async arrow function IIFE fix (#2184)

fixes #2183

lib/compress.js

@@ -561,8 +561,8 @@ merge(Compressor.prototype, {
         return orig.length == 1 && orig[0] instanceof AST_SymbolLambda;
     });
 
-    function is_func_expr(node) {
-        return node instanceof AST_Arrow || node instanceof AST_Function;
+    function is_func_expr(node, traditional) {
+        return node instanceof AST_Function || !traditional && node instanceof AST_Arrow;
     }
 
     function is_lhs_read_only(lhs) {
@@ -706,9 +706,9 @@ merge(Compressor.prototype, {
         return x;
     };
 
-    function is_iife_call(node) {
+    function is_iife_call(node, traditional) {
         if (node instanceof AST_Call && !(node instanceof AST_New)) {
-            return is_func_expr(node.expression) || is_iife_call(node.expression);
+            return is_func_expr(node.expression, traditional) || is_iife_call(node.expression);
         }
         return false;
     }
@@ -3452,7 +3452,7 @@ merge(Compressor.prototype, {
         }
         if (compressor.option("negate_iife")
             && compressor.parent() instanceof AST_SimpleStatement
-            && is_iife_call(self)) {
+            && is_iife_call(self, true)) {
             return self.negate(compressor, true);
         }
         var ev = self.evaluate(compressor);

lib/output.js

@@ -1045,11 +1045,11 @@ function OutputStream(options) {
         var needs_parens = parent instanceof AST_Binary ||
             parent instanceof AST_Unary ||
             (parent instanceof AST_Call && self === parent.expression);
+        if (needs_parens) { output.print("(") }
         if (self.async) {
             output.print("async");
             output.space();
         }
-        if (needs_parens) { output.print("(") }
         if (self.argnames.length === 1 && self.argnames[0] instanceof AST_Symbol) {
             self.argnames[0].print(output);
         } else {

test/compress/async.js

@@ -268,3 +268,27 @@ async_arrow_wait: {
     }
     expect_exact: "var a=async(x,y)=>await x(y);"
 }
+
+async_arrow_iife: {
+    input: {
+        (async () => {
+            await fetch({});
+        })();
+    }
+    expect_exact: "(async()=>{await fetch({})})();"
+}
+
+async_arrow_iife_negate_iife: {
+    options = {
+        negate_iife: true,
+    }
+    input: {
+        (async () => {
+            await fetch();
+        })();
+        (() => {
+            plain();
+        })();
+    }
+    expect_exact: "(async()=>{await fetch()})();(()=>{plain()})();"
+}