From: Eli Bendersky <eliben@...>
Date: 2006-05-09T05:04:35+09:00
Subject: Re: REXML exception rescuing

Eli Bendersky wrote:
>>> Thanks for your suggestion, it was clear to me that this is possible, 
>>> but I seek a more 'sane' way of doing it. What if REXML changes the 
>>> format of the message slightly in the next version - the regexes won't 
>>> match any longer. I don't see why there can't be a short way to print a 
>>> message that is useful to an end user.

Since I found no better way around it, and REXML is pretty much the only 
powerful pure-Ruby XML lib out there, I had to turn to the ugly side, 
handcrafting the sanest explanation possible out of REXML parse errors:


module REXML
  class ParseException < RuntimeError

    # Try to make the sanest possible explanation of a parse error,
    # suitable for display to users
    #
    def explain
      str = self.to_s

      # If it's the broken 'missing tag start' error,
      # output the "unconsumed chars" as they serve as
      # a good hint to the location of the problem
      #
      if str.match(/missing tag start/)
        if str.match(/Last \d+ unconsumed characters:\n([^\n]+)\n/)
          "near #{$1}"
        else
          "(unknown)"
        end
      # Otherwise it's a normal error, so return the description
      #
      else
        if str.match(/REXML::ParseException: (.*)$/)
          "#{$1}     (Line #{self.line})"
        else
          "(unknown)"
        end
      end
    end
  end
end

Tell me what you think. Could have I extracted more information ? My 
knowledge of REXML is still basic so I'm surely missing some quirks.

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