How to avoid “Merge branch 'master' of ssh

Question

Some contributors in our project likes to work on master directly and still forget to git pull --rebase.

Is there a way to refuse on the server side commit with commit like Merge branch 'master' of ... into master ?

Answer 1

As VonC comments, you can do this with a simpler version of the pre-receive hook that I wrote for that question.

To rephrase what you're asking, you would like a pre-receive hook on your server that will refuse any push to master which has any non-linear history, i.e. introduces any commit with more than one parent. This hook should do what you want:

#!/usr/bin/ruby -w

ref_to_check = "refs/heads/master"

STDIN.each_line do |line|
    rev_old, rev_new, ref = line.split(" ")

    if ref == ref_to_check
        merges_introduced = `git rev-list --merges #{rev_old}..#{rev_new}`
        unless merges_introduced.strip.empty?
            STDERR.puts "Refusing push to #{ref}, since it would create non-linear"
            STDERR.puts "history by introducing the following merge commits:"
            STDERR.puts merges_introduced
            exit(1)
        end
    end
end

Update: in Jefromi's answer to the linked question, he demonstrates that using git rev-list --merges is much neater, so I've updated this script to use that, and fixed it to loop over every ref that the push is trying to update.