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[Help-source-highlight] Re: Backreferences in source-highlight 2.7

From: gnombat
Subject: [Help-source-highlight] Re: Backreferences in source-highlight 2.7
Date: Sun, 10 Jun 2007 16:33:57 -0500
User-agent: Thunderbird (X11/20070604)

Lorenzo Bettini wrote:
gnombat wrote:
I'm having trouble with backreferences in source-highlight 2.7.  If I
create a language definition file named foo.lang:

keyword = `a(.)\1`

And then I create a test file

aaa abb acc a** a@@

And then I run source-highlight:

source-highlight --lang-def=foo.lang

Then "aaa", "abb" and "acc" are highlighted, but "a**" and "a@@" are
not.  Shouldn't the dot match any character?

yes you're right, so this must be a bug...

I'll try to work on it tomorrow

thanks for the feedback!

I think I figured out what is going on: is_to_isolate from regexpstatebuilder.cpp is treating the regular expression as an alphanumerical string because `a(.)\1` starts and ends with a letter or number.

 * An expression is isolated basically if it is an alphanumerical
 * string
 * TODO check whether this is actually correct in principle
 * @param s
 * @return
bool is_to_isolate(const string &s) {
  if (s.size()) {
if ((isalnum(s[0]) || s[0] == '_') && (isalnum(s[s.size()-1]) || s[s.size()-1] == '_'))
      return true;

  return false;

Then the whole regular expression gets surrounded with word boundary characters. This causes the match to fail with "a**" and "a@@".

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