From: Thomas Rast <trast@student.ethz.ch>
Date: Wed, 13 Jan 2010 12:59:08 GMT
Subject: Re: discussion: an option to fail git fetch if a pulled branch tip is not a fast forward of the existing remote tip?
Message-ID: <201001131359.09613.trast@student.ethz.ch>
In-Reply-To: <2cfc40321001130354w626ec0fat7abdfaff9771c29f@mail.gmail.com>

Jon Seymour wrote:
[discussion of a case of branch rewriting, called "backtracking" here]
> Now clearly the upstream developer should not have backtracked. That
> said, it would have been nice if I could have easily configured my
> porcelain to detect the backtracking condition. An option on git fetch
> that implemented something similar to the git push check would have
> made this easy to achieve.

This is an instance of a non-fast-foward update, which is indicated by
the little "+" in git-fetch's output.  E.g., fetching git.git a moment
ago gave me

>From git://git.kernel.org/pub/scm/git/git
   fbb9971..8efa5f6  maint      -> origin/maint
   c0eb604..054d2fa  master     -> origin/master
   e295b7f..e84eab0  next       -> origin/next
 + 10659b7...6a048fc pu         -> origin/pu  (forced update)

which means that the 'pu' branch was a non-fast-forward update.

If you do not want to rely on checking the results manually, you can
edit the remote configuration.  Normally, it will look like

[remote "origin"]
        url = git://git.kernel.org/pub/scm/git/git.git
        fetch = +refs/heads/*:refs/remotes/origin/*

Note the "+" in the 'fetch' line, which means "allow non-fast-forward
updates".  Removing the + (leaving the rest intact) results in

>From git://git.kernel.org/pub/scm/git/git
 ! [rejected]        pu         -> origin/pu  (non-fast-forward)

You can then manually add lines _with_ the "+" for branches where you
do want to allow non-ff updates, e.g., for git.git I might say

[remote "origin"]
        url = git://git.kernel.org/pub/scm/git/git.git
        fetch = +refs/heads/pu:refs/remotes/origin/pu
        fetch = refs/heads/*:refs/remotes/origin/*

since only 'pu' will be rewritten regularly. ('next' gets the
occasional treatment too, so that config would not be very
futureproof.)

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