Instantiation of class template causes instantiation of static data member's definition

[BobBugs]

According to C++20 [temp.inst]/3.1 the definition of static data member i should not be instantiated, and therefore the program must compile:

template <class T>
class C {
    static const int i = T::value;
};

C<void> x;

Clang 17.0.1 instantiates it, and compilation fails. Demo.

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: None (BobBugs)

According to C++20 [\[temp.inst\]/3.1](https://timsong-cpp.github.io/cppwp/n4868/temp.inst#3.1) the definition of static data member `i` should not be instantiated, and therefore the program must compile:

template <class T>
class C {
    static const int i = T::value;
};

C<void> x;

Clang 17.0.1 instantiates it, and compilation fails. Demo.

[shafik]

Note only gcc accepts: https://godbolt.org/z/KbY7h37bW

I think this is related to: #59966 (comment)

[zygoloid]

This example contains only a declaration, not a definition, of the static data member. The initializer is part of that declaration, so gets instantiated with the class.

I think clang is correct here.