Always retain lines for async arrow (#11836)

packages/babel-generator/src/generators/methods.js

@@ -112,7 +112,7 @@ export function ArrowFunctionExpression(node: Object) {
     !hasTypes(node, firstParam)
   ) {
     if (
-      this.format.retainLines &&
+      (this.format.retainLines || node.async) &&
       node.loc &&
       node.body.loc &&
       node.loc.start.line < node.body.loc.start.line

packages/babel-generator/test/fixtures/parentheses/async-arrow-function/input.js

@@ -0,0 +1,10 @@
+const x = async (
+  // some comment
+  a
+) => {
+  return foo(await a);
+};
+
+function foo(a) {
+  return a;
+}

packages/babel-generator/test/fixtures/parentheses/async-arrow-function/options.json

@@ -0,0 +1 @@
+{}

packages/babel-generator/test/fixtures/parentheses/async-arrow-function/output.js

@@ -0,0 +1,8 @@
+const x = async ( // some comment
+  a) => {
+  return foo(await a);
+};
+
+function foo(a) {
+  return a;
+}