Monkey patch Psych string to date parsing for non-date strings

psych_date_parsing_patch.rb

require 'psych'

# NOTE(chrislwade): See https://github.com/tenderlove/psych/issues/42 for more details.

# Monkey patch to deal with strings that look like dates but aren't really
# dates.  The example encountered within our context is product codes in the
# form of ####-##-## which looks like a date on the surface but is really a
# good old string.  This patch simply aims to replace the buggy version of
# "date" handling with one that behaves like the new implementation in Psych
# while leaving the remaining functionality of the existing Psych version
# alone.

# Only load the patch when using a buggy version of psych.
has_buggy_psych = begin
  YAML.dump('5555-55-55')
  $stderr.puts "Psych is working properly! (Please remove me #{__FILE__}.)"
  false
rescue ArgumentError
  $stderr.puts 'Psych is mis-behaving!'
  true
end

if has_buggy_psych
  $stderr.puts 'Teaching Psych how to behave!'
  class Psych::ScalarScanner
    alias :tokenize_with_date_parsing_bug :tokenize

    def tokenize(string)
      return nil if string.empty?
      return string if @string_cache.key?(string)

      case string
      when /^\d{4}-\d{1,2}-\d{1,2}$/
        require 'date'
        begin
          Date.strptime(string, '%Y-%m-%d')
        rescue ArgumentError
          string
        end
      else
        tokenize_with_date_parsing_bug(string)
      end
    end
  end
end

Updated to only monkey-patch buggy versions of psych.