Bug #73762 [Com]: recursive pattern breaks from pcre 8.36 to 8.37

Edit report at https://bugs.php.net/bug.php?id=73762&edit=1 ID: 73762 Comment by: zhihong dot chen dot cn at gmail dot com Reported by: zhihong dot chen dot cn at gmail dot com Summary: recursive pattern breaks from pcre 8.36 to 8.37 Status: Not a bug Type: Bug Package: PCRE related Operating System: Ubuntu 14.04.5 X64 PHP Version: 5.6.9 Block user comment: N Private report: N New Comment: Many thanks. It's my pattern's problem. This bug could be identified as Invalid. Previous Comments: ------------------------------------------------------------------------ [2016-12-17 05:13:51] requinix@php.net This would be a behavioral change in pcrelib, not in PHP. Looking through the changelog, nothing stands out as a change that would obviously impact your regex. However #11 seems at least partially relevant: >11. If an assertion that was used as a condition was quantified with a minimum > of zero, matching went wrong. In particular, if the whole group had > unlimited repetition and could match an empty string, a segfault was > likely. The pattern (?(?=0)?)+ is an example that caused this. Perl allows > assertions to be quantified, but not if they are being used as conditions, > so the above pattern is faulted by Perl. PCRE has now been changed so that > it also rejects such patterns. http://www.pcre.org/original/changelog.txt Fixing that may have exposed the problem with your regex: #\{(?:(?<name>\w+))(?:/\}|\}(?<snippet>(?:[^{]*|(?!\{\w+:\})++|(?R))*+)\{end\})#mu ^1 ^2 1. A quantifier on an assertion doesn't make sense, even if it is allowed. Apparently Perl allows it so pcrelib does too. This is minor and doesn't affect the matching. 2. The possessive quantifier does affect the matching. The snippet portion will match the space after {first} but not attempt the rest of the snippet pattern, then stop when {end} fails to match, and the engine backtracks until it eventually resumes matching at {second}. If I change the regex to #\{(?:(?<name>\w+))(?:/\}|\}(?<snippet>(?:[^{]*|(?!\{\w+:\})|(?R))*)\{end\})#mu ^ ^ then I get the expected results in all versions of PHP. https://3v4l.org/2BrI6 ------------------------------------------------------------------------ [2016-12-16 16:51:58] zhihong dot chen dot cn at gmail dot com Description: ------------ From php 5.6.9 after pcre upgrade to 8.37 and later. Recursive matching breaks. generate different result. when using php 5.6.8 and before version Will generate expect result. Later version will generate incorrect result. Test script: --------------- <?PHP const pattern = "#\{(?:(?<name>\w+))(?:/\}|\}(?<snippet>(?:[^{]*|(?!\{\w+:\})++|(?R))*+)\{end\})#mu"; $ss = <<<'EOD' {first} {second}within second{end} {end} EOD; function testRun($input ){ echo $input[0]; echo PHP_EOL; } preg_replace_callback( pattern ,'testRun',$ss); Expected result: ---------------- {first} {second}within second{end} {end} Actual result: -------------- {second}within second{end} ------------------------------------------------------------------------ -- Edit this bug report at https://bugs.php.net/bug.php?id=73762&edit=1