Automatic Gemfile version specifier

gemfile_version_specifier.rb

# Run `ruby gemfile_version_specifier.rb` in project root directory.

require 'astrolabe/builder'
require 'parser/current'
require 'bundler'

source_buffer = Parser::Source::Buffer.new('Gemfile')
source_buffer.read

builder = Astrolabe::Builder.new
parser = Parser::CurrentRuby.new(builder)

root_node = parser.parse(source_buffer)
rewriter = Parser::Source::Rewriter.new(source_buffer)

gem_nodes_without_version_specification = root_node.each_node(:send).select do |send_node|
  _receiver, message, gem_name_node, version_node, = *send_node
  next false unless message == :gem
  next false unless gem_name_node.str_type?
  version_node.nil?
end

gem_specs = Bundler::LockfileParser.new(File.read('Gemfile.lock')).specs

gem_nodes_without_version_specification.each do |send_node|
  _receiver, _message, gem_name_node, = *send_node
  gem_name, = *gem_name_node

  gem_spec = gem_specs.find { |spec| spec.name == gem_name }
  version_specification = '~> ' + gem_spec.version.to_s.split('.')[0, 2].join('.')
  rewriter.insert_after(gem_name_node.loc.expression, ", '#{version_specification}'")
end

rewrittern_source = rewriter.process
File.write('Gemfile', rewrittern_source)