Npp v8.7.8 or later hangs for `^.{0,20}` at the end of a file

mkupper

In this forum thread @coises had posted a regexp that included {0,4000}

I wondered if the zero was needed and so tested marking with ^.{,20} to see the first 20 characters of each line highlighted. Notepad reported Find: Can't find the text "^.{,20}" in entire file. That was a bit curious as I’m not sure what the engine was trying to match.

I then tried ^.{1,20} and it marks the first 20 characters for all lines that are 1 to 20 or more characters long.

Next I tried ^.{0,20} This works much like ^.{1,20} and also reports ^ zero length match on the empty lines as expected. However, when it was at the end of the file Notepad++ hangs rather than wrapping to the start of the file.

^.{0,20} works and wraps at the end of a file for npp v8.7.7.
^.{0,20} works but hangs at the end of a file for npp v8.7.8 and v8.7.9.

Before posting a bug report I’m wondering if there is something else we could try that seems useful.

Coises

@mkupper
Sounds like this:

https://github.com/notepad-plus-plus/notepad-plus-plus/pull/16371

which was accepted but is not yet in a release.

Coises

@mkupper said in Npp v8.7.8 or later hangs for `^.{0,20}` at the end of a file:

Notepad reported Find: Can’t find the text “^.{,20}” in entire file. That was a bit curious as I’m not sure what the engine was trying to match.

Per Boost documentation:

Note that the “{” and “}” characters will treated as ordinary literals when used in a context that is not a repeat: this matches Perl 5.x behavior.

Leading comma within curly braces is not a valid syntax, so it’s searching for the beginning of a line followed by any one character and then the literal characters {,20}.

Coises

@mkupper See also:
https://community.notepad-plus-plus.org/topic/26737/notepad-release-8-7-9/2?_=1744230923582
and following comments.

mpheath

@Coises said in Npp v8.7.8 or later hangs for `^.{0,20}` at the end of a file:

Leading comma within curly braces is not a valid syntax, so it’s searching for the beginning of a line followed by any one character and then the literal characters {,20}.

Python’s re allows that syntax of omitting the minimum repetition. To use {,20} instead of {0,20} would be like learning a bad habit compared to Boost or other regex libraries.

https://www.pcre.org/original/doc/html/pcrepattern.html quote:

An opening curly bracket that appears in a position where a quantifier is not allowed, or one that does not match the syntax of a quantifier, is taken as a literal character. For example, {,6} is not a quantifier, but a literal string of four characters.

This is stated explicitly that {,6} is a “literal string”.