Re: How to check out the repository at a particular point in time

From: Thomas Rast <trast@student.ethz.ch>
Date: Aug 23, 2011, 09:17 UTC
Message-ID: <201108231117.00314.trast@student.ethz.ch>
In-Reply-To: <1314085268.42103.YahooMailClassic@web25406.mail.ukl.yahoo.com>

R. Diez wrote:

> 
> check out HEAD, it should always work

Please stop using HEAD like this, you'll just confuse your coworkers (and yourself). HEAD denotes the currently checked out commit. [Unlike SVN it is *not* the most recent version of anything.] Thus by definition, 'git checkout HEAD' is a no-op.

The newest commit on a branch is denoted by its branch name, because as Jens said, a branch is in fact a pointer to its tip[1] commit.

> Now you're saying I cannot reliably checkout last week's versions
> because yesterday I did a merge from an older branch? You mean that
> git stores everything with clean graphs and numeric pointers, so it
> cannot know what this repository looked like last week?

Indeed. Especially if forced pushes are allowed, there is no way to know what was in the repo at a given time unless you have (local) reflogs enabled on remote branches and going back until the time you want.

Show 10 quoted lines

> As the developer, I have full control, I can decide what the
> branches are called and how the public repository is
> updated/pushed/whatever. I can control the clock so there are no
> time skews.
> 
> What do I have to do in order to be able to reliably checkout last
> week's versions without too much administrative work? I just want to
> get the same result today as if I had done a checkout last week from
> the public repository and had made a back-up copy of the working
> directory then.

Assuming

* you never do a non-fast-forward (i.e., forced) push
* you never have any clock skew
* you always merge features into master (not the other way around)
* you always push immediately after committing on master

you can get there by using 'git log -1 --first-parent --until=...' as mentioned in my first email.

I personally think that's crazy and -- if you want to avoid the work of "really" using submodules -- support Jens's suggestion of having the buildbot automatically assemble an "I tested this" superproject.

[1] or "head" in lowercase (thus "branch head"), but I prefer tip to avoid confusion

-- 
Thomas Rast
trast@{inf,student}.ethz.ch