Erase the invokers

Summary: [Folly] Erase the invokers. A catchy title, but forcibly inline the invoker call operators.

Reviewed By: vitaut

Differential Revision: D18035184

fbshipit-source-id: 5cf57d785523904a5260f7ed24c9ed34148370eb

folly/CPortability.h

@@ -196,6 +196,20 @@
 //  Semantically includes the inline specifier.
 #define FOLLY_ERASE FOLLY_ALWAYS_INLINE FOLLY_ATTR_VISIBILITY_HIDDEN
 
+//  FOLLY_ERASE_HACK_GCC
+//
+//  Equivalent to FOLLY_ERASE, but without hiding under gcc. Useful when applied
+//  to a function which may sometimes be hidden separately, for example by being
+//  declared in an anonymous namespace, since in such cases with -Wattributes
+//  enabled, gcc would emit: 'visibility' attribute ignored.
+//
+//  Semantically includes the inline specifier.
+#if defined(__GNUC__) && !defined(__clang__)
+#define FOLLY_ERASE_HACK_GCC FOLLY_ALWAYS_INLINE
+#else
+#define FOLLY_ERASE_HACK_GCC FOLLY_ERASE
+#endif
+
 //  FOLLY_ERASE_TRYCATCH
 //
 //  Equivalent to FOLLY_ERASE, but for code which might contain explicit

folly/functional/Invoke.h

@@ -57,13 +57,13 @@ namespace folly {
 
 //  mimic: std::invoke, C++17
 template <typename F, typename... Args>
-constexpr auto invoke(F&& f, Args&&... args) noexcept(
+FOLLY_ERASE constexpr auto invoke(F&& f, Args&&... args) noexcept(
     noexcept(static_cast<F&&>(f)(static_cast<Args&&>(args)...)))
     -> decltype(static_cast<F&&>(f)(static_cast<Args&&>(args)...)) {
   return static_cast<F&&>(f)(static_cast<Args&&>(args)...);
 }
 template <typename M, typename C, typename... Args>
-constexpr auto invoke(M(C::*d), Args&&... args)
+FOLLY_ERASE constexpr auto invoke(M(C::*d), Args&&... args)
     -> decltype(std::mem_fn(d)(static_cast<Args&&>(args)...)) {
   return std::mem_fn(d)(static_cast<Args&&>(args)...);
 }
@@ -363,7 +363,7 @@ struct invoke_traits : detail::invoke_traits_base<Invoke> {
     FOLLY_DETAIL_CREATE_FREE_INVOKE_TRAITS_USING(_, funcname, __VA_ARGS__) \
     struct __folly_detail_invoke_obj {                                     \
       template <typename... Args>                                          \
-      constexpr auto operator()(Args&&... args) const                      \
+      FOLLY_ERASE_HACK_GCC constexpr auto operator()(Args&&... args) const \
           noexcept(noexcept(funcname(static_cast<Args&&>(args)...)))       \
               -> decltype(funcname(static_cast<Args&&>(args)...)) {        \
         return funcname(static_cast<Args&&>(args)...);                     \
@@ -416,10 +416,11 @@ struct invoke_traits : detail::invoke_traits_base<Invoke> {
 #define FOLLY_CREATE_MEMBER_INVOKER(classname, membername)                 \
   struct classname {                                                       \
     template <typename O, typename... Args>                                \
-    constexpr auto operator()(O&& o, Args&&... args) const noexcept(noexcept( \
+    FOLLY_ERASE_HACK_GCC constexpr auto operator()(O&& o, Args&&... args)  \
+        const noexcept(noexcept(                                           \
             static_cast<O&&>(o).membername(static_cast<Args&&>(args)...))) \
-        -> decltype(                                                          \
-            static_cast<O&&>(o).membername(static_cast<Args&&>(args)...)) {   \
+            -> decltype(static_cast<O&&>(o).membername(                    \
+                static_cast<Args&&>(args)...)) {                           \
       return static_cast<O&&>(o).membername(static_cast<Args&&>(args)...); \
     }                                                                      \
   }