I am using the following regex in vscode for a search and replace. It is to match an outer tag with plus 3 nested tags.
<tag>(((.|\n)*?)(</tag>)){4}
If i add any character to the end of this regex, vscode crashes. In my case i was going to specify a tag after that match.
Im pretty new to regex so trying to keep it simple.
I know this is a common problem and something to do with backtracking and i want to know how to simply this.
NEVER use (.|\n)*?. It is a very misfortunate, widely known pattern, that causes so much backtracking that it often leads to situations like this, when the text is long and specific enough to lead to catastrophic backtracking.
Note that even [\w\W]*? (or [\s\S\r]*?, see Multi-line regular expressions in Visual Studio Code) here might already suffice. Although it also involves quite a lot of backtracking, it will be much more efficient.
What can usually be used is an unrolled pattern, like
<tag>(?:[^<\r]*(?:<(?!/tag>)[^<]*)*</tag>){4}
Instead of (.|\n)*?, a series of patterns are used so that each could only match distinct positions in a string.
Details
<tag> - a literal string(?:[^<\r]*(?:<(?!/tag>)[^<]*)*</tag>){4} - four repetitions of
[^<\r]* - 0 or more chars other than < (even line break chars, \r ensures this in VS Code regex, it enables all character classes in the pattern that can match newlines to match newlines (thus, \r is not necessary to use in the next character class))(?:<(?!/tag>)[^<]*)* - 0 or more repetitions of a < not followed with /tag> and then 0 or more chars other than <.</tag> - a literal </tag> string.Having said that, you might also be interested in the Emmet:Balace outward:
A well-known tag balancing: searches for tag or tag's content bounds from current caret position and selects it. It will expand (outward balancing) or shrink (inward balancing) selection when called multiple times. Not every editor supports both inward and outward balancing due of some implementation issues, most editors have outward balancing only.
Emmet’s tag balancing is quite unique. Unlike other implementation, this one will search tag bounds from caret’s position, not the start of the document. It means you can use tag balancer even in non-HTML documents.