Symfony version(s) affected: >=4.4.12

Description

I'm trying to exclude a directory and its content. I have a configuration similar to the one described in #37560. I'm trying to keep all the content in /example/test/.

/example/**
!/example/example.txt
!/example/packages
!/example/packages/example.yaml
!/example/test/

This configuration will only retain the /example/test directory, but not its content. If I try a .gitignore like the one below, PCRE breaks completely:

/example/**
!/example/example.txt
!/example/packages
!/example/packages/example.yaml
!/example/test*

PCRE doesn't handle lookbehind that don't have a fixed length. So the above .gitignore file will cause preg_match(): Compilation failed: lookbehind assertion is not fixed length warnings. This, in turn, causes the whole .gitignore regex to not work and none of the rules get enforced.