Re: [PATCH] add unused flag check arguments to toolchain flag detection

[Rich Felker <dalias@libc.org>]

On Thu, May 28, 2015 at 04:50:10AM +0200, Shiz wrote:
> 
> this checks whether -Werror=unknown-warning-option and
> -Werror=unused-command-line-argument are supported by the toolchain. if so,
> it adds those flags to the tryflag and tryldflag checks in ./configure.
> 
> so far only clang supports these flags, but clang is also the only toolchain
> I've encountered that ignores unrecognized arguments instead of erroring out.
> ---
>  configure | 14 ++++++++++++--
>  1 file changed, 12 insertions(+), 2 deletions(-)

Thanks! The patch looks mostly good (except the -Wl, part that's
wrong). I have some proposed changes to the message. The shortlog
message should be clear on the what and where of the change:

configure: work around compilers that only warn for unknown options

Then, if not already clear, the body should express more about why and
how, such as:

some compilers (such as clang) accept unknown options without error,
but then print warnings on each invocation, cluttering the build
output and burying meaningful warnings. this patch makes configure's
tryflag and tryldflag functions use additional options to turn the
unknown-option warnings into errors, if available, but only at check
time. these options are not output in config.mak to avoid the risk of
spurious build breakage; if they work, they will have already done
their job at configure time.

FYI cparser/firm also supports -Werror=unknown-warning-option so it's
not just clang.

Rich