Add a script to prohibit merge commits

Author: mame

bin/prohibit-merge-commits.rb

@@ -0,0 +1,13 @@
+#!/usr/bin/env ruby
+
+require "open3"
+
+ARGV.each_slice(3) do |oldrev, newrev, refname|
+  out, = Open3.capture2("git", "rev-list", "--parents", oldrev + ".." + newrev)
+  out.lines.each do |s|
+    if s.split.size >= 3
+      puts "A merge commit is prohibited."
+      exit 1
+    end
+  end
+end

hooks/pre-receive-pre.sh

@@ -7,4 +7,6 @@ ruby_git="/var/git/ruby.git"
 hook_log="/tmp/pre-receive-pre.log"
 ruby_commit_hook="$(cd "$(dirname $0)"; cd ..; pwd)"
 
+$ruby_commit_hook/bin/prohibit-merge-commits.rb $* || exit 1
+
 $ruby_commit_hook/bin/check-email.rb $* || exit 1