[maxov]

SemanticDB (https://scalameta.org/docs/semanticdb/guide.html) is a protobuf-based file format that does almost exactly this for JVM languages, primarily Scala (I was a contributor a while back). It is used to build an intelligent online code browser, as the backend for a language server, and to do intelligent refactorings.

I think a language-agnostic semantic metadata format is a good idea, but requires a lot of compromise. ctags partially does this, but only to a very coarse level (mostly definitions and references). I think some ctags implementations also define 'extension fields' that could be used to give type information, but I don't know how/if these are used in practice. SemanticDB is extremely fine-grained, but highly specialized to JVM languages and type systems that are designed to work with the JVM. Finding a common set of semantic features that can be used across languages and type systems that is fine-grained enough to be more useful than ctags sounds very difficult to me.

[dymk]

I think simple things like "go to reference" or "show type" would be sufficient for 95% of usecases. But if you split languages up into a few different categories (maybe along the lines of Algol-like vs Lisp-like), and were flexible with extensions, I'd imagine we'd see some common patterns emerging, and clients would take advantage of that. Best effort is probably good enough to greatly improve the ergonomics of search.