[Mesa-dev] [PATCH] m4: add Werror when checking for compiler flags

[Dylan Baker]

Quoting Emil Velikov (2018-10-24 10:57:00)
> Seemingly that at some point clang started accepting _any_ flags,
> whereas previously it would error out.
> 
> These days, you can give it -Whamsandwich and it will succeed, while
> at the same time throwing an annoying warning.
> 
> Add -Werror so that everything gets flagged and set accordingly.
> 
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=108082
> Cc: Eric Engestrom <eric.engestrom at intel.com>
> Cc: Dylan Baker <dylan at pnwbakers.com>
> Cc: Vinson Lee <vlee at freedesktop.org>
> Repored-by: Vinson Lee <vlee at freedesktop.org>
> Signed-off-by: Emil Velikov <emil.velikov at collabora.com>
> ---
>  m4/ax_check_compile_flag.m4 | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/m4/ax_check_compile_flag.m4 b/m4/ax_check_compile_flag.m4
> index 51df0c09a7a..0fdca907e8b 100644
> --- a/m4/ax_check_compile_flag.m4
> +++ b/m4/ax_check_compile_flag.m4
> @@ -55,6 +55,11 @@
>  #   modified version of the Autoconf Macro, you may extend this special
>  #   exception to the GPL to apply to your modified version as well.
>  
> +# Emil:
> +# Toggle Werror since at some point clang started treating unknown -W
> +# flags as warnings, succeeding with the build, yet issuing an annoying
> +# warning.
> +
>  #serial 3
>  
>  AC_DEFUN([AX_CHECK_COMPILE_FLAG],
> @@ -62,7 +67,7 @@ AC_DEFUN([AX_CHECK_COMPILE_FLAG],
>  AS_VAR_PUSHDEF([CACHEVAR],[ax_cv_check_[]_AC_LANG_ABBREV[]flags_$4_$1])dnl
>  AC_CACHE_CHECK([whether _AC_LANG compiler accepts $1], CACHEVAR, [
>    ax_check_save_flags=$[]_AC_LANG_PREFIX[]FLAGS
> -  _AC_LANG_PREFIX[]FLAGS="$[]_AC_LANG_PREFIX[]FLAGS $4 $1"
> +  _AC_LANG_PREFIX[]FLAGS="$[]_AC_LANG_PREFIX[]FLAGS $4 $1 -Werror"
>    AC_COMPILE_IFELSE([m4_default([$5],[AC_LANG_PROGRAM()])],
>      [AS_VAR_SET(CACHEVAR,[yes])],
>      [AS_VAR_SET(CACHEVAR,[no])])
> -- 
> 2.19.1
> 

This seems like the most straightforward way to solve the issue, since otherwise
you need to track which compiler you have.

Reviewed-by: Dylan Baker <dylan at pnwbakers.com>
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