A pre-commit git hook heavily inspired from https://github.com/ashfurrow/danger-swiftlint/

pre-commit.rb

#!/usr/bin/env ruby

require 'json'

def puts_violation(violation)
  severity  = violation['severity']
  filename  = violation['file'].split('/').last
  line      = violation['line']
  reason    = violation['reason']
  
  puts "#{severity} : #{filename}, line #{line}, #{reason}"
end

config_file = File.file?('./.swiftlint.yml') ? './.swiftlint.yml' : nil
swift_files = `git diff --cached --name-only --diff-filter=AMC | grep "\.swift$"`.lines

swiftlint_command = "swiftlint lint --quiet --reporter json"
swiftlint_command += " --config #{config_file}" if config_file

result_json = swift_files.uniq.collect { |f| JSON.parse(`#{swiftlint_command} --path #{f}`.strip).flatten }.flatten
warnings    = result_json.select { |results| results['severity'] == 'Warning' }
errors      = result_json.select { |results| results['severity'] == 'Error' }

warnings.each { |violation| puts_violation violation }
errors.each   { |violation| puts_violation violation }

exit errors.count