RE: AC_FLAGS_WARN_ALL changes proposed for inclusion in next autoconf release

[Visser, Dale]

Mr. Eggert:

It is quite similar to the modules you mention. It is important to note that 
here AC_FLAGS_WARN_ALL is by default being invoked by the macros that set 
compilers for C, C++ or Fortran. From the documentation changes, it is 
described how this may be turned off:

     ‘AC_FLAGS_WARN_ALL’ is invoked by ‘AC_PROG_CC’, ‘AC_PROG_CXX’, and
     ‘AC_PROG_FC’ by default.  The addition of the detected default
     warning flags is controlled by the "default_warning_flags" feature,
     which is enabled by default.  It may be disabled with an option
     passed to the generated configure script.  To suppress the actual
     addition of any default warning flags in the configure.ac file,
     i.e., to restore the behavior from previous versions of autoconf,
     add the following line before you invoke ‘AC_FLAGS_WARN_ALL’,
     whether explicitly or implicitly:

          enable_default_warning_flags={enable_default_warning_flags:-no}

Also, AC_FLAGS_WARN_ALL makes an attempt to detect what compiler it is working 
with and sets the default warnings flag accordingly:

Compiler               Warning Flags Added
--------               -------------------
Intel                  -Wall -w3
GCC                    -Wall
Solaric C              -v
Digital Unix           -verbose -w0
AIX                    -gsrcmsg
IRIX                   -fullwarn
HP-UX C                +w1
NEC SX-5 (Super-UX 10) -pvctl[,]fullmsg
Cray C (Unicos)        -h msglevel 2

Besides the "off switch" mentioned above, specific warning flags may be 
set/unset using the provided macros AC_APPEND_xxxFLAG_IFVALID as well, which 
was adapted from the gnulib warnings module you asked about, as it happens.

My understanding was that all of the code I adapted was already under projects 
hosted Gnu, and so the copyright requirements had already been satisfied. I 
have given credit in the code comments wherever said code was adapted. I'm 
hoping Mr. Blake can speak authoritatively on this, as I am not an expert on 
the copyright aspects.

Best regards,
Dale Visser

-----Original Message-----
From: Paul Eggert [mailto:address@hidden 
Sent: Friday, September 05, 2014 6:25 PM
To: Visser, Dale; address@hidden
Subject: Re: AC_FLAGS_WARN_ALL changes proposed for inclusion in next autoconf 
release

Thanks for getting the ball rolling on this.  A couple of thoughts.

First, how does this compare to the warnings and manywarnings modules of 
Gnulib?  They seem to do something similar.  See:

http://www.gnu.org/software/gnulib/manual/html_node/warnings.html

http://www.gnu.org/software/gnulib/manual/html_node/manywarnings.html

Second, from a brief look at the patch it appears that it is derived from code 
that other people have written, which would mean we'd need to get copyright 
papers from them too.