[clang] Missing diagnostic when initializing a member variable using uninitialized member variable

[horenmar]

I recently found an -Wreorder adjacent issue that does not get diagnosed. In the test_t struct below, we initialize bar using foo member variable, but because foo is declared after bar, we are reading it before initialization. (this can happen e.g. by reordering the member without noticing the dependency).

struct test_t {
  int bar{ foo + 1 };
  int foo{ 3 };
};

int main() {
    test_t t{};
}

CE link

Ideally this would also be caught under -Wreorder or by -Wuninitialized.

[firewave]

It is detected with -std=c++11 but not with -std=c++14 and up: https://godbolt.org/z/hxffTa3rd