GCC : Unscoped enumeration type give an ambiguity error

Question

In the following code, I have defined an unscoped enumeration with long long type. This program works fine on Clang.

But GCC compiler gives an ambiguity error.

#include <iostream>

enum : long long { Var=5 };

void fun(long long ll)
{
    std::cout << "long long : " << ll << std::endl;
}

void fun(int i)
{
    std::cout << "int : " << i <<  std::endl;
}

int main()
{
    fun(Var);
}

GCC generated error :

main.cpp: In function 'int main()':
main.cpp:17:12: error: call of overloaded 'fun(<unnamed enum>)' is ambiguous
     fun(Var);
            ^
main.cpp:5:6: note: candidate: void fun(long long int)
 void fun(long long ll)
      ^~~
main.cpp:10:6: note: candidate: void fun(int)
 void fun(int i)
      ^~~

Why does GCC compiler give an ambiguity error?

Answer 1

GCC is wrong.

Unscoped enumeration type converting to its underlying type is qualified as integral promotion:

an unscoped enumeration type whose underlying type is fixed can be converted to its underlying type, ... (since C++11)

While for Var converting to int it requires one more integral conversion (from long long to int). Integral promotion has higher ranking than integral conversion in overload resolution:

2) Promotion: integral promotion, floating-point promotion

3) Conversion: integral conversion, floating-point conversion, floating-integral conversion, pointer conversion, pointer-to-member conversion, boolean conversion, user-defined conversion of a derived class to its base

Then fun(long long ll) should be better match.

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Here's the gcc bug report; it's been fixed at 2017-10-24. LIVE