[llvm-bugs] [Bug 35063] New: libc++ says my user-defined type has an operator<< during sfinae - libstdc++ works as expected

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=35063

            Bug ID: 35063
           Summary: libc++ says my user-defined type has an operator<<
                    during sfinae - libstdc++ works as expected
           Product: libc++
           Version: unspecified
          Hardware: PC
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: All Bugs
          Assignee: unassignedclangbugs at nondot.org
          Reporter: xaxxon at gmail.com
                CC: llvm-bugs at lists.llvm.org, mclow.lists at gmail.com

https://godbolt.org/g/PRfyjH

#include <type_traits>                                                          
#include <iostream>                                                             

template<typename T, typename = void>                                           
struct has_insertion_operator : std::false_type {};                             

template<typename T>                                                            
struct has_insertion_operator<T,                                                
                              std::void_t<decltype(                             
                                                  
operator<<(std::declval<std::ostream>(),                                        
                                                             
std::declval<T>()))>                                                            
                                  > : std::true_type {};                        

template<class T>                                                               
constexpr bool has_insertion_operator_v = has_insertion_operator<T>::value;     

class A{};                                                                      
static_assert(!has_insertion_operator_v<A>);  // <== I expect this to pass, but
it fires on libc++.

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