Re: discussion: an option to fail git fetch if a pulled branch tip is not a fast forward of the existing remote tip?

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