git-branch-diff

#!/usr/bin/env ruby
#
# git-branch-diff
#
#   Computes the diff of the current working tree against the state
#   of the "parent" branch it was branched from.
#
# Licensed Under The BSD License
# ------------------------------
#
# Copyright (c) 2010, Scott W. Bradley <scottwb@gmail.com>
# All rights reserved.
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions are met:
#
#   * Redistributions of source code must retain the above copyright notice,
#     this list of conditions and the following disclaimer.
#
#   * Redistributions in binary form must reproduce the above copyright notice,
#     this list of conditions and the following disclaimer in the documentation
#     and/or other materials provided with the distribution.
#
#   * Neither the names Scott W. Bradley, scottwb, Strings, Inc., nor the
#     names of their contributors may be used to endorse or promote products
#     derived from this software without specific prior written permission.
#
# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
# AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
# ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
# LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
# CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
# SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
# INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
# CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
# ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
# POSSIBILITY OF SUCH DAMAGE.
#


###############################################################################
# Usage
###############################################################################
usage=<<EOT

Usage:

  git branch-diff [OPTIONS] [parent-branch]

  Computes the diff of the current working tree against the state
  of the "parent" branch it was branched from. This uses the current state
  of the working tree filesystem, assumed to be in the branch, and determines
  what changes have happened since the last merge base with the parent
  branch.

  This effectively shows you what file changes would be committed to the
  parent branch if the current working tree were to be comitted and
  merged into the parent branch.

  PARAMETERS:

    parent-branch:
      The name of the parent branch to compare to. If unspecified, this
      defaults to 'master'.

  OPTIONS:

    -h
      displays this message

  CONFIGURATION:

    You can configure the diff tool that is used to do a directory compare.
    By default it will use `diff -r`. To specify a different program by
    either using the git config, e.g.:

      git config --global branchdiff.cmd /path/to/dir/cmp/tool

    or you can set it in an environment variable, e.g.:

      export GIT_BRANCH_DIFF_CMP=/path/to/dir/cmp/tool

   If the environment variable is set, it will take precedence over
   the git config file.

EOT


###############################################################################
# Configuration
###############################################################################
DEFAULT_PARENT_BRANCH = 'master'
DEFAULT_DIR_COMPARE   = 'diff -r'


###############################################################################
# Setup
###############################################################################
require 'getoptlong'
GetoptLong.new(
  ['--help', '-h', GetoptLong::NO_ARGUMENT]
).each do |opt, arg|
  if opt == '--help'
    puts usage
    exit
  end
end


###############################################################################
# Main Program
###############################################################################

# Get the name of the parent branch and dir compare program to use.
parent_branch = ARGV[0] || DEFAULT_PARENT_BRANCH
dir_compare   = ENV['GIT_BRANCH_DIFF_CMP'] || `git config --get branchdiff.cmd`.strip
dir_compare   = DEFAULT_DIR_COMPARE if dir_compare.empty?

# Figure out the SHA of the commit that makes up the last time
# this branch was the same as the parent.
merge_base = `git merge-base #{parent_branch} HEAD`.strip

# Make a temporary directory structure "old" and "new" files
# to be dir-compared.
tmp_dir = ".git-branch-diff-tmp-%x"  % rand(2**24)
old_dir = "#{tmp_dir}/old"
new_dir = "#{tmp_dir}/new"
system("mkdir #{tmp_dir}")
system("mkdir #{old_dir}")
system("mkdir #{new_dir}")

# Find all the file that are different and copy the old and new versions
# into the old and new directories to be compared.
`git diff --name-status #{merge_base}`.each_line do |line|
  line.strip!
  if line =~ /^([^\s]+)\s+(.+)$/
    status   = $1
    filename = $2
    subdir   = File.dirname(filename)
    system("mkdir -p \"#{old_dir}/#{subdir}\"")
    system("mkdir -p \"#{new_dir}/#{subdir}\"")

    # If it's not a new file, grab a copy of the old one.
    if status != 'A'
      system("git show \"#{merge_base}:#{filename}\" > \"#{old_dir}/#{filename}\"")
    end

    # If it's not a deleted file, grab a copy of the current one.
    if status != 'D'
      system("cp \"#{filename}\" \"#{new_dir}/#{filename}\"")
    end
  end
end

# Run the directory compare on the temporary old and new dirs.
system("#{dir_compare} \"#{old_dir}\" \"#{new_dir}\"")

# Cleanup tmp dirs.
system("rm -rf \"#{tmp_dir}\"")