GNU bug report logs - #20831
`missing` script handling of broken timestamps

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From: Karl Berry <karl <at> freefriends.org>
To: eblake <at> redhat.com
Cc: m4-discuss <at> gnu.org, 20831 <at> debbugs.gnu.org, gchengordon <at> gmail.com
Subject: bug#20831: Can m4 be built without automake?
Date: Tue, 25 Feb 2025 10:14:25 -0700

Hi Eric and all - back on this report from 2015 (sorry):

    https://debbugs.gnu.org/cgi/bugreport.cgi?bug=20831

    This is a regression in behavior in upstream automake.  It means
    that any automake-generated file that is unpacked with timestamp skew
    will now fail to build

Yes. I'm afraid this is a wontfix. Stefano L wrote a long description of
why he changed the behavior of missing to no longer touch files (copied
below).

I'm not sure I entirely buy it, but it wasn't just a capricious change,
and I'm not inclined to reverse it and go back to the problems that the
"touch version" of missing had. Especially since this report is 10 years
old, not followed up on, and no other reports have surfaced, as far as
far as I can remmber.

Best,
karl


2012-06-21  Stefano Lattarini  <stefano.lattarini <at> gmail.com>

	missing: do not touch timestamps; only warn for out-of-date files

	Before this change, the missing script had a twofold role:

	  - it warned the user if some required maintainer tools was missing,
	    or too old;

	  - in such a case, it tried to "fix" the timestamp of the files that
	    should have been rebuilt by that tool (without actually updating
	    the file contents, of course), to allow the build to continue.

	The second capability used to be quite useful in the days when most
	projects committed files generated by maintainer-only tools in their
	VCS repository (today the trend is not to keep such generated files
	VCS-committed anymore).  In such a setup, the "timestamp-fixing"
	capability of 'missing' was quite useful, in that it allowed users
	lacking some required maintainer tool to build from a VCS checkout
	in the face of skewed timestamps (as could have been caused by
	"cvs update" or "git checkout").

	But then, when the automatic remake rules kicked in due to the
	generated files being *actually out-of-date* (e.g., because the user
	had modified 'configure.ac' but lacked a modern-enough autoconf to
	rebuild it), that behaviour of 'missing' caused the same problem that
	plagued AM_MAINTAINER_MODE; i.e., the user would get non-dependable
	builds and inconsistent statuses of the build tree -- changes to
	source files don't reflect on generated files, and this can be very
	confusing and cause hard-to-spot errors).

	So we now believe that the best approach to deal with timestamp-related
	issues is not to have 'missing' to "automagically" try to resolve
	them (with all the risk and brittleness entailed), but rather to
	suggest those projects still keeping generated files committed in their
	VCS to provide a proper (say) 'fix-timestamp.sh' script that touches
	the timestamp of the checked-out files, to ensure no spurious rebuild
	will be triggered.  As a bonus, such a script can be more aware of the
	particularities, nooks and corner cases of a project, and thus more
	reliable than the old 'missing' script.

	An example of this approach is offered by GNU awk (release 4.0.1, Git
	tag 'gawk-4.0.1', commit b85b04e8).  The GNU awk maintainers commit
	the Autotools-generated files (configure, Makefile.in, etc.) and other
	generated in the project's Git repository, but offer a useful script
	'bootstrap.sh' that fixes the timestamps of those files, to ensure no
	useless remake is triggered in a freshly cloned repository:

	    #! /bin/sh
	    # bootstrap.sh --- touch relevant files to avoid out-of-date issues
	    #                  in Git sandboxes
	    touch aclocal.m4
	    find awklib -type f -print | xargs touch
	    sleep 1
	    touch configure
	    sleep 2
	    touch configh.in
	    sleep 1
	    touch test/Maketests
	    find . -name Makefile.in -print | xargs touch
	    touch doc/*.info
	    touch po/*.gmo
	    touch po/stamp-po
	    touch awkgram.c
	    touch command.c
	    touch version.c

	A similar, simplified script is also reported as an example in the
	manual.

	* NEWS: Update.
	* doc/automake.texi (Auxiliary Programs, maintainer-mod): Update.
	(CVS): Do not suggest that 'missing' can "automagically" fix botched
	timestamp due to a "cvs update"; this isn't true anymore.  Give an
	example of a custom 'fix-timestamp.sh' script that can be used to
	obtain the same effect (in a slightly more laborious but also more
	explicit and less brittle way).  Fix some minor typos and improper
	wordings while we are at it.
	* lib/missing: Basically rewritten to implement the new semantics.
	As a side effect (one of the several), the '--run' option is no more
	required nor recognized.
	* m4/missing.m4 (AM_MISSING_HAS_RUN): Enhance the test on '$MISSING'
	to ensure it actually provides the new semantics (by trying the new
	"witness" option '--is-lightweight').
	* lib/am/distdir.am (distdir): No need anymore to check for "bad"
	distributed man pages that were actually dummy stubs generated by
	the 'missing' script.
	* t/missing4.sh: Rename ...
	* t/remake-aclocal-version-mismatch.sh: ... like this.
	* t/missing2.sh: Rename ...
	* t/missing-version-mismatch.sh: ... like this, and adjust to the
	new semantics.
	* t/missing3.sh: Adjust to the new semantics.
	* t/man4.sh: Remove as obsolete.
	* t/missing.sh: Likewise.
	* t/missing5.sh: Likewise.
	* t/txinfo30.sh: Likewise.
	* t/man6.sh: Adjust grepping checks.
	* t/remake6.sh: Likewise.
	* t/list-of-tests.mk: Adjust.

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