Only base async fn arity on non-default/non-rest params - fixes #4891 (#4901)

packages/babel-plugin-transform-async-to-generator/test/fixtures/async-to-generator/function-arity/actual.js

@@ -0,0 +1,4 @@
+async function one(a, b = 1) {}
+async function two(a, b, ...c) {}
+async function three(a, b = 1, c, d = 3) {}
+async function four(a, b = 1, c, ...d) {}

packages/babel-plugin-transform-async-to-generator/test/fixtures/async-to-generator/function-arity/expected.js

@@ -0,0 +1,31 @@
+let one = (() => {
+  var _ref = babelHelpers.asyncToGenerator(function* (a, b = 1) {});
+
+  return function one(_x) {
+    return _ref.apply(this, arguments);
+  };
+})();
+
+let two = (() => {
+  var _ref2 = babelHelpers.asyncToGenerator(function* (a, b, ...c) {});
+
+  return function two(_x2, _x3) {
+    return _ref2.apply(this, arguments);
+  };
+})();
+
+let three = (() => {
+  var _ref3 = babelHelpers.asyncToGenerator(function* (a, b = 1, c, d = 3) {});
+
+  return function three(_x4) {
+    return _ref3.apply(this, arguments);
+  };
+})();
+
+let four = (() => {
+  var _ref4 = babelHelpers.asyncToGenerator(function* (a, b = 1, c, ...d) {});
+
+  return function four(_x5) {
+    return _ref4.apply(this, arguments);
+  };
+})();

packages/babel-plugin-transform-async-to-generator/test/fixtures/async-to-generator/function-arity/options.json

@@ -0,0 +1,6 @@
+{
+	"plugins": [
+		"transform-async-to-generator",
+		"external-helpers"
+	]
+}