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

From: Zack Weinberg
Subject: Re: Turn on compiler warnings by default for AC_PROG_CC, AC_PROG_CXX & AC_PROG_FC
Date: Fri, 17 Jan 2014 17:21:09 -0500
User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.6; rv:24.0) Gecko/20100101 Thunderbird/24.0.1

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

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.


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