Git hook to run Rubocop on changed files after committing, without locking up the terminal. Bit of a WIP.

post-commit

#!/usr/bin/env ruby

# diff-filter=AM  = only show added and modified, not removed
changed_files = `git diff-tree --no-commit-id --name-only --diff-filter=AM -r HEAD`.lines.map(&:chomp)

unless changed_files.empty?  # E.g. an "--allow-empty" commit.

  bg_process = fork do
    # This will report offenses in the entirety of the updated files, not just the changed lines. Not sure if we could easily get Rubocop to check changed-lines only, but this may be good enough.
    rubocop_results = `bundle exec rubocop --color #{changed_files.join(" ")}`

    no_offenses_detected = rubocop_results.include?("\e[32mno offenses\e[0m detected")

    unless no_offenses_detected
      puts rubocop_results
      puts
      # If the background process outputs after the prompt has rendered in the main process, you won't see a prompt with bash (maybe with zsh).
      # Could we somehow communicate back to the main process and have it display another prompt for us?
      puts "Press 'Enter' if you didn't get your prompt back."
      puts
    end
  end

  # Run in a detached BG process so the main script can finish (returning you to the terminal prompt) quickly. It can still output the results to the terminal from the BG process.
  Process.detach(bg_process)
end