errorOnImport;
 	}
 	/**
 	 * @param {Compiler} compiler webpack compiler
@@ -41,12 +44,14 @@ class InferAsyncModulesPlugin {
 							const dep = connection.dependency;
 							if (dep instanceof HarmonyImportDependency && connection.active) {
 								if (
-									this.errorOnMissingAwait &&
+									this.errorOnImport &&
 									dep instanceof HarmonyImportSideEffectDependency &&
-									!dep.await
+									(this.errorOnImport === true || !dep.await)
 								) {
 									const error = new WebpackError(
-										"Tried to import async module with normal import/export (must use 'import await'/'export await' instead)"
+										this.errorOnImport === true
+											? "Tried to import async module with import/export (must enable experiments.importAsync to allow this)"
+											: "Tried to import async module with normal import/export (must use 'import await'/'export await' instead)"
 									);
 									error.module = module;
 									error.loc = dep.loc;

lib/dependencies/HarmonyCompatibilityDependency.js

@@ -56,13 +56,17 @@ HarmonyCompatibilityDependency.Template = class HarmonyExportDependencyTemplate
 		}
 		if (moduleGraph.isAsync(module)) {
 			runtimeRequirements.add(RuntimeGlobals.module);
+			if (usedExports !== false)
+				runtimeRequirements.add(RuntimeGlobals.exports);
 			initFragments.push(
 				new InitFragment(
 					`${module.moduleArgument}.exports = (async () => {\n`,
 					InitFragment.STAGE_ASYNC_BOUNDARY,
 					0,
 					undefined,
-					`\nreturn ${module.exportsArgument};\n})();`
+					usedExports !== false
+						? `\nreturn ${module.exportsArgument};\n})();`
+						: "\n})();"
 				)
 			);
 		}

test/cases/async-modules/top-level-await-without-export/index.js

@@ -0,0 +1,14 @@
+let value = 0;
+
+it("should not crash when top level await is used without export", () => {
+	// wait for itself
+	return require.cache[module.id].exports.then(() => {
+		expect(value).toBe(42);
+	});
+});
+
+await new Promise(r => setTimeout(r, 100));
+
+value = 42;
+
+export {};