[Bug c++/68144] New: operator~ in trailing return type leads to spurrious error

[Bug c++/68144] New: operator~ in trailing return type leads to spurrious error

[joel.falcou at lri dot fr]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68144

            Bug ID: 68144
           Summary: operator~ in trailing return type leads to spurrious
                    error
           Product: gcc
           Version: 5.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: joel.falcou at lri dot fr
  Target Milestone: ---

THe following code :

#include <iostream>

struct bar
{
  template<typename T> 
  auto operator()(T const& a) const -> decltype(~a) { return ~a; }
};

int main()
{  
  // works
  std::cout << ~1 << std::endl;

  // doesnt work
  bar z;  
  std::cout << z(1) << std::endl;
} 

Fails on g++ 5.2.0 with the following error:

main.cpp: In substitution of 'template<class T> decltype (~ a)
bar::operator()(const T&) const [with T = int]':
main.cpp:15:19:   required from here
main.cpp:5:29: error: 'a' was not declared in this scope


Changing -> decltype(~a) to -> decltype(~(a)) fixes this incorrect behavior.

Clang++ currently compiles this code correctly.