[C++17][clang:Frontend] Clang can't deduce the correct deduction guide.

[HoBoIs]

If there are two auto generated deduction guides from a templated and a non templated constructor we should choose the guide generated from the non-templated constructor. But clang can't deduce which one should we use. (gcc can)

https://godbolt.org/z/ee3e9qG78

[HoBoIs]

The pull request #66487 Will solve the issue, once it is merged (It haven't been reviewed yet).

[llvmbot]

@llvm/issue-subscribers-c-17

If there are two auto generated deduction guides from a templated and a non templated constructor we should choose the guide generated from the non-templated constructor. But clang can't deduce which one should we use. (gcc can)

https://godbolt.org/z/ee3e9qG78

[llvmbot]

@llvm/issue-subscribers-clang-frontend

If there are two auto generated deduction guides from a templated and a non templated constructor we should choose the guide generated from the non-templated constructor. But clang can't deduce which one should we use. (gcc can)

https://godbolt.org/z/ee3e9qG78

[shafik]

It is helpful to include reasonably sized code snippets so readers can understand the issue report in once place:

template<class T>
struct A
{
    A(T, T, int);  //#1
 
    template<class U>
    A(int, T, U);  //#2
};                 
 
A x(1, 2, 3); // Should choose #1

This looks like overload resolution to me from over.match.best.general p2.13.

Looks like the wording came from p0620r0 which was about deduction guides but I don't see how the specific example is deduction guides but I may be missing something.

[HoBoIs]

You have to deduce the template parameter of A (to int) from the deduction guides generated from the constructors. The rule http://eel.is/c++draft/over.match.best.general#2.13 Says that the we have to use guide generated from the first constructor, but calng claims the deduction is ambigous.