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Can't ENCLOSE_OPTION be allowed in look-behind? #17

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merged 1 commit into from May 29, 2013
Merged

Can't ENCLOSE_OPTION be allowed in look-behind? #17

merged 1 commit into from May 29, 2013

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knu
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@knu knu commented May 27, 2013

Currently Onigmo (or Oniguruma) does not allow option enclosures (like (?i)) in look-behind, but isn't it possible to allow them?

Taking Ruby as example, this restriction prevents a pattern from being interpolated within a look-behind construct of another.

pattern1 = /foo/  # stringified as "(?-mix:foo)"
pattern2 = /(?<=#{pattern1})/
#=> RegexpError: invalid pattern in look-behind: /(?<=(?-mix:foo))/

This pull request is an unconfirmed attempt to fix the problem.
Thanks for your consideration.

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knu commented May 28, 2013

On second thought, (?i) may lead a subpattern to variable-length in Unicode case fold semantics. Is that right?
Is there any other option that affects a pattern length? We need to case out those if that is the case.

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knu commented May 28, 2013

It doesn't seem like it. In Onigmo/Oniguruma, look-behind does not take Unicode case-folding into account in the first place.

Below is taken from an irb session on ruby 2.0.

>> /(?:\u{149})a/ui =~ "[\u{2bc}na]"  # Unicode case-folding match is in effect.
=> 1
>> /(?<=\u{149})a/ui =~ "[\u{2bc}na]"  # But look-behind does not take account of it.
=> nil

This looks like a bug.

k-takata added a commit that referenced this pull request May 29, 2013
@k-takata
[dist] update testpy.py
b1df572 
Add tests for the Issue #17.
k-takata added a commit that referenced this pull request May 29, 2013
@k-takata
Merge pull request #17 from knu/allow_options_in_lb
96c0be8 
Can't ENCLOSE_OPTION be allowed in look-behind?
@k-takata k-takata merged commit 36102fb into k-takata:master May 29, 2013
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Thank you for the pull request. I also added tests for this.

@k-takata k-takata mentioned this pull request May 29, 2013
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HonoreDB pushed a commit to HonoreDB/ruby that referenced this pull request Nov 12, 2013
@knu
* test/ruby/test_regexp.rb
a62ee36 
  (TestRegexp#test_options_in_look_behind)
  (TestRegexp#assert_match_at): Add tests for another problem
  fixed in Onigmo 5.13.5.  Previously Onigmo did not allow option
  enclosures in look-behind, which makes it impossible to
  interpolate a regexp into another in the middle of a look-behind
  pattern.  cf. k-takata/Onigmo#17

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@41792 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
tenderlove pushed a commit to tenderlove/ruby that referenced this pull request Jan 24, 2014
@knu
* test/ruby/test_regexp.rb
1837530 
  (TestRegexp#test_options_in_look_behind)
  (TestRegexp#assert_match_at): Add tests for another problem
  fixed in Onigmo 5.13.5.  Previously Onigmo did not allow option
  enclosures in look-behind, which makes it impossible to
  interpolate a regexp into another in the middle of a look-behind
  pattern.  cf. k-takata/Onigmo#17

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@41792 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
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