test.cpp

class A {
public:
    virtual void foo(int a, int b = 1) = 0;
};

class B : public A {
public:
    void foo(int a, int) {
    }
};

int main() {
    B b;
    b.foo(1);
    return 0;
}

with this small change, it works, which should be the case in our codebase:

class A {
public:
    virtual void foo(int a, int b = 1) = 0;
};

class B : public A {
public:
    void foo(int a, int) {
    }
};

int main() {
    A *b = new B();
    b->foo(1);
    return 0;
}