From 62840175887f74bd2d2bb0d019bb35b6dcf7fa08 Mon Sep 17 00:00:00 2001
From: Ryan Petrich <rpetrich@gmail.com>
Date: Sat, 20 Jul 2019 12:42:57 -0400
Subject: [PATCH] Return a promise instead of undefined from empty async
 functions

---
 async-to-promises.ts                                        | 5 +++--
 tests/default argument pattern/hoisted.js                   | 2 +-
 tests/default argument pattern/output.js                    | 2 +-
 tests/empty function with unused declaration/case-result.js | 5 +++++
 tests/empty function with unused declaration/hoisted.js     | 1 +
 tests/empty function with unused declaration/inlined.js     | 1 +
 tests/empty function with unused declaration/input.js       | 3 +++
 tests/empty function with unused declaration/output.js      | 1 +
 tests/empty function/case-result.js                         | 5 +++++
 tests/empty function/hoisted.js                             | 1 +
 tests/empty function/inlined.js                             | 1 +
 tests/empty function/input.js                               | 2 ++
 tests/empty function/output.js                              | 1 +
 13 files changed, 26 insertions(+), 4 deletions(-)
 create mode 100644 tests/empty function with unused declaration/case-result.js
 create mode 100644 tests/empty function with unused declaration/hoisted.js
 create mode 100644 tests/empty function with unused declaration/inlined.js
 create mode 100644 tests/empty function with unused declaration/input.js
 create mode 100644 tests/empty function with unused declaration/output.js
 create mode 100644 tests/empty function/case-result.js
 create mode 100644 tests/empty function/hoisted.js
 create mode 100644 tests/empty function/inlined.js
 create mode 100644 tests/empty function/input.js
 create mode 100644 tests/empty function/output.js

diff --git a/async-to-promises.ts b/async-to-promises.ts
index 807ee9f..0d6838a 100644
--- a/async-to-promises.ts
+++ b/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);
diff --git a/tests/default argument pattern/hoisted.js b/tests/default argument pattern/hoisted.js
index af672c8..4241cac 100644
--- a/tests/default argument pattern/hoisted.js	
+++ b/tests/default argument pattern/hoisted.js	
@@ -1 +1 @@
-const f=_async(function(_arg){if(_arg===undefined)_arg=(x++,{});let{y=(z++,{})}=_arg;});let x=0,z=0;
\ No newline at end of file
+const f=_async(function(_arg){if(_arg===undefined)_arg=(x++,{});let{y=(z++,{})}=_arg;return _await();});let x=0,z=0;
\ No newline at end of file
diff --git a/tests/default argument pattern/output.js b/tests/default argument pattern/output.js
index 5624155..aabe6ec 100644
--- a/tests/default argument pattern/output.js	
+++ b/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;
\ No newline at end of file
+const f=_async((_arg)=>{if(_arg===undefined)_arg=(x++,{});let{y=(z++,{})}=_arg;return _await();});let x=0,z=0;
\ No newline at end of file
diff --git a/tests/empty function with unused declaration/case-result.js b/tests/empty function with unused declaration/case-result.js
new file mode 100644
index 0000000..508c12d
--- /dev/null
+++ b/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);
+}
\ No newline at end of file
diff --git a/tests/empty function with unused declaration/hoisted.js b/tests/empty function with unused declaration/hoisted.js
new file mode 100644
index 0000000..f3343ac
--- /dev/null
+++ b/tests/empty function with unused declaration/hoisted.js	
@@ -0,0 +1 @@
+function(){const unused=1;return _await();}
\ No newline at end of file
diff --git a/tests/empty function with unused declaration/inlined.js b/tests/empty function with unused declaration/inlined.js
new file mode 100644
index 0000000..9bfd1ca
--- /dev/null
+++ b/tests/empty function with unused declaration/inlined.js	
@@ -0,0 +1 @@
+function(){const unused=1;return Promise.resolve();}
\ No newline at end of file
diff --git a/tests/empty function with unused declaration/input.js b/tests/empty function with unused declaration/input.js
new file mode 100644
index 0000000..d1f7106
--- /dev/null
+++ b/tests/empty function with unused declaration/input.js	
@@ -0,0 +1,3 @@
+async function() {
+	const unused = 1;
+}
diff --git a/tests/empty function with unused declaration/output.js b/tests/empty function with unused declaration/output.js
new file mode 100644
index 0000000..7c07b9f
--- /dev/null
+++ b/tests/empty function with unused declaration/output.js	
@@ -0,0 +1 @@
+()=>{const unused=1;return _await();}
\ No newline at end of file
diff --git a/tests/empty function/case-result.js b/tests/empty function/case-result.js
new file mode 100644
index 0000000..508c12d
--- /dev/null
+++ b/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);
+}
\ No newline at end of file
diff --git a/tests/empty function/hoisted.js b/tests/empty function/hoisted.js
new file mode 100644
index 0000000..0bec6c8
--- /dev/null
+++ b/tests/empty function/hoisted.js	
@@ -0,0 +1 @@
+function(){return _await();}
\ No newline at end of file
diff --git a/tests/empty function/inlined.js b/tests/empty function/inlined.js
new file mode 100644
index 0000000..566bf61
--- /dev/null
+++ b/tests/empty function/inlined.js	
@@ -0,0 +1 @@
+function(){return Promise.resolve();}
\ No newline at end of file
diff --git a/tests/empty function/input.js b/tests/empty function/input.js
new file mode 100644
index 0000000..ec22ed3
--- /dev/null
+++ b/tests/empty function/input.js	
@@ -0,0 +1,2 @@
+async function() {
+}
diff --git a/tests/empty function/output.js b/tests/empty function/output.js
new file mode 100644
index 0000000..8d5e13d
--- /dev/null
+++ b/tests/empty function/output.js	
@@ -0,0 +1 @@
+()=>_await()
\ No newline at end of file