Re: [PATCH-for-8.0] block/dmg: Ignore C99 prototype declaration mismatch from <lzfse.h>

["Philippe Mathieu-Daudé" <philmd@linaro.org>]

On 28/3/23 08:29, Stefan Weil wrote:
> Am 27.03.23 um 23:09 schrieb Paolo Bonzini:
> 
>> Il lun 27 mar 2023, 20:58 Philippe Mathieu-Daudé <philmd@linaro.org> 
>> ha scritto:
>>
>>     > The warning can also be suppressed if the build uses `-isystem
>>     > /opt/homebrew/include` instead of `-I/opt/homebrew/include` as I
>>     just
>>     > have tested.
>>
>> Is that option added by QEMU's configure or meson.build? Or is it 
>> added by homebrew? The fact that /opt/homebrew/include it isn't 
>> considered a system seems to be a homebrew decision.
>>
>>     IIUC by design meson only allows including *relative* directories,
>>     and manage the system ones:
>>     https://mesonbuild.com/Include-directories.html
>>
>> That's for includes that are part of QEMU.
>>
>> Meson has as_system for dependency objects 
>> (https://mesonbuild.com/Reference-manual_returned_dep.html) but lzfse 
>> doesn't have a .pc file, its detection has to be done by hand.
>>
>> Paolo
>>
>>     > If we can find a solution how to implement that I thing it would
>>     look
>>     > nicer. Technically the patch looks good.
>>     >
>>     > Reviewed-by: Stefan Weil <sw@weilnetz.de>
>>
>>     Thanks!
>>
> 
> Typically I configure the build on macOS with `./configure 
> --extra-cflags=-I/opt/homebrew/include 
> --extra-ldflags=-L/opt/homebrew/lib --disable-werror`. With that 
> configuration I get the two warnings for lzfse.h.
> 
> When I use `./configure '--extra-cflags=-isystem /opt/homebrew/include' 
> --extra-ldflags=-L/opt/homebrew/lib --disable-werror` instead, I get no 
> compiler warnings (and `--disable-werror` could be ommitted).
> 
> So at least for macOS with Homebrew in /opt/homebrew (M1 / M2 Macs) the 
> patch is not needed when the right configure options (`--extra-cflags`) 
> were used.

What I learned:

- If lzfse were well packaged (as noted Paolo), we could use
   dependency(..., include_type: 'system')
   https://github.com/mesonbuild/meson/issues/963#issuecomment-1277851401

- I agree with Eli Schwartz, a Meson maintainer:

   > More bugs caused by and only affecting people who misuse and
   > abuse -isystem as "not system, but as a side effect please
   > don't emit warnings for this messy dependency"...

   https://github.com/mesonbuild/meson/issues/8755#issuecomment-836913759

I wasted few hours on this, and am now giving up in favor of this simple
patch.