[PATCH] c++: Add new warning options for C++ language mismatches

[Marek Polacek]

On Wed, May 19, 2021 at 05:39:24PM +0100, Jonathan Wakely via Gcc-patches wrote:
> Jakub pointed out I'd forgotten the spaces before the opening parens
> for function calls. The attached patch should fix all those, with no
> other changes.
> 
> Tested x86_64-linux. OK for trunk?

Nice, this is cool.

> --- a/gcc/c-family/c.opt
> +++ b/gcc/c-family/c.opt
> @@ -431,6 +431,22 @@ Wc++20-compat
>  C++ ObjC++ Var(warn_cxx20_compat) Warning LangEnabledBy(C++ ObjC++,Wall)
>  Warn about C++ constructs whose meaning differs between ISO C++ 2017 and ISO C++ 2020.
>  
> +Wc++11-extensions
> +C++ ObjC++ Var(warn_cxx11_extensions) Warning LangEnabledBy(C++ ObjC++,Wall) Init(1)
> +Warn about C++11 constructs in code compiled with an older standard.
> +
> +Wc++14-extensions
> +C++ ObjC++ Var(warn_cxx14_extensions) Warning LangEnabledBy(C++ ObjC++,Wall) Init(1)
> +Warn about C++14 constructs in code compiled with an older standard.
> +
> +Wc++17-extensions
> +C++ ObjC++ Var(warn_cxx17_extensions) Warning LangEnabledBy(C++ ObjC++,Wall) Init(1)
> +Warn about C++17 constructs in code compiled with an older standard.
> +
> +Wc++20-extensions
> +C++ ObjC++ Var(warn_cxx20_extensions) Warning LangEnabledBy(C++ ObjC++,Wall) Init(1)
> +Warn about C++20 constructs in code compiled with an older standard.
> +

So these are enabled by -Wall but also turned on by default?  Let's choose one
and then drop either the Init(1) or the LangEnabledBy(C++ ObjC++,Wall) part?

Marek