Throwing exception uses incorrect copy constructor

[JVApen]

Bugzilla Link	38801
Version	7.0
OS	Windows NT
CC	@zmodem,@JVApen

Extended Description

Hello all,

The following code seems to have problems being executed.
It looks like when throwing an exception, Clang tries to use a copy constructor for the exception, however, instead of using the const& variant, it searches for a variant without the const.
So instead of using the Copy constructor, it uses the variadic Ctor, which is not as expected.

test.cpp

struct A
{
   template<typename ... T>
   A(T &&...t)
   {
      static_assert(sizeof...(T) == 2);
   }
   
   A(const A &) = default;
   //A(A &) = default;
   A(A &&) = default;
   A &operator=(const A &) = default;
   A &operator=(A &&) = default;
};


int main(int, char **)
{
   throw A{size_t{}, size_t{}};
   return 0;
}

run.bat

clang-cl.exe -fms-compatibility-version=19.11 /DBOOST_USE_WINDOWS_H -w -Wno-unused-command-line-argument /Zc:inline /nologo /c /GR /EHsc /fp:precise /FS /std:c++17 /diagnostics:caret /O2 /I. /MDd /Zc:forScope /bigobj /Zc:wchar_t test.cpp

error

test.cpp(7,7):  error: static_assert failed
      static_assert(sizeof...(T) == 2);
      ^             ~~~~~~~~~~~~~~~~~
test.cpp(20,10):  note: in instantiation of function template specialization 'A::A<A &>' requested here
   throw A{size_t{}, size_t{}};
         ^
1 error generated.

[JVApen]

Question: Any chance the fix can still be part of LLVM 7.0.0?

[JVApen]

Correcting 'enhancement' to 'normal' issue. This ain't a feature request.

[zmodem]

This does not seem to be getting fixed for clang 10, and I don't think we can block on it.

[llvmbot]

@llvm/issue-subscribers-clang-frontend

[llvmbot]

@llvm/issue-subscribers-c-1

[AaronBallman]

This issue reproduces in Clang 16.0.0, only for Win32 targets, and it does not match the behavior of MSVC: https://godbolt.org/z/KsbfPE74q