git non-time-sequential logs

[John Baldwin]

On 1/4/21 8:52 AM, John Kennedy wrote:
> On Mon, Jan 04, 2021 at 08:22:56AM -0800, John Kennedy wrote:
>> The git logs in /usr/src aren't time-sequential, so maybe I shouldn't trust
>> those dates above (I pulled it ~Jan 3rd and let it compile overnight), but
>> I'm going to repull all the sources and recompile, just in case.  I might
>> have initiall pulled it during the git conversion and maybe it is confused.
> 
> This might be perfectly natural and just new to me, but when I look at the
> git logs this morning I see things like this (editing by me):
> 
> 	commit e5df46055add3bcf074c9ba275ceb4481802ba04 (HEAD -> main, freebsd/main, freebsd/HEAD)
> 	Author: Emmanuel Vadot <manu at FreeBSD.org>
> 	Date:   Mon Jan 4 17:30:00 2021 +0100
> 
> 	commit f61a3898bb989edef7ca308043224e495ed78f64
> 	Author: Emmanuel Vadot <manu at freebsd.org>
> 	Date:   Mon Dec 14 18:56:56 2020 +0100
> 
> 	commit b6cc69322a77fa778b00db873781be04f26bd2ee
> 	Author: Emmanuel Vadot <manu at freebsd.org>
> 	Date:   Tue Dec 15 13:50:00 2020 +0100
> 
> 	commit 4401fa9bf1a3f2a7f2ca04fae9291218e1ca56bf
> 	Author: Emmanuel Vadot <manu at FreeBSD.org>
> 	Date:   Mon Jan 4 16:23:10 2021 +0100
> 
>   This is a fresh clone+pull off of anongit at git.FreeBSD.org:src.git.
> 
>   I've always assumed that the "Date:" there was when the commit happened,
> so they'd be increasing (most recent on top), but I suppose that you might
> have developers in branches that are committing to their branch at one
> point in time and it's getting merged into current (main) later, but the
> original date is preserved?
> 
>   I guess I only care because I was trying to use time to bisect the
> time I thought the problem might have been introduced.

For commits to gdb (which uses git), the project asks that all series be
rebased via 'git rebase --ignore-date' prior to pushing to master to give
monotonically increasing commit dates.  We could do something similar in
FreeBSD either by asking folks to do that explicitly (though I know I
sometimes forget when pushing to gdb myself), or we could avoid direct
pushes to main.  One option some folks mentioned on IRC was to have a
separate "staging" branch that developers push to and then have a bot that
does a rebase --ignore-date of that branch to main periodically, though
that opens the question of how to deal with cherry-picks to stable (for
which asking developers to do a rebase --ignore-date prior to pushing is
probably the simpler approach).

If we did want monotonically increasing dates without having a staging
branch, we could perhaps use a server-side push hook to reject them and
developers would just have to do a rebase --ignore-date before pushing
again.

-- 
John Baldwin