Re: [PULL 00/21] Plugins patches for 2026-01-29

["Daniel P. Berrangé" <berrange@redhat.com>]

On Mon, Feb 02, 2026 at 09:30:31AM -0800, Pierrick Bouvier wrote:
> On 2/2/26 8:55 AM, Mark Cave-Ayland wrote:
> > On 02/02/2026 15:42, Cornelia Huck wrote:
> > 
> > > On Mon, Feb 02 2026, Peter Maydell <peter.maydell@linaro.org> wrote:
> > > 
> > > > On Mon, 2 Feb 2026 at 04:04, Richard Henderson
> > > > <richard.henderson@linaro.org> wrote:
> > > > > 
> > > > > On 1/30/26 04:41, Pierrick Bouvier wrote:
> > > > > > On 1/29/26 9:37 AM, Pierrick Bouvier wrote:
> > > > > > >          contrib/plugins: add empty cpp plugin
> > > > 
> > > > Hi; this fails to build for me on Linux (Ubuntu 24.04) with clang:
> > > > 
> > > > In file included from ../../contrib/plugins/cpp.cpp:33:
> > > > /usr/bin/../lib/gcc/x86_64-linux-gnu/14/../../../../include/c++/14/coroutine:38:3:
> > > > error: "the <coroutine> header requires -fcoroutines"
> > > >      38 | # error "the <coroutine> header requires -fcoroutines"
> > > >         |   ^
> > > > 1 error generated.
> > > 
> > > Fails for me as well on Fedora 42 (x86_64) with gcc:
> > > 
> > > In file included from ../qemu/contrib/plugins/cpp.cpp:33:
> > > /usr/include/c++/15/coroutine:43:3: error: #error "the <coroutine> header requires -fcoroutines"
> > >      43 | # error "the <coroutine> header requires -fcoroutines"
> > >         |   ^~~~~
> > > 
> > > (It works for me on an aarch64 RHEL 9 system.)
> > 
> > Is this with a clean build? I had exactly the same error message
> > earlier, but I was able to fix it by destroying my build/ directory,
> > then re-running configure followed again by make.
> > 
> 
> Thanks for the reports everyone.
> 
> I tried it on ubuntu LTS and didn't encounter this problem.
> What is happening is that meson unfortunately caches default_options set,
> including the C++ standard version in our case.
> Thus, you indeed need to clean and rebuild once.
> 
> The solution for this would be to not use default_options and add the flag
> to qemu_cflags instead. It's the same limitation if we change the default
> warning level, or any other option set with default_options.

If that's correct as the root cause, then it feels like this is a meson bug
that ought to be reported upstream. Any meson.build default_options changes
that affect the compiler behaviour should invalidate cache in the same way
as when we modify qemu_cflags.

With regards,
Daniel
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