A Git hook for prepending commit messages with an issue number found in the current working branch. It's organized for use with the https://github.com/icefox/git-hooks project for managing git hooks.

issue_numbers.rb

#! /usr/bin/env ruby

# ~/.git_hooks/lib/issue_numbers.rb

$issue_pattern = /\d{5}(?=-)/

#require 'git'

#g = Git.open(working_dir, :log => Logger.new(STDOUT))

# TODO: Break out separate Branch class
class Commit
  attr_accessor :git_root, :merge_branch, :current_branch,
                :current_issue

  def initialize
    @related_issues = []

    # Determine relevant git directories
    @git_root = %x{git rev-parse --show-toplevel}.chomp
    @git_dir = "#{@git_root}/.git"

    # Examine current branches
    @current_branch = get_branch_name(%x{git symbolic-ref HEAD})
    @current_issue = Commit.parse_issue_number(@current_branch)
    add_related_issue(@current_issue) unless @current_issue.nil?

    if is_merge?
      @merge_branch = parse_merge_branch
      @merge_issue = Commit.parse_issue_number(@merge_branch)
      add_related_issue(@merge_issue) unless @merge_issue.nil?
    end
  end

  def self.parse_issue_number(str)
    match = $issue_pattern.match(str)
    unless match.nil?
      match.to_s
    end
  end

  def add_related_issue(issue)
    @related_issues << issue
  end

  # TODO: Resolve why this isn't picking up the initial merge state
  def is_merge?
    File.exists? "#{@git_dir}/MERGE_HEAD" 
  end

  def parse_merge_branch
    merge_hash = %x{cat '#{@git_dir}/MERGE_HEAD'}
    get_branch_name(merge_hash)
  end

  def get_branch_name(hash)
    ref = %x{git describe --all --exact-match #{hash}}.chomp
    if $?
      return ref.gsub('heads/', '')
    else
      return nil
    end
  end

  def commit_prefix
    prefix = ""
    @related_issues.each do |issue|
      prefix << "[##{issue}]"
    end

    prefix << ' ' unless @related_issues.empty?
  end
end

prepend-issue-number

#! /usr/bin/env ruby

# ~/.git_hooks/prepare-commit-msg/prepend-issue-number


# --------------------------------------------------------------------------------
# Git hook script to search merge commits for possible issue numbers and prepend them
# in a standardized flag at the beginning of the commit message.
#
# Currently the script only searches for 5 digit number sequences and prepends those
# to the commit message on the assumption it's the branch number. In the case of most
# merges this issue number is expected to come from the branch name being merged.
# --------------------------------------------------------------------------------

require_relative '../lib/issue_numbers.rb'
require 'tempfile'

# Return description of the task if --about flag is provided.
if ARGV[0] == '--about' then
  puts "Insert the issue number in the merge commit message if available in branch name."
  exit
end

msg_file = ARGV[0]
commit_type = ARGV[1]

# TODO: Check for pre-existing issue tags
def prepend_issue_prefix(prefix, msg_file)
  # Compile full commit message in a temporary file to avoid
  # potential memory leaks from loading a large file into memory
  temp = Tempfile.open('tmp_msg') { |tf|
    # Print prefix at the beginning
    tf.print(prefix);

    # Read and merge the existing file
    tf.print(File.read(msg_file));

    # Return the temp file for the move step
    tf
  }

  # Replace the original file with the newly merged file
  FileUtils.move(temp.path(), msg_file)
end

# Parse the issue number from the branch name in the default commit message
def fetch_commit_msg(msg_file)
  File.open(msg_file) do |handle|
    msg = handle.readline

    Commit.parse_issue_number(msg)
  end
end

c = Commit.new

# Special handling for merges
if commit_type == 'merge'
  # We only need special handling if the lib isn't picking it up
  unless c.is_merge?
    issue = fetch_commit_msg(msg_file)
    c.add_related_issue(issue) unless issue.nil?
  end
end

prefix = c.commit_prefix
unless prefix.nil? || prefix.empty?
  prepend_issue_prefix(prefix, msg_file)
end