[Automake-commit] [SCM] GNU Automake branch, experimental/missing-not-touch-just-warn, created. v1.12.1-87-g8feee5e

[Stefano Lattarini]

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http://git.sv.gnu.org/gitweb/?p=automake.git;a=commitdiff;h=8feee5ec1c2fa3bde2c2ba242b03bdde97d58b47

The branch, experimental/missing-not-touch-just-warn has been created
        at  8feee5ec1c2fa3bde2c2ba242b03bdde97d58b47 (commit)

- Log -----------------------------------------------------------------
commit 8feee5ec1c2fa3bde2c2ba242b03bdde97d58b47
Author: Stefano Lattarini <address@hidden>
Date:   Fri Jun 15 11:13:00 2012 +0200

    missing: do not touch timestamps; only warn for out-of-date files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    generated files being *actually out-of-date* (e.g., because the user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 (albeit
    IMHO poorly named) 'bootstrap.sh' script that fixes the timestamps of
    those files, to ensure no useless remake is triggered in a freshly
    clones 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
    
    Signed-off-by: Stefano Lattarini <address@hidden>

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