Compiler error for requires expression with templated base class member function

[rath3t]

The following code fails to compile with clang trunk and clang 16 (See godbolt link).
The templated member function is not found by clang and therefore the static_assert is triggered.

The struct A inherits from T and therefore the base class member function foo exists, thus the static_assert should not trigger.
It works for non-templated base class member functions though.

struct B {
    template <typename S>
    void foo();

    void bar();
};

template <typename T, typename S>
struct A : T {
    auto foo() {
        static_assert(requires { T::template foo<S>(); });  // fails with clang
        static_assert(requires { T::bar(); });  // works with clang and gcc 12.2
    }
};

int main() {
    A<B, double> a;
    a.foo();
}

Godbolt

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: Alex_Mueller (rath3t)

The following code fails to compile with clang trunk and clang 16 (See godbolt link). The templated member function is not found by clang and therefore the `static_assert` is triggered.

The struct A inherits from T and therefore the base class member function foo exists, thus the static_assert should not trigger.
It works for non-templated base class member functions though.

struct B {
    template <typename S>
    void foo();

    void bar();
};

template <typename T, typename S>
struct A : T {
    auto foo() {
        static_assert(requires { T::template foo<S>(); });  // fails with clang
        static_assert(requires { T::bar(); });  // works with clang and gcc 12.2
    }
};

int main() {
    A<B, double> a;
    a.foo();
}

Godbolt

[llvmbot]

@llvm/issue-subscribers-c-20

Author: Alex_Mueller (rath3t)

The following code fails to compile with clang trunk and clang 16 (See godbolt link). The templated member function is not found by clang and therefore the `static_assert` is triggered.

The struct A inherits from T and therefore the base class member function foo exists, thus the static_assert should not trigger.
It works for non-templated base class member functions though.

struct B {
    template <typename S>
    void foo();

    void bar();
};

template <typename T, typename S>
struct A : T {
    auto foo() {
        static_assert(requires { T::template foo<S>(); });  // fails with clang
        static_assert(requires { T::bar(); });  // works with clang and gcc 12.2
    }
};

int main() {
    A<B, double> a;
    a.foo();
}

Godbolt

[shafik]

EDG reject both but MSVC accepts both: https://godbolt.org/z/7G8rPY9hz

I don't see why they should be rejected but not totally sure.

CC @erichkeane @cor3ntin

[erichkeane]

I don't have a good idea, but both lookups seem to me like they should work.

[Sirraide]

At a glance, this looks like it’s a duplicate of #83979?

[rath3t]

Ah yes somebody copied my stackoverflow post https://stackoverflow.com/questions/78106241/compiler-divergence-in-delayed-template-instantiation.

[cor3ntin]

@shafik I agree with Erich, both lookup should work.

[shafik]

Ah yes somebody copied my stackoverflow post https://stackoverflow.com/questions/78106241/compiler-divergence-in-delayed-template-instantiation.

In the future it is helpful to link to Stackoverflow bugs, especially if someone on the committee already analyzed the bug then that makes screening a lot faster and we can get to more bugs.