Re: commit 9d0f14

[Mojca M. <moj...@gm...>]

On 22 March 2018 at 19:26, Ethan Merritt wrote:
>
> Here's a different idea.
> Does git gurantee to preserve the modification date attribute of files in
> the repository?

I'm not sure what you are asking exactly, but:

- Git doesn't remember original modification time of any file. That
is: you cannot take a file that was last modified on March 1st, commit
it today, clone repository and get that info about the 1st of March in
any way. The original modification timestamp is lost.
- What git *does* remember is commit timestamp, or rather two
timestamps, timestamp of when the author committed this first and then
another timestamp in case of further
modifications/merging/rebasing/cherry-picking etc. (git calls that
"author" and "committer" timestamp; you can manually specify those
timestamps of course, but that's a different issue)

When you switch back and forth between branches, the last modification
time of files on the disk will change, I think.

There is a way to enforce a consistent timing with a built-in function
to generate tarbals for example, but I don't think you can rely on
that feature unless you take some special care. By default all the
files you check out will have the timestamp of the time when you
cloned repository or pulled in new changes or switched between
branches rather than the timestamp of the actual change in repository.

> I observe that it does this in practice, but maybe it is not a guarantee.
> We don't really need to alter the _contents_ of a timestamp file,  just its
> modification date.

See above, I don't believe this would in practice be any less random
than the build timestamp. Ok, at least it will be reproducible on the
same machine, so slightly less randomness :)

Here are some ideas:
   https://stackoverflow.com/questions/1704907/how-can-i-get-my-c-code-to-automatically-print-out-its-git-version-hash

If the only problem of "git describe" is support for out-of-source
builds, couldn't the Makefile simply do something like

    # remember current build-dir
    cd source-dir
    version=`git describe ...`
    cd build-dir
    echo $version > versionfile.txt

(consider this to be pseudo-code). If git fails in this case, then go
for version written elsewhere of course.

Mojca