You can browse compiler source code here with type annotation and code navigation if you like https://htzh.github.io/browse-ocaml/ . The editor plugins typically don't work on the compiler itself. These annotations and links were generated fairly painlessly from Ocaml compiler features (most hard work done by the compiler already).

Thanks for the links! I'll try to give it a read sometime.

But also, the editor plugins don't work on the compiler itself? Why's that? So you can't use Merlin on the OCaml compiler? That doesn't seem great.

And what's with the syntax highlighting being funky? The highlighter appears to think that a lot of these files have unterminated comments or string literals.