Re: [PATCH v3 1/7] meson: Run some compiler checks using -Wno-unused-value

["Nicholas Piggin" <npiggin@gmail.com>]

On Thu Dec 19, 2024 at 4:21 AM AEST, Philippe Mathieu-Daudé wrote:
> When running Clang static analyzer on macOS I'm getting:
>
>   include/qemu/osdep.h:634:8: error: redefinition of 'iovec'
>     634 | struct iovec {
>         |        ^
>   /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/_types/_iovec_t.h:31:8: note: previous definition is here
>      31 | struct iovec {
>         |        ^
>   1 error generated.
>
> Looking at meson-logs.txt, the analyzer enables -Wunused-value
> making meson generated code to fail:
>
>     Code:
>     #include <sys/uio.h>
>             void bar(void) {
>                 sizeof(struct iovec);
>             }
>     -----------
>     stderr:
>     meson-private/tmpe8_1b_00/testfile.c:3:13: error: expression result unused [-Werror,-Wunused-value]
>         3 |             sizeof(struct iovec);
>           |             ^~~~~~~~~~~~~~~~~~~~
>     1 error generated.
>     -----------
>     Checking for type "struct iovec" : NO
>
>     Code:
>     #include <utmpx.h>
>             void bar(void) {
>                 sizeof(struct utmpx);
>             }
>     -----------
>     stderr:
>     meson-private/tmp3n0u490p/testfile.c:3:13: error: expression result unused [-Werror,-Wunused-value]
>         3 |             sizeof(struct utmpx);
>           |             ^~~~~~~~~~~~~~~~~~~~
>     1 error generated.
>     -----------
>     Checking for type "struct utmpx" : NO
>
>     Code:
>
>             #include <getopt.h>
>             int main(void) {
>                 /* If it's not defined as a macro, try to use as a symbol */
>                 #ifndef optreset
>                     optreset;
>                 #endif
>                 return 0;
>             }
>     -----------
>     stderr:
>     meson-private/tmp1rzob_os/testfile.c:6:17: error: expression result unused [-Werror,-Wunused-value]
>         6 |                 optreset;
>           |                 ^~~~~~~~
>     1 error generated.
>     -----------
>     Header "getopt.h" has symbol "optreset" : NO
>
>     Code:
>
>             #include <vmnet/vmnet.h>
>             int main(void) {
>                 /* If it's not defined as a macro, try to use as a symbol */
>                 #ifndef VMNET_BRIDGED_MODE
>                     VMNET_BRIDGED_MODE;
>                 #endif
>                 return 0;
>             }
>     -----------
>     stderr:
>     meson-private/tmpl9jgsxpt/testfile.c:6:17: error: expression result unused [-Werror,-Wunused-value]
>         6 |                 VMNET_BRIDGED_MODE;
>           |                 ^~~~~~~~~~~~~~~~~~
>     1 error generated.
>     -----------
>     Header "vmnet/vmnet.h" has symbol "VMNET_BRIDGED_MODE" with dependency appleframeworks: NO
>     ../meson.build:1174: WARNING: vmnet.framework API is outdated, disabling
>
> Fix by explicitly disabling -Wunused-value from these meson checks.
>
> Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
> ---
> RFC: Probably meson should do that in has_header_symbol() / has_type()?

I don't know about the build system to answer this, but should we
instead disable -Werror on these tests to be a bit more future-proof?
Compilers often add new warnings or catch more cases of existing
warnings.

Alternative would be to keep -Werror but fail the build if a test
throws a warning, but that seems like a lot more work for little
benefit...

Thanks,
Nick

> ---
>  meson.build | 11 +++++++----
>  1 file changed, 7 insertions(+), 4 deletions(-)
>
> diff --git a/meson.build b/meson.build
> index 85f74854735..9d93dcd95d7 100644
> --- a/meson.build
> +++ b/meson.build
> @@ -1189,7 +1189,8 @@ cocoa = dependency('appleframeworks',
>  vmnet = dependency('appleframeworks', modules: 'vmnet', required: get_option('vmnet'))
>  if vmnet.found() and not cc.has_header_symbol('vmnet/vmnet.h',
>                                                'VMNET_BRIDGED_MODE',
> -                                              dependencies: vmnet)
> +                                              dependencies: vmnet,
> +                                              args: '-Wno-unused-value')
>    vmnet = not_found
>    if get_option('vmnet').enabled()
>      error('vmnet.framework API is outdated')
> @@ -2713,7 +2714,7 @@ config_host_data.set('CONFIG_RTNETLINK',
>  config_host_data.set('CONFIG_SYSMACROS',
>                       cc.has_header_symbol('sys/sysmacros.h', 'makedev'))
>  config_host_data.set('HAVE_OPTRESET',
> -                     cc.has_header_symbol('getopt.h', 'optreset'))
> +                     cc.has_header_symbol('getopt.h', 'optreset', args: '-Wno-unused-value'))
>  config_host_data.set('HAVE_IPPROTO_MPTCP',
>                       cc.has_header_symbol('netinet/in.h', 'IPPROTO_MPTCP'))
>  
> @@ -2731,10 +2732,12 @@ config_host_data.set('HAVE_BLK_ZONE_REP_CAPACITY',
>  # has_type
>  config_host_data.set('CONFIG_IOVEC',
>                       cc.has_type('struct iovec',
> -                                 prefix: '#include <sys/uio.h>'))
> +                                 prefix: '#include <sys/uio.h>',
> +                                 args: '-Wno-unused-value'))
>  config_host_data.set('HAVE_UTMPX',
>                       cc.has_type('struct utmpx',
> -                                 prefix: '#include <utmpx.h>'))
> +                                 prefix: '#include <utmpx.h>',
> +                                 args: '-Wno-unused-value'))
>  
>  config_host_data.set('CONFIG_EVENTFD', cc.links('''
>    #include <sys/eventfd.h>