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

I spent a little while this afternoon debugging an issue where an upstream publisher had backtracked and published a branch tip which was not a descendant of a previously published (and fetched) branch tip. The net result was that the backtracked changes were preserved in the downstream branch once the 2nd tip was pulled.

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.

Has any consideration been given to such an option? Is there a well-known alternative pattern for detecting this case?

jon.

Jon Seymour wrote: [discussion of a case of branch rewriting, called "backtracking" here]

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

   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

 ! [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,

Ah - thanks for your very helpful response!

jon.

On 13/01/2010, at 23:59, Thomas Rast <trast@student.ethz.ch> wrote: