Clang accepts invalid program when default constructor is overloaded with initializer list constructor that is also a default constructor

[ranaanoop]

The following invalid program is accepted by clang. Demo

#include <initializer_list>

struct C
{ 
    C(){}
    C(std::initializer_list<int> i = {3})
    {
    }  
};

int main()
{
    C d{};   //clang:Ok, gcc:No, MSVC: No, EDG: No
}

This is invalid due to ambiguity between the ctors for () as explained in this thread.

Clang uses the initializer list ctor over the other default ctor which is not the correct behavior.

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: Anoop Rana (ranaanoop)

The following [invalid](https://stackoverflow.com/questions/78836456/overloaded-default-constructor-with-initializer-list-constructor-that-is-also-a) program is accepted by clang. [Demo](https://godbolt.org/z/8nn1Pc3rz)

#include <initializer_list>

struct C
{ 
    C(){}
    C(std::initializer_list<int> i = {3})
    {
    }  
};

int main()
{
    C d{};   //clang:Ok, gcc:No, MSVC: No, EDG: No
}

This is invalid due to ambiguity between the ctors for () as explained in this thread.

Clang uses the initializer list ctor over the other default ctor which is not the correct behavior.