[RFC PATCH 0/6] Work around autoconf/automake warnings skew

[Zack Weinberg]

autoreconf runs a bunch of subsidiary tools, and is expected to pass
along various command-line settings, such as those controlling
warnings.  It has historically done this via the command line.
However, not all of the tools recognize the same set of command-line
warnings options.  There’s an existing check for whether aclocal and
automake understand ‘--warnings’ at all, but it currently assumes that
automake will accept the same set of warnings *categories* that
autoconf does.  This hasn’t actually been true for many years
and is known to cause problems; see the discussion starting at
<https://lists.gnu.org/archive/html/autoconf/2020-09/msg00000.html>.

This patch set makes the changes on autoconf’s side required to bring
ChannelDefs.pm back into sync between autoconf and automake, which
makes the set of categories consistent for future releases.  It also
implements a workaround in autoreconf, to avoid problems with
inconsistent *installed* versions of autoconf and automake: we pass
warnings options to subsidiary tools using the WARNINGS environment
variable instead of on the command line.  Unsupported categories in
WARNINGS have always been ignored, so the problem is eliminated.

I manually verified that, with the combination of trunk autoconf and
released automake 1.16, one can run autoreconf -Werror,cross without
any problems.  With autoreconf from 2.69, by contrast, aclocal will
bomb out.

The main thing I want to discuss before merging these patches is the
location of the new Perl function merge_WARNINGS.  I put it in
ChannelDefs.pm because that is where all the other code relating to
WARNINGS is, but it’s only used in autoreconf, so there’s an argument
for putting it in autoreconf instead, if only so we can modify it in
the future without having to go through automake.

Side effects include:

 - The ‘obsolete’ category of warnings is now on by default
   (automake has already made this change).
 - More of autoreconf’s subsidiary tools may generate warnings now.
   Specifically, we were not passing -W options to autopoint,
   libtoolize, intltool, or gtkdocize, but they will all see the
   WARNINGS environment variable.  I don’t know if any of them
   pay attention to it.
 - All of the commands that run autoconf or autom4te in --trace mode
   also set WARNINGS=none in the environment.  This means, most
   visibly, that autoheader no longer repeats autoconf’s warnings.
 - We are now autoupdating a bunch of obsolete diagnostics-related
   macros.  This is just something I happened to notice because I was
   messing with code near them.

N.B. I have not yet added ChannelDefs.pm to the list of files to sync
from automake.  I will do that in a separate commit after all the dust
settles from this patchset.

zw
-- 

Zack Weinberg (6):
  Manually sync ChannelDefs.pm from automake.
  New utility function Autom4te::ChannelDefs::merge_WARNINGS.
  Disable all warnings when running autoconf as a subprocess.
  Use WARNINGS to pass down warnings options from autoreconf.
  Update documentation related to warnings.
  Autoupdate AC_{DIAGNOSE,FATAL,OBSOLETE,WARNING} and _AC_COMPUTE_INT.

 NEWS                        |  13 ++
 bin/autoconf.as             |  21 ++-
 bin/autoheader.in           |  31 ++--
 bin/autom4te.in             |  10 +-
 bin/autoreconf.in           |  87 ++++++-----
 bin/autoscan.in             |   5 +-
 bin/autoupdate.in           |   5 +
 doc/autoconf.texi           | 287 ++++++++++++++++--------------------
 lib/Autom4te/ChannelDefs.pm | 237 ++++++++++++++++++++++++-----
 lib/Autom4te/Config.pm      |  43 ++++++
 lib/autoconf/autoupdate.m4  |  14 +-
 lib/autoconf/c.m4           |   2 +-
 lib/autoconf/functions.m4   |   8 +-
 lib/autoconf/general.m4     |  78 +++++-----
 lib/autoconf/headers.m4     |   8 +-
 lib/autoconf/lang.m4        |   2 +-
 lib/autoconf/specific.m4    |   2 +-
 lib/autoconf/status.m4      |   6 +-
 lib/autoconf/types.m4       |   4 +-
 lib/autom4te.in             |   1 -
 lib/local.mk                |   1 +
 tests/base.at               |   2 +-
 tests/c.at                  |   2 +-
 tests/compile.at            |   7 +-
 tests/local.at              |  48 +++---
 tests/m4sh.at               |   2 +-
 tests/m4sugar.at            |  25 ++--
 tests/mktests.sh            |  10 +-
 tests/semantics.at          |  48 +++---
 tests/tools.at              | 179 +++++++++++++++++++++-
 tests/torture.at            |  64 ++++++--
 31 files changed, 831 insertions(+), 421 deletions(-)
 create mode 100644 lib/Autom4te/Config.pm

-- 
2.28.0