[PATCH] D29877: Warn about unused static file scope function template declarations.

[Vassil Vassilev via cfe-commits]

On 11/04/17 22:25, Richard Smith wrote:
> On 11 April 2017 at 08:35, Marshall Clow via Phabricator via 
> cfe-commits <cfe-commits at lists.llvm.org 
> <mailto:cfe-commits at lists.llvm.org>> wrote:
>
>     mclow.lists added a comment.
>
>     Complete reproducer:
>
>     // Tested with with:  clang++ -std=c++14 -Wunused-function
>     UnusedFVassily.cpp
>     //
>     // UnusedFVassily.cpp:8:39: warning: unused function '__test'
>     [-Wunused-function]
>     //     template <class _Up> static __two __test(...);
>     //                                       ^
>     // UnusedFVassily.cpp:9:38: warning: unused function '__test'
>     [-Wunused-function]
>     //     template <class _Up> static char __test(typename
>     _Up::pointer* = 0);
>     //                                      ^
>     // 2 warnings generated.
>
>     #include <type_traits>
>
>     namespace foo {
>
>     struct __two {char __lx; char __lxx;};
>     namespace __has_pointer_type_imp
>     {
>
>       template <class _Up> static __two __test(...);
>       template <class _Up> static char __test(typename _Up::pointer* = 0);
>
>     }
>
>     template <class _Tp>
>     struct __has_pointer_type
>
>       : public std::integral_constant<bool,
>     sizeof(__has_pointer_type_imp::__test<_Tp>(0)) == 1>
>
>
> This is a bug in libc++. If this header is included into two 
> translation units, they will be referencing different __test functions 
> here (because the template has internal linkage due to the 'static'), 
> resulting in an ODR violation.
Richard, shall we warn on template definitions marked static? This would 
keep this pattern still working.
>
>
>     {
>     };
>
>     }
>
>     struct S1 {};
>     struct S2 { typedef void *pointer; };
>
>     int main () {
>             static_assert (!foo::__has_pointer_type<S1>::value, "" );
>             static_assert ( foo::__has_pointer_type<S2>::value, "" );
>     }
>
>
>     https://reviews.llvm.org/D29877 <https://reviews.llvm.org/D29877>
>
>
>
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