[clang-tidy] readability-container-size-empty fails to detect calls to member functions

[vbvictor]

Given code:

void bar();

class foo {
  int size() const;
  bool empty() const;

  void doit() {
    if (!size())
      bar();
  }
};

Should warn to use empty() instead of !size() but it doesn't.
https://godbolt.org/z/feGTc8vPo

[llvmbot]

@llvm/issue-subscribers-clang-tidy

Author: Baranov Victor (vbvictor)

Given code: ```cpp void bar();

class foo {
int size() const;
bool empty() const;

void doit() {
if (!size())
bar();
}
};

Should warn to use `empty()` instead of `!size()` but it doesn't.
https://godbolt.org/z/feGTc8vPo
</details>

[chrchr-github]

Looks like warnings are only generated for external calls to the size() member (might make sense in case empty() is implemented using size()):
https://godbolt.org/z/rdae5dGWh

[vbvictor]

With #152486, the check will correctly warn on size() members that come from inheritance. I don't see immediate blocker why can't we detect in-class member-functions.

[flovent]

This commit avoid further checking for size in whole container itself's defintion, but it only add testcase for size using in empty, maybe we should only avoid checking in empty.

[vbvictor]

maybe we should only avoid checking in empty.

+1 here, I don't see pitfalls in it for now.