Re: (bug?) Inconsistent workdir file timestamps after initial clone.

From: Junio C Hamano <gitster@pobox.com>
Date: Dec 11, 2012, 21:27 UTC
Message-ID: <7vy5h47003.fsf@alter.siamese.dyndns.org>
In-Reply-To: <50C79D1F.1080709@xiplink.com>

Marc Branchaud <marcnarc@xiplink.com> writes:

Show 11 quoted lines

> Occasionally when doing a fresh clone of a repo, if the clock ticks at just
> the wrong time the checked-out files end up with different timestamps.
>
> The effect of this can be that, when "make" is run in the workdir it'll
> decide that some files are out of date and try to rebuild them.
>
> (In our particular case, our automated build-bot cloned a submodule of some
> third-party (i.e. not our) code, where a Makefile.in got an earlier timestamp
> than its dependent Makefile.am, so "configure && make" then tried to rebuild
> Makefile.in and the build failed because our build environment has the wrong
> version of automake.)

Even if you somehow arrange Makefile.in and Makefile.am to have the same timestamp, wouldn't it be up to your "make" to decide which one is newer? Certainly Makefile.in is not newer than Makefile.am, and it is free to try rebuilding it.

Also if you do this after any operation:

    $ rm Makefile.am
    $ git checkout Makefile.am

you will have Makefile.am that is newer than your Makefile.in and you will end up attempting to rebuild it.

The timestamp of a working tree file records the time at which it was created in your working tree. It does not have any relation to the commit or author timestamp of the commit you check it out of. If this command:

    $ git checkout @{1.dacade.ago} Makefile.am

gave your Makefile.am an ancient timestamp, it will break your build.

While not including files that can be rebuilt from the source may be the ideal solution, I've seen projects hide rules to rebuild such a "generated but needs special tools to build" and/or a "generated but normal developers do not have any business rebuilding" file (in your case, Makefile.in) in their Makefiles from the normal targets (like "make all") for this exact reason, when they choose to distribute such files by including in their commits.