Proof of concept: filter a Git tree so that all files have timestamps matching the last commit to touch them

git_tree_timestamp_filter.rb

#!/usr/bin/env ruby

OUTPUT = ARGV[0]

# Convert Git timestamp into Ruby time
timestamp = Time.at(ENV['GIT_AUTHOR_DATE'].delete('@').to_i)

# Collect all real files added or modified in the commit
files = []
%x(git show --raw #{ENV['GIT_COMMIT']}).split("\n").each do |line|
  next unless /^:/.match(line)
  #$stderr.puts
  #$stderr.puts line.inspect
  (fields, file) = line.split("\t")
  fields = fields.split(/\s/)
  #$stderr.puts fields.inspect
  files << file if /^100/.match(fields[1])
end

unless files.empty?
  File.open(OUTPUT, "a") do |file|
    file.puts ["touch -c -t", timestamp.strftime("%Y%m%d%H%M.%S"), *files].join(" ")
  end
end