let FOLLY_TYPE_INFO_OF always use its arg

Summary: Even when RTTI is disabled, to avoid unused-arg warnings. Then use `FOLLY_TYPE_INFO_OF` to simplify the conditional compilation in `UniqueInstance`.

Reviewed By: praihan

Differential Revision: D30183405

fbshipit-source-id: 040d90751822dedb8faca561a89dcf35da25119b

folly/detail/UniqueInstance.h

@@ -20,7 +20,6 @@
 #include <typeinfo>
 
 #include <folly/CppAttributes.h>
-#include <folly/Portability.h>
 #include <folly/detail/StaticSingletonManager.h>
 
 namespace folly {
@@ -28,14 +27,15 @@ namespace detail {
 
 class UniqueInstance {
  public:
-#if !FOLLY_HAS_RTTI || (__GNUC__ && __GNUC__ < 7 && !__clang__)
+#if __GNUC__ && __GNUC__ < 7 && !__clang__
   explicit UniqueInstance(...) noexcept {}
 #else
   template <template <typename...> class Z, typename... Key, typename... Mapped>
   FOLLY_EXPORT FOLLY_ALWAYS_INLINE explicit UniqueInstance(
       tag_t<Z<Key..., Mapped...>>, tag_t<Key...>, tag_t<Mapped...>) noexcept {
-    static Ptr const tmpl = &typeid(key_t<Z>);
-    static Ptr const ptrs[] = {&typeid(Key)..., &typeid(Mapped)...};
+    static Ptr const tmpl = FOLLY_TYPE_INFO_OF(key_t<Z>);
+    static Ptr const ptrs[] = {
+        FOLLY_TYPE_INFO_OF(Key)..., FOLLY_TYPE_INFO_OF(Mapped)...};
     static Arg arg{
         {tmpl, ptrs, sizeof...(Key), sizeof...(Mapped)},
         {tag<Value, key_t<Z, Key...>>}};

folly/lang/TypeInfo.h

@@ -28,7 +28,8 @@
 #if FOLLY_HAS_RTTI
 #define FOLLY_TYPE_INFO_OF(...) (&typeid(__VA_ARGS__))
 #else
-#define FOLLY_TYPE_INFO_OF(...) (static_cast<std::type_info const*>(nullptr))
+#define FOLLY_TYPE_INFO_OF(...) \
+  ((sizeof(__VA_ARGS__)), static_cast<std::type_info const*>(nullptr))
 #endif
 
 namespace folly {