I got bitten recently by haproxy using the '!' prefix on .gitignore lines to negate previous lines. This resulted in ag silently not searching any of the code base at all. So if you're implementing .gitignore support, you may want to consider at worst bailing on files with this syntax (and perhaps other syntax that is not supported)

ag bug: https://github.com/ggreer/the_silver_searcher/issues/1233