Re: Feature request: Add --mtime option to git archive

From: Jeff King <peff@peff.net>
Date: Feb 16, 2023, 21:05 UTC
Message-ID: <Y+6akicTFG9n0eZy@coredump.intra.peff.net>
In-Reply-To: <Y+6G9n6cWRT9EKyl@google.com>

On Thu, Feb 16, 2023 at 12:41:42PM -0700, Raul E Rangel wrote:

> When generating a tarball with `git archive <tree>`, `git archive` will
> use the current time as the mtime. This results in a non-hermetic
> tarball. Could we should add a --mtime option that allows passing in
> the time?

That seems like a very reasonable feature to have. Just to sketch out the implementation, in case anybody wants to work on it:

  - options are read first in cmd_archive(), but it passes unknown ones
    on to write_archive(), which is where we parse the interesting ones.

  - that relies on parse_archive_args() in archive.c. So we'd want a new
    option in opts[] there, and to write the value into a new field in
    the archiver_args struct.

  - the time is filled in via parse_treeish_arg(), where we use
    time(NULL) if there's no commit. And there we'd just use the value
    from archiver_args.

    If there is a commit and they've specified --mtime, what should
    happen? Quietly ignore it? Override the commit's timestamp? Complain
    and bail?

  - I didn't look at how this might interact with "git archive
    --remote". I think it might just all work, as we just ship the
    options to the other side, which parses them itself using the same
    code.

-Peff