C26434 Function xxx hides a non-virtual function - visual-c++

Question

Take this simple code:
void CRestoreSettingsDlg::OnSize(UINT nType, int cx, int cy)
{
CResizingDialog::OnSize(nType, cx, cy);
m_gridBackupLog.ExpandLastColumn();
}
Why is it being flagged?
C26434 Function 'CRestoreSettingsDlg::OnSize' hides a non-virtual function 'CRestoreDialogDlg::OnSize'.
As you can see, I call the base class method.
Declarations and Definitions
CRestoreSettingsDlg:
public:
afx_msg void OnSize(UINT nType, int cx, int cy);
void CRestoreSettingsDlg::OnSize(UINT nType, int cx, int cy)
{
CResizingDialog::OnSize(nType, cx, cy);
m_gridBackupLog.ExpandLastColumn();
}
CResizingDialog:
public:
afx_msg void OnSize(UINT nType, int cx, int cy);
void CResizingDialog::OnSize(UINT nType, int cx, int cy)
{
CDialogEx::OnSize(nType, cx, cy);
Invalidate(TRUE);
}
The boilerplate base class (afxwin.h) appears to have:
protected:
afx_msg void OnSize(UINT nType, int cx, int cy);
_AFXWIN_INLINE void CWnd::OnSize(UINT, int, int)
{ Default(); }
Inheritance
class CRestoreSettingsDlg : public CResizingDialog
class CResizingDialog : public CDialogEx

Answer 1

C26434 warning documentation links to C.128 C++ Core Guidelines Rule. It explains that to enforce correct usage of virtual functions, non-virtual function hiding should produce a warning.
However, with MFC message maps, you have to name your message handler as specified in macro, OnSize in this case, and, since message handlers already dispatched by a virtual function (that is hidden in *_MESSAGE_MAP() macros), message handler by themselves don't have to be virtual.
So it may be seen as a false alarm. Or maybe seen as violation of the above mentioned C.128 rule by MFC itself. No surprise - MFC is decades older than these guidelines.
So I guess you can go ahead and suppress it for all afx_msg functions. Maybe redefine afx_msg to include __pragma(warning(suppress(...))), or just have suppression around afx_msg block.
Some options for suppression (Godbolt's compiler explorer demo):
#define afx_msg // this is normally defined by MFC
struct base
{
afx_msg void OnSize(){}
};
struct derived1 : base
{
afx_msg void OnSize() {} // produces C26434
};
// Suppression by adding some code:
struct derived2 : base
{
#pragma warning(push)
#pragma warning(disable:26434)
afx_msg void OnSize() {}
#pragma warning(pop)
};
struct derived3 : base
{
[[gsl::suppress(c.128)]] afx_msg void OnSize() {}
};
// Suppression by redefining MFC macro -- dirty but less intrusive:
#undef afx_msg
#define afx_msg __pragma(warning(suppress:26434))
struct derived4 : base
{
afx_msg void OnSize() {}
};
#undef afx_msg
#define afx_msg [[gsl::suppress(c.128)]]
struct derived5 : base
{
afx_msg void OnSize() {}
};