Rails assets compilation using the correct RAILS_ENV into a Git branch

compile.rb

#!/usr/bin/env ruby

##
# Compile script for Rails assets that puts the assets into their [environment] branch
# thus not polluting the master branch with the files in public/assets that only
# apply to that environment.  See https://github.com/rails/sass-rails/issues/93#issuecomment-3982582
#
# Usage: ./compile [environment]

# supported environments
ENVIRONMENTS = ['ci','staging','production']

if ARGV.length == 0
  puts "Error: Usage: compile [environment]"
  exit false
elsif (!ENVIRONMENTS.include?(ARGV[0]))
  puts "Error: Environment '#{ARGV[0]}' is not valid.  Please use: #{ENVIRONMENTS.join(', ')}"
  exit false
else
  environment = ARGV[0]
  ENV['RAILS_ENV'] = environment

  branch_list = %x[git branch]
  branches = branch_list.gsub(/\*\s/, '').split(/[\n\r]/).map { |d| d.strip }
  current_branch = branch_list.match(/\*\s(.*)/)

  if !current_branch || current_branch[1] == '(no branch)'
    puts "Error: Current branch not selected.  You must have a branch selected before compiling assets."
    exit false
  else
    current_branch = current_branch[1]
  end

  if current_branch != environment
    puts "--- Current branch #{current_branch}, saving current changes ---"
    if branches.include?(environment)
      unless system("git branch -D #{environment}")
        puts "Error: Branch could not be deleted"
        exit false
      end
    end

    unless system('git stash save "changes from before compile run"') && system("git checkout -b #{environment}")
      puts "Error: Unable to stash and checkout new branch #{environment}."
      puts "You may need to git stash pop."
      exit false
    end
  else
    puts "\n--- Already on branch #{environment} ---"
  end

  puts "\n--- Compiling assets for #{environment}---"
  unless system 'bundle exec rake assets:precompile'
    puts "Error: Compilation failed"
    exit false
  end

  puts "\n--- Committing ---"
  asset_path = File.join(File.dirname(__FILE__), '../public/assets')
  branch_specified = current_branch != environment ? " from branch #{current_branch}" : ' (original branch unknown)'
  unless system("git add #{asset_path}/*") && system("git commit -m \"Assets compiled and added#{branch_specified}\"")
    puts "Error: Could not commit assets to repository"
    exit false
  end

  if current_branch != environment
    puts "\n--- Reverting back to branch #{current_branch} and cleaning up assets ---"
    unless system("git checkout #{current_branch}")
      puts "Error: Could not revert back to branch #{current_branch} and retrieve your local changes from the stash."
      puts "Check your local branch and working files.  If files or changes are missing check `git stash list`"
      puts "Finally ensure no residual asset files exist in #{asset_path}"
      exit false
    end

    unless system("rm -fr public/assets")
      puts "Error: Could not delete residual asset files from #{asset_path}"
      puts "If files or changes are missing check `git stash list`"
      puts "Finally ensure no residual asset files exist in #{asset_path}"
    end

    stashes = %x[git stash list]
    this_stash = stashes.match(/^(stash@\{\d+\}):.*changes from before compile run$/m)
    if this_stash
      puts "\n--- Retrieving changes from stash ---"
      unless system("git stash pop #{this_stash[1]}")
        puts "Error: Could not retrieve your local changes from the stash."
        puts "If files or changes are missing check `git stash list`"
        exit false
      end
    end
  end

  puts "\n--- Compile done ---"
end

deploy.rb

#!/usr/bin/env ruby

##
# Deployment script for Heroku that pushes an [environment] branch
# to that environment target in git
# For example, if you have set up a remote called staging, and a branch named staging
# then you can deploy to the remote staging by executing
# ./deploy staging
# which simply does: git push staging staging:master

require 'optparse'

# supported environments
ENVIRONMENTS = ['ci','staging','production']

options = {}

optparse = OptionParser.new do |opts|
  # Set a banner, displayed at the top
  # of the help screen.
  opts.banner = "Usage: deploy [environment] [--rebase]"

  options[:rebase] = false
  opts.on('-r', '--rebase', 'Rebase the environment branch onto the current branch (use when assets have not changed but repository has)') do
    options[:rebase] = true
  end

  options[:compile] = false
  opts.on('-c', '--compile', 'Compile the assets first using compile script)') do
    options[:compile] = true
  end

  opts.on('-h', '--help', 'Display this help screen') do
    puts opts
    exit
  end

  if ARGV.length == 0
    puts opts
    exit false
  end
end.parse!

environment = ARGV.first
if (!ENVIRONMENTS.include?(environment))
  puts "Error: Environment '#{environment}' is not valid.  Please use: #{ENVIRONMENTS.join(', ')}"
  exit false
else
  if options[:compile]
    compile_path = File.join(File.dirname(__FILE__), '../script')
    unless system("#{compile_path}/compile #{environment}")
      puts "Error: Unable to pre-compile assets for environment #{environment} so aborting."
      exit false
    end
  end

  current_branch = %x[git branch].match(/\*\s(.*)/)

  # rebase the environment branch onto the current branch and then deploy
  if options[:rebase]
    if current_branch
      current_branch = current_branch[1]
    else
      puts "Error: You are not on a current rebranch so we cannot rebase"
      exit false
    end

    if current_branch == environment
      puts "Error: Cannot rebase #{environment} onto #{current_branch} as already on #{current_branch} branch"
      exit false
    end

    unless system('git stash save "changes from before deploy"') && system("git checkout #{environment}")
      puts "Error: Unable to stash and checkout branch #{environment}."
      puts "It is possible that you have changes in a stash now.  Use git stash list & git stash pop."
      exit false
    end

    unless system("git rebase #{current_branch}")
      puts "Error: Could not rebase #{environment} onto #{current_branch}."
      puts "It is likely that you have changes in a stash now.  Use git stash list & git stash pop."
      exit false
    end

    unless system("git checkout #{current_branch}")
      puts "Error: Could not revert back to branch #{current_branch}"
      puts "It is likely that you have changes in a stash now.  Use git stash list & git stash pop."
      exit false
    end

    stashes = %x[git stash list]
    this_stash = stashes.match(/^(stash@\{\d+\}):.*changes from before deploy$/m)
    if this_stash
      unless system("git stash pop #{this_stash[1]}")
        puts "Error: Could not retrieve your local changes from the stash."
        puts "If files or changes are missing check `git stash list`"
        exit false
      end
    end
  end

  remotes = %x[git remote].split(/[\n\r]/).map { |d| d.strip }

  if !remotes.include?(environment)
    puts "Error: You must have Git set up with the remote #{environment} pointing to the relevant Heroku environment repository"
    puts "Example: git remote add staging [email protected]:staging-yourapp.git"
    exit false
  end

  puts "--- Pushing application with assets for '#{environment}' to Heroku ---"
  unless system "git push #{environment} #{environment}:master --force"
    puts "Error: Unable to push changes to Heroku"
    exit false
  end
end

Please note that both compile.rb & deploy.rb should be named compile and deploy and should have chmod 775 set on them