generator: remove redundant async tests

lib/6to5/generators/methods.js

@@ -1,24 +1,53 @@
 exports._params = function (node, print) {
+  var self = this;
+
   this.push("(");
-  this.printJoin(print, node.params, ", ");
+
+  this.printJoin(print, node.params, ", ", {
+    iterator: function (param, i) {
+      print(param);
+
+      var def = node.defaults && node.defaults[i];
+      if (def) {
+        self.push(" = ");
+        print(def);
+      }
+    }
+  });
+
+  if (node.rest) {
+    if (node.params.length) {
+      this.push(", ");
+    }
+
+    this.push("...");
+    print(node.rest);
+  }
+
   this.push(")");
 };
 
-exports._method = function (kind, key, value, print) {
-  if (value.async) {
-    this.push("async ");
-  }
+exports._method = function (node, print) {
+  var value = node.value;
+  var kind  = node.kind;
+  var key   = node.key;
 
   if (!kind || kind === "init") {
     if (value.generator) {
       this.push("*");
     }
   } else {
-    assert.ok(kind === "get" || kind === "set");
     this.push(kind + " ");
   }
 
-  print(key);
+  if (node.computed) {
+    this.push("[");
+    print(key);
+    this.push("]");
+  } else {
+    print(key);
+  }
+
   this._params(value, print);
   print(value.body);
 };
@@ -28,12 +57,7 @@ exports.MethodDefinition = function (node, print) {
     this.push("static ");
   }
 
-  this._method(
-    node.kind,
-    node.key,
-    node.value,
-    print
-  );
+  this._method(node, print);
 };
 
 exports.ReturnStatement = function (node, print) {
@@ -42,12 +66,11 @@ exports.ReturnStatement = function (node, print) {
     this.push(" ");
     print(node.argument);
   }
-  this.push(";");
+  this.semicolon();
 };
 
 exports.FunctionDeclaration =
 exports.FunctionExpression = function (node, print) {
-  if (node.async) this.push("async ");
   this.push("function");
   if (node.generator) this.push("*");
   if (node.id) {
@@ -61,12 +84,12 @@ exports.FunctionExpression = function (node, print) {
 };
 
 exports.ArrowFunctionExpression = function (node, print) {
-  if (node.async) this.push("async ");
-  if (node.params.length === 1) {
+  if (node.params.length === 1 && !node.defaults.length && !node.rest && node.params[0].type === "Identifier") {
     print(node.params[0]);
   } else {
     this._params(node, print);
   }
+
   this.push(" => ");
   print(node.body);
 };