ReflectionFunctionAbstract->getParamInfo appending class name in default expressions to current namespace

[simonwelsh]

HHVM Version

3.22.1

Standalone code, or other way to reproduce the problem

<?hh

namespace Test {
    function dumpFoo(\Foo $foo = new \Foo()): void {
        var_dump($foo);
    }
}

namespace {
    class Foo {}

    $rf = new ReflectionFunction('Test\dumpFoo');
    var_dump($rf->getParameters());
}

Expected result

array(1) {
  [0]=>
  object(ReflectionParameter)#3 (3) {
    ["info"]=>
    array(11) {
      ["index"]=>
      int(0)
      ["name"]=>
      string(3) "foo"
      ["type"]=>
      string(3) "Foo"
      ["type_hint"]=>
      string(3) "Foo"
      ["type_hint_builtin"]=>
      bool(false)
      ["function"]=>
      string(7) "Test\dumpFoo"
      ["type_hint_nullable"]=>
      bool(false)
      ["default"]=>
      object(Test\Foo)#2 (0) {
      }
      ["defaultText"]=>
      string(9) "new \Foo()"
      ["attributes"]=>
      array(0) {
      }
      ["is_optional"]=>
      bool(true)
    }
    ["name"]=>
    string(3) "foo"
    ["paramTypeInfo"]=>
    array(3) {
      ["name"]=>
      string(3) "Foo"
      ["nullable"]=>
      bool(false)
      ["builtin"]=>
      bool(false)
    }
  }
}

Actual result

Fatal error: Uncaught Error: Class undefined: Test\Foo in :1
Stack trace:
#0 (): include()
#1 (): ReflectionFunctionAbstract->getParamInfo()
#2 /in/HCRR3(-1): ReflectionFunctionAbstract->getParameters()
#3 {main}