-Wundefined-func-template warns that no definition is available for a pure virtual function (original) (raw)

The warning seems incorrect as B::bar is pure virtual and its definition isn't needed.

template class B { public: constexpr void foo(const T &) { bar(1); } virtual constexpr void bar(unsigned int) = 0; };

template class D : public B { public: constexpr void bar(unsigned int) override {} };

void test() { auto t = D(); t.foo(0); }

$ clang++ -std=c++20 test.cpp -Wundefined-func-template -c
test.cpp:4:35: warning: instantiation of function 'B<int>::bar' required here, but no definition is available [-Wundefined-func-template]
  constexpr void foo(const T &) { bar(1); }
                                  ^
test.cpp:5:26: note: forward declaration of template entity is here
  virtual constexpr void bar(unsigned int) = 0;
                         ^
test.cpp:4:35: note: add an explicit instantiation declaration to suppress this warning if 'B<int>::bar' is explicitly instantiated in another translation unit
  constexpr void foo(const T &) { bar(1); }
                                  ^
1 warning generated.