parenthesise exported iifes correctly

lib/output.js

@@ -1106,6 +1106,20 @@ function OutputStream(options) {
         self._do_print(output);
     });
 
+    DEFPRINT(AST_Function, function(self, output) {
+        var parent = output.parent();
+        var grandparent = output.parent(1);
+        var is_exported_iife = parent instanceof AST_Call && parent.expression == self &&
+            grandparent instanceof AST_Export && grandparent.is_default;
+        if (is_exported_iife) {
+            output.with_parens(function() {
+                self._do_print(output);
+            });
+        } else {
+            self._do_print(output);
+        }
+    });
+
     DEFPRINT(AST_PrefixedTemplateString, function(self, output) {
         self.prefix.print(output);
         self.template_string.print(output);

test/compress/export.js

@@ -410,7 +410,7 @@ export_default_anonymous_function_not_call: {
         export default function(){}(foo);
     }
     // FIXME: should be `export default function(){};foo;`
-    expect_exact: "export default function(){}(foo);"
+    expect_exact: "export default(function(){})(foo);"
 }
 
 export_default_anonymous_generator_not_call: {

test/compress/issue-2977.js

@@ -0,0 +1,7 @@
+
+issue_2977: {
+    input: {
+        export default (function () {})();
+    }
+    expect_exact: "export default(function(){})();"
+}