support asynchronous arrow functions (#4530)

1 files changed, 14 insertions, 4 deletions

diff --git a/lib/output.js b/lib/output.js
index 9e704e8c..ae068462 100644
--- a/lib/output.js
+++ b/lib/output.js
@@ -692,7 +692,7 @@ function OutputStream(options) {
             // [ 1, (2, 3), 4 ] ==> [ 1, 3, 4 ]
         return p instanceof AST_Array
             // () => (foo, bar)
-            || p instanceof AST_Arrow && p.value === this
+            || is_arrow(p) && p.value === this
             // await (foo, bar)
             || p instanceof AST_Await
             // 1 + (2, 3) + 4 ==> 8
@@ -813,6 +813,9 @@ function OutputStream(options) {
         // ({ p: a } = o);
         if (this.left instanceof AST_DestructuredObject) return needs_parens_obj(output);
     });
+    PARENS(AST_AsyncArrow, function(output) {
+        return needs_parens_assign_cond(this, output);
+    });
     PARENS(AST_Conditional, function(output) {
         return needs_parens_assign_cond(this, output);
     });
@@ -1005,8 +1008,7 @@ function OutputStream(options) {
             }
         });
     }
-    DEFPRINT(AST_Arrow, function(output) {
-        var self = this;
+    function print_arrow(self, output) {
         if (self.argnames.length == 1 && self.argnames[0] instanceof AST_SymbolFunarg && !self.rest) {
             self.argnames[0].print(output);
         } else {
@@ -1020,6 +1022,14 @@ function OutputStream(options) {
         } else {
             print_braced(self, output, true);
         }
+    }
+    DEFPRINT(AST_Arrow, function(output) {
+        print_arrow(this, output);
+    });
+    DEFPRINT(AST_AsyncArrow, function(output) {
+        output.print("async");
+        output.space();
+        print_arrow(this, output);
     });
     function print_lambda(self, output) {
         if (self.name) {
@@ -1207,7 +1217,7 @@ function OutputStream(options) {
         if (noin) node.walk(new TreeWalker(function(node) {
             if (parens) return true;
             if (node instanceof AST_Binary && node.operator == "in") return parens = true;
-            if (node instanceof AST_Scope && !(node instanceof AST_Arrow && node.value)) return true;
+            if (node instanceof AST_Scope && !(is_arrow(node) && node.value)) return true;
         }));
         node.print(output, parens);
     }