LLM for “talking to” a code repo? (like chatpdf.com, but for a codebase)

Is there a way (yet?) to add a chat layer to a codebase? Basically a layer that would take it's best guess at the ERD and functions after reading the code, then be able to articulate about it and respond to questions?

One of my biggest struggles is "getting to know" a codebase when I first walk up to it. I'm trying my best to get better, but I have to balance that with actually producing deliverables. It would help radically if a teammate (or better yet, the author!) could spend a few hours with me answering questions, but who has that kind of time! So an LLM wading through a codebase and then being able to sufficiently answer my questions about how modules relate, "what's [thisFunction] for?" and "where's the file that [doesThing]?" and the like would be absolutely something I would pay for.

Anything out there already? Is this an unmet market need, now that we know the tech is up to the challenge?