Why doesn't clang -Wunused-member-function warn about an unused member function?

Question

I'm compiling a very basic program attempting to trigger output from -Wunused-member-function.

test.cpp:

#include <iostream>

class A {
    public:
    void foo() { std::cout << "Called foo" << std::endl; }
    void foo_unused() { std::cout << "Unused foo" << std::endl; }
};

int main() {
    A obj;
    obj.foo();
    return 0;
}

The output from the following command

clang++ -std=c++17 -Wall -Wunused -Wunused-member-function \
        -Wunused-function -Wunneeded-member-function \
        test.cpp -o test

unfortunately contained not even a single warning. I expected the compiler to warn about foo_unused not being used.

Is there a different behavior I'm missing here? Otherwise, why doesn't clang complain about the unused member function?

Answer 1

You have to put the class in an anonymous namespace to make the warning appear:

namespace
{
class A {
    public:
    void foo() { std::cout << "Called foo" << std::endl; }
    void foo_unused() { std::cout << "Unused foo" << std::endl; }
};
}

You can see that now you have the warning: https://godbolt.org/z/15Buo-

The reason is that this version can activate clang checks on public methods as well, as you explicitely said that this class will not be accessible in another translation unit.