Re: Turn on compiler warnings by default for AC_PROG_CC, AC_PROG_CXX & AC_PROG_FC

[Zack Weinberg]

On 2014-01-17 4:02 PM, David A. Wheeler wrote:
> Zack Weinberg said:
> > For GCC I would be quite hesitant to turn anything on beyond -Wall
> > without explicit buy-in from the project, but I like the idea of
> > enabling -Wall by default.
>
> I pretty sure that's what Dale Visser's patch does.  It says: +
> "-pedantic  % -Wall"       dnl GCC
>
> Dale Visser's patch does include a comment that says: +#   For the
> GNU compiler it will be -Wall (and -ansi -pedantic) The result +#
> is added to the shellvar being CFLAGS, CXXFLAGS, or FCFLAGS by
> default.
>
> But I think this comment is no longer true. It appears to me that the
> code is just trying to see if "-pedantic" *WORKS*, and if it does,
> then using that as evidence that "-Wall" would work.

Oh, is that what "-pedantic % -Wall" means?  I had the impression it was 
going to try each one in isolation and include the subset that worked.

Despite the dire things the GCC manual says about -pedantic, it is not 
hard to write *new* code that is -pedantic clean, or -Wextra clean, etc; 
I would support an opt-in mechanism for enabling a much more aggressive 
set of warnings, and recommending its use in the manual for new 
projects.  But any such thing has a high probability of breaking *old* 
code, hence my earlier comments.  Also, as long as stock Autoconf checks 
are sloppy (e.g. AC_CHECK_FUNCS and its habit of blindly declaring 
everything as "char foo();") we will need to distinguish warnings 
enabled for the *project* from warnings enabled for the *configure script*.

-ansi, however, should not be in there at all; it doesn't just turn on 
strict conformance mode, it turns on strict *C89* conformance mode, 
which is often wrong for new code.  And even nowadays, strict 
conformance mode in general tends to break system headers.

zw