[Clang] Valid candidate template function seems to be overlooked during explicit instantiation with specialized template class

[wangbo15]

Consider the following example:

template <class T>
struct A
{
    void f(T) {}
    template <typename MUT> void f(MUT t){}
};

template<>
struct A<int>
{
    void f(int) {}
    template <typename MUT> void f(MUT t){}
};

template
void A<int>::f(int);

Here the template function template<typename MUT> void f(MUT t) seems to be a feasible candidate for the explicit template function instantiation, but clang does not notice that:

<source>:16:14: error: explicit instantiation refers to member function 'A<int>::f' that is not an instantiation
   16 | void A<int>::f(int);
      |              ^
<source>:11:10: note: explicit instantiation refers here
   11 |     void f(int) {}
      |          ^
1 error generated.

GCC, EDG, and MSVC accept that: https://godbolt.org/z/qs1Tcr5s6

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: Bo Wang (wangbo15)

Consider the following example:

template <class T>
struct A
{
    void f(T) {}
    template <typename MUT> void f(MUT t){}
};

template<>
struct A<int>
{
    void f(int) {}
    template <typename MUT> void f(MUT t){}
};

template
void A<int>::f(int);

Here the template function template<typename MUT> void f(MUT t) seems to be a feasible candidate for the explicit template function instantiation, but clang does not notice that:

<source>:16:14: error: explicit instantiation refers to member function 'A<int>::f' that is not an instantiation
   16 | void A<int>::f(int);
      |              ^
<source>:11:10: note: explicit instantiation refers here
   11 |     void f(int) {}
      |          ^
1 error generated.

GCC, EDG, and MSVC accept that: https://godbolt.org/z/qs1Tcr5s6

[shafik]

I think this should work but interesting to note that if you comment out the specialization then gcc is the only one to reject: https://godbolt.org/z/6P3Y8zxhE

[cor3ntin]

This appear to be https://www.open-std.org/jtc1/sc22/wg21/docs/cwg_active.html#1665 @zygoloid