Make XHPAsync implement the XHPAwaitable trait

Slightly reduces boilerplate, and it's just a marker interface.

Author: fredemmott

src/core/XHPAsync.php

@@ -9,10 +9,8 @@
  *
  */
 
-trait XHPAsync {
-
+trait XHPAsync implements XHPAwaitable {
   require extends :x:element;
-  require implements XHPAwaitable;
 
   abstract protected function asyncRender(): Awaitable<XHPRoot>;
 

tests/AsyncTest.php

@@ -1,6 +1,6 @@
 <?hh
 
-class :async:test extends :x:element implements XHPAwaitable {
+class :async:test extends :x:element {
   use XHPAsync;
 
   protected async function asyncRender(): Awaitable<XHPRoot> {
@@ -39,4 +39,9 @@ public function testNestedWithNonAsyncChild() {
     $xhp = <async:test><b>BE BOLD</b></async:test>;
     $this->assertEquals('<div><b>BE BOLD</b></div>', $xhp->toString());
   }
+
+  public function testInstanceOfInterface() {
+    $xhp = <async:test><b>BE BOLD</b></async:test>;
+    $this->assertInstanceOf(XHPAwaitable::class, $xhp);
+  }
 }