commit-msg hook to add a prefix to commit messages

commit-msg

#!/usr/bin/env ruby
#
# Git commit-msg hook. If your branch name is in the form "US1234-postfix", or
# "US1234_postfix", it automatically adds the prefix "[US1234]" to commit
# messages.
#
# Example
# =======
#
#    git checkout -b US1234-some-cool-feature
#    git commit "new stuff"
#    git log    => will show up "[US1234] new stuff"
#
# If you include "#noref" in the commit message, nothing will be added to the
# commit message, and the "#noref" itself will be stripped.
#
# Example
# =======
#
#    git commit "don't prefix this message #noref"
#    git log    => will show up "don't prefix this message"
#
# Install
# =======
#
#   cd your_project
#   curl https://raw.github.com/gist/2926764/7b61cd1f2f1f399492182ed4b5dbabca3f96cced/commit-msg > your_project/.git/hooks
#   chmod +x .git/hooks/commit-msg
#
# Testing
# =======
#
# git init a new repo, install the commit hook, and run:
#
#   ruby .git/hooks/commit-msg testing
#
# --
# E. Oga, adapted from https://gist.github.com/184711 By Henrik Nyh
# <http://henrik.nyh.se> 2009-09-10 under the MIT License.

# Convert a message to include branch name information.
class Transmogrifier < Struct.new(:message, :branchname)
  NOREF_MATCHER  = /#noref/
  PREFIX_MATCHER = /\A(\w{1,2}\d{4,5})[-_]/
  PREFIX_FORMAT = "[%s] %s"

  def prefix
    (branchname.to_s[PREFIX_MATCHER, 1] || "").strip
  end

  def to_s
    return message unless prefix =~ /\S/

    if message =~ NOREF_MATCHER
      output = message.gsub(NOREF_MATCHER, "")

    elsif message.include?(prefix)
      output = message

    else
      output = PREFIX_FORMAT % [prefix, message]
    end

    output.squeeze(" ").strip
  end
end

# Overwrites the file which holds the commit message with a fancier one.
def run!
  branchname   = `git branch --no-color 2> /dev/null`[/^\* (.+)/, 1].to_s
  message_path = ARGV.first
  message      = File.read(message_path).strip.chomp

  File.open(message_path, 'w') {|f| f.write Transmogrifier.new(message, branchname) }
end

if ARGV.first != "testing"
  run!

else
  ################################################################################
  # TESTS
  ################################################################################

  puts "This will commit stuff to your repo! Do you want to proceed? [yes/n]: "
  abort unless $stdin.gets.chomp.downcase == "yes"

  require 'shellwords'

  def change_branch(name)
    `git checkout -B #{name}`
  end

  def commit(msg)
    `echo 'testing' >> a; git add a; git commit -m #{msg.shellescape}`
  end

  def top_message
    `git log --format="%s" -n1`.chomp
  end

  def assert_equal(a, b)
    abort "\nFailure!\n#{a.inspect} != #{b.inspect}\n#{caller.join("\n")}" unless a == b
  end

  def commit_and_check(msg, expected_message)
    commit(msg); assert_equal(top_message, expected_message)
  end

  change_branch "US1234_some_cool_feature"
  commit_and_check "new stuff"                 , "[US1234] new stuff"
  commit_and_check "[US1234] new stuff"        , "[US1234] new stuff"
  commit_and_check "don't mess with me #noref" , "don't mess with me"

  change_branch "US1234-some-cool-feature"
  commit_and_check "new stuff"                 , "[US1234] new stuff"
  commit_and_check "[US1234] new stuff"        , "[US1234] new stuff"
  commit_and_check "don't mess with me #noref" , "don't mess with me"

  change_branch "some-feature-without-a-task"
  commit_and_check "does not change the message"          , "does not change the message"
  commit_and_check "[US1234] does not change the message" , "[US1234] does not change the message"
  commit_and_check "it doesn't remove the #noref"         , "it doesn't remove the #noref"

  change_branch "master"
  commit_and_check "does not change the message"          , "does not change the message"
  commit_and_check "[US1234] does not change the message" , "[US1234] does not change the message"
  commit_and_check "it doesn't remove the #noref"         , "it doesn't remove the #noref"

  puts "\nAll tests passed."
end