Re: [PATCH 1/4] include: Add macro to ignore -Wuser-defined-warnings

[Tsukasa OI <research_trasio@irq.a4lg.com>]

On 2022/09/21 1:36, Nick Clifton wrote:
> Hi Tsukasa,
> 
>> +# if __has_warning ("-Wuser-defined-warnings")
> 
> I have not seen __has_warning () before.  Is this a new feature of
> recent GCCs and Clang, or am I just behind the times ?

Nick, this is one of the Clang language extensions:
<https://clang.llvm.org/docs/LanguageExtensions.html#include-file-checking-macros>

and already used in Binutils, include/diagnostics.h:58 (latest master)

    # if __has_warning ("-Wenum-compare-switch")

This and my new line with __has_warning are surrounded by "#if defined
(__clang__)" (a Clang-only part of the code) and should not expand to a
non-zero value unless:

1.  __has_warning is implemented as either a Clang extension
    or a custom macro (I will not assume this for obvious reasons).
2.  Builtin __has_warning (as I assumed above) detects given warning
    is implemented.

__has_warning is a Clang extension but similar standard feature testing
macros with arguments are defined in recent C++ versions (not usable as
standard language features in Binutils, though):

-   __has_include (C++17 or later)
-   __has_cpp_attribute (C++20 or later)

Thanks,
Tsukasa

> 
> Cheers
>   Nick
>