Clean Git Branches

clean-git.rb

# @author jmnsf
#
# This script attempts to clean the local repository of stale branches. This
# goes in a few steps:
#
# 0. Fetch with `-p` is run to remove references to deleted remote branches.
# 1. Merged branches are removed (except for `master`).
# 2. Branches with no conflicts or changes vs `master` are removed.
# 3. Branches that have the same head as a merged PR in GitHub will be merged.
#
# Typically 0 and 1 would suffice, but with Squash & Merge local branches never
# get "merged" to master, so git doesn't know they can be removed. During step
# 3 force deletion is run with a prompt each time.

require 'excon'
require 'json'

# Simple API wrapper
class GitHub
  def initialize(username, password, organization, repository)
    @org = organization
    @repo = repository
    @connection = Excon.new(
      'https://api.github.com',
      user: username, password: password, persistent: true
    )
  end

  # Grabs a branch's closed Pull Requests from GitHub.
  #
  # @param  branch  [String] The name of the branch to get pulls from.
  # @return         [Array]  An array of closed pull requests with the branch as
  #                          HEAD.
  def fetch_pulls(branch)
    res = get "/repos/#{@org}/#{@repo}/pulls?state=closed&head=#{@org}:#{branch}"

    raise 'Bad credentials' if res.status == 401

    JSON.parse res.body
  end

  private

  # Make a GET request to some path in GH. If the socket is closed, tries once
  # more.
  #
  # @param  path  [String]   The path to GET.
  # @param  tried [Boolean]  Whether it's been tried.
  # @return       [Response] The Response object from Excon
  def get(path, tried: false)
    @connection.get path: path
  rescue Excon::Errors::SocketError
    # Excon fails with socket-error instead of reviving the connection so it
    # needs a manual retry
    fail err if tried
    return get path, tried: true
  end
end

def clean_all_merged
  `git branch --merged | grep -P '^(?![\\* ] master)' | xargs git branch -d`
end

# Checks if a branch has conflicts with `master`.
#
# @param  branch [String] Name of the branch to check for conflicts
# @return [Boolean]       Whether it's got conflicts
def has_conflicts? branch
  merge_base = /\w+/.match `git merge-base master #{branch}`
  merge_tree = `git merge-tree #{merge_base} master #{branch}`

  />>>>>/ =~ merge_tree
end

# Attempts to rebase a branch onto `master` and then remove it safely (`-d`).
# Returns true or false whether that was possible.
#
# @param  branch [String] Name of the branch to check for conflicts.
# @return [Boolean]       Whether the branch was removed successfully.
def rebase_and_remove branch
  `git checkout #{branch} -q`

  if system 'git rebase master -q'
    `git checkout master -q`
    return system "git branch -d #{branch} -q"
  else
    puts "Could not rebase #{branch}. Aborting."
    `git rebase --abort`
    `git checkout master -q`
    return false
  end
end

# Check `branch` for conflicts with master. If none exist, try rebasing onto
# master and removing safely.
#
# @param  branch [String]  The name of the merged branch to be removed.
# @return        [Boolean] Whether the branch was removed.
def try_safe_removal branch
  return false if has_conflicts? branch
  rebase_and_remove branch
end

# Confirm branch removal with user and enforce it if allowed.
#
# @param  pull   [Object]  The pull request object that merged the branch.
# @param  branch [String]  The name of the merged branch to be removed.
# @return        [Boolean] Whether the branch was removed.
def prompt_force_remove pull, branch
  puts "Head of '#{branch}' was merged in PR ##{pull['number']} - #{pull['title']}"
  puts "Force remove it? [Y/n]"
  answer = gets.chomp.downcase

  return false if answer == 'n'
  return `git branch -D #{branch}` if answer == '' || answer == 'y'

  puts "Please answer 'y' or 'n'."
  force_remove pull, branch
end

`git fetch --all -p -q`
`git checkout master -q`

clean_all_merged

local_branches = `git branch | cut -c 3- | grep -v master`.split("\n")
remote_branches = `git branch -r | cut -c 3-`.split("\n")

puts "Found #{local_branches.length} local branches and " +
  "#{remote_branches.length} remotes."

non_remote_locals = local_branches.reject do |branch|
  remote_branches.any? { |rb| rb.end_with? branch }
end

puts "#{local_branches.length - non_remote_locals.length} branches have live " \
  'remotes and will be skipped.'

conflict_branches = local_branches.reject { |branch| try_safe_removal branch }

exit puts('All done.') if conflict_branches.length.zero?

# Some branches weren't safe for removal. Lets try GitHub
puts "#{conflict_branches.length} branches remain with conflicts. Trying GitHub."

_, org, repo = (/origin\s.+[\/:](.+)\/(.+)\.git/.match `git remote -v`).to_a

puts "Connecting to #{org}/#{repo}..."

username = `git config --get github.user`.chomp

if username.empty?
  puts "What's your username?"
  username = gets.chomp
end

puts "What's your password?"
system 'stty -echo'
password = gets.chomp
system 'stty echo'

gh = GitHub.new(username, password, org, repo)

not_deleted = conflict_branches.reject do |branch|
  branch_sha = `git rev-parse #{branch}`.chomp
  pulls = gh.fetch_pulls branch

  pulls.delete_if do |pull|
    pull['merged_at'].nil? || pull['head']['sha'] != branch_sha
  end

  if pulls.length == 0
    puts "No merged PR was found for #{branch}, skipping."
    next false
  end

  prompt_force_remove pulls[0], branch
end

puts 'Done. Branches that were not deleted:'
not_deleted.each { |branch| puts branch }