Everything you are talking about is useful for full-text search. It's practically pointless for code search. Trigrams definitely help for regex, you can make us

Everything you are talking about is useful for full-text search. It's practically pointless for code search. Trigrams definitely help for regex, you can make use of a trigram index for a quick false positive index lookup. Code and log search are two specialized use-cases of search that definitely warrant a non-full-text approach and as far as I am aware the trigram bitmap index would be considered state of the art for both. That isn't to say you can't solve the problem with a full-text search engine, many people do with the solutions you alluded to. However they are drastically less efficient and probably out of the question at Githubs scale.