prepare-deploy.rb

#! /usr/bin/env ruby

# this script takes your current commit, finds all the submodules in it, 
# makes them static files in a new tree and updates a branch called 'heroku'
# - this way you can push a project with submodules to heroku easily
# just run this, then run "git push heroku heroku:master"

current_commit = `git rev-parse HEAD`
current_tree = `git rev-parse HEAD^{tree}`
puts "Starting at tree #{current_tree}"

# get a list of submodules
status = `git submodule status`.chomp
subdata = status.split("\n")
subdata.each do |subline|
  sharaw, path = subline.split(" ")
  sha = sharaw[1, sharaw.size - 1]
  remote = path.gsub('/', '-')
  puts "Preparing #{remote} at #{sha}"
  `git remote add #{remote} #{path} 2>/dev/null` # fetch each submodule into a remote
  `git fetch #{remote}`
  `git read-tree --prefix=#{path} #{sha}` # for each submodule/sha, read-tree the sha into the path
end

# find heroku parent
prev_commit = `git rev-parse heroku 2>/dev/null`.chomp  
pcommit = (prev_commit != "heroku") ? "-p #{prev_commit}" : ''

# write-tree/commit-tree with message of what commit sha it's based on
tree_sha = `git write-tree`.chomp
commit_sha = `echo "deploy at #{current_commit}" | git commit-tree #{tree_sha} #{pcommit}`
puts "COMMIT: #{commit_sha}"

# update-ref
`git update-ref refs/heads/heroku #{commit_sha}`

# reset
`git reset HEAD`