From: naruse@...
Date: 2016-09-30T21:57:54+00:00
Subject: [ruby-core:77463] [Ruby trunk Bug#12728][Rejected] Negative lookahead does not work for "+" even though works for "@"

Issue #12728 has been updated by Yui NARUSE.

Status changed from Open to Rejected

In case 2, the regexp just behave as if

```
t %r{
    (?<!\\)\(                           # outer bracket
    o\+

    (?<!\\) ([+*]|\{\d+,\}) (?!\+)  # inner repetition, non possessive

    .*
    (?<!\\)\)                           # outer bracket
    (?<!\\) (?:[+*]|\{\d+,\}) # unbounded repetition, non possessive

  }x, "f(o++)+"
```

Of course it matches.
Maybe use should `[a-zA-Z0-9]*` or something instead of `.*`.

----------------------------------------
Bug #12728: Negative lookahead does not work for "+" even though works for "@"
https://bugs.ruby-lang.org/issues/12728#change-60734

* Author: Robert Klemme
* Status: Rejected
* Priority: Normal
* Assignee: 
* ruby -v: ruby 2.2.5p319 (2016-04-26 revision 54774) [x86_64-cygwin]
* Backport: 2.1: UNKNOWN, 2.2: UNKNOWN, 2.3: UNKNOWN
----------------------------------------
I'll attach a test program that shows the effect.  Basically, if I have a negative lookahead in the regex like (?!@) and "@" shows up in the proper location I get a mismatch (1. case).  This is expected.  If I exchange the "@" with a "\+" or "[+]" in the regex and a "+" in the input, a match occurs (case 2 and 3).  This is the bug.  If the "+" or "@" is removed from the string an expected match occurs (case 4 and 5).  I was not able to boil this down to a smaller example yet.

---Files--------------------------------
rx-mini.rb (1.63 KB)


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