// a.h
template <typename A, typename B>
struct is_base_of {
    constexpr static bool value = __is_base_of(A, B);
};
template <class Base, class Derived>
inline constexpr bool is_base_of_v = is_base_of<Base, Derived>::value;

// b.cc
#include "a.h"

class Foo {};
template <typename T>
struct Bar {
    static const bool y = is_base_of_v<T, Foo>;
};
bool foo() { return Bar<Foo>::y; }

$ ./include-what-you-use b.cc -std=c++20
b.cc should add these lines:

b.cc should remove these lines:
- #include "a.h"  // lines 1-1

The full include-list for b.cc:
---