[boost] [type_traits] Variadic function pointer with __fastcall calling convention

Subject: [boost] [type_traits] Variadic function pointer with __fastcall calling convention
From: Edward Diener (eldiener_at_[hidden])
Date: 2013-10-01 21:09:21

In type_traits/detail/is_function_ptr_tester.hpp there are pointer to 
function signatures being tested which have the __fastcall calling 
convention and variadic functions. While MSVC accepts this code clang in 
Windows, which defines _MSC_VER and _MSC_EXTENSIONS, currently gives an 
error. The justification for giving an error is that __fastcall is a 
callee stack cleanup calling convention, so it cannot be used for 
variadic functions.

There is a bug report regarding this in the Bugzilla for llvm at 
http://llvm.org/bugs/show_bug.cgi?id=12535.

Comments have been made to me in e-mail and the clang developer's 
mailing list that it is a type_traits error to allow this, even for 
MSVC-emulation code. Of course we can temporarily fix this for clang on 
Windows, possibly with a BOOST_WORKAROUND solution for clang and see 
if/how clang eventually addresses the bug report. But I would like some 
sort of resolution so that clang on Windows can compile type_traits in 
the current Boost trunk.