Return a promise instead of undefined from empty async functions

async-to-promises.ts

@@ -3443,8 +3443,9 @@ export default function({ types, template, traverse, transformFromAst, version }
 						const canThrow = checkForErrorsAndRewriteReturns(bodyPath, this, inlineHelpers);
 						const parentPath = path.parentPath;
 						const skipReturn = parentPath.isCallExpression() && parentPath.node.callee === path.node && parentPath.parentPath.isExpressionStatement();
-						if (inlineHelpers && !pathsReturnOrThrowCurrentNodes(bodyPath).all && !skipReturn) {
-							path.node.body.body.push(types.returnStatement(types.callExpression(promiseResolve(), [])));
+						if (!skipReturn && !pathsReturnOrThrowCurrentNodes(bodyPath).all) {
+							const awaitHelper = inlineHelpers ? promiseResolve() : helperReference(this, path, "_await");
+							path.node.body.body.push(types.returnStatement(types.callExpression(awaitHelper, [])));
 						}
 						if (skipReturn) {
 							path.traverse(unwrapReturnPromiseVisitor);

tests/default argument pattern/output.js

@@ -1 +1 @@
-const f=_async((_arg)=>{if(_arg===undefined)_arg=(x++,{});let{y=(z++,{})}=_arg;});let x=0,z=0;
+const f=_async((_arg)=>{if(_arg===undefined)_arg=(x++,{});let{y=(z++,{})}=_arg;return _await();});let x=0,z=0;

tests/empty function with unused declaration/case-result.js

@@ -0,0 +1,5 @@
+async f => {
+	const result = f();
+	expect(result.constructor).toBe(Promise);
+	expect((await result)).toBe(undefined);
+}

tests/empty function with unused declaration/hoisted.js

@@ -0,0 +1 @@
+function(){const unused=1;return _await();}

tests/empty function with unused declaration/inlined.js

@@ -0,0 +1 @@
+function(){const unused=1;return Promise.resolve();}

tests/empty function with unused declaration/input.js

@@ -0,0 +1,3 @@
+async function() {
+	const unused = 1;
+}

tests/empty function with unused declaration/output.js

@@ -0,0 +1 @@
+()=>{const unused=1;return _await();}

tests/empty function/case-result.js

@@ -0,0 +1,5 @@
+async f => {
+	const result = f();
+	expect(result.constructor).toBe(Promise);
+	expect((await result)).toBe(undefined);
+}

tests/empty function/hoisted.js

@@ -0,0 +1 @@
+function(){return _await();}

tests/empty function/inlined.js

@@ -0,0 +1 @@
+function(){return Promise.resolve();}

tests/empty function/input.js

@@ -0,0 +1,2 @@
+async function() {
+}

tests/empty function/output.js

@@ -0,0 +1 @@
+()=>_await()