Ocaml-lsp can't find the generated OCaml code (e.g. _build/default/src/lib/ast.ml)

[Timmmm]

I've been doing some work on Sail using VSCode with ocaml-lsp, which is surprisingly good, except that it can't find any of the code that's generated at compile time. In particular _build/default/src/lib/ast.ml, which is used all over the place.

I can't find any "additional include directories" style options in ocaml-lsp , which is what you'd typically do for C++, Python, etc. Just wondering if you have any idea how to fix this.

[Alasdair]

Even though it can't find the code (for go to definition), it should still work for completion/inline type annotations I think?

[bacam]

I think you're right about it finding the compiled version (as it's in the same place as all of the other compiled files). Poking at it a little, it's the underlying "merlin" tool that can't find the source file, so you can see the same effect in (e.g.) emacs on Linux too. The part I don't understand is why - the dune build tool knows about the file, and it provides information to merlin.

[Timmmm]

Hmm yeah I think it's treating ast.ml as an installed library: ocaml/dune#6397

The workaround seems to be to use manually written .merlin files, but Dune doesn't generate them any more, and dune ocaml dump-dot-merlin / dune ocaml merlin dump-config seem to be broken for me (No merlin configuration found.).

I might ask on StackOverflow or maybe the Merlin repo.

[bacam]

It's not quite that; it's that dune tells it where to find the compiled files, but not the source. Perhaps that's because alongside the generated files there are also copies of the plain source files, and it doesn't want merlin to refer editors to those to prevent you from editing the wrong one.

However, you might be able to use a manually altered .merlin file, you just need to give dump-dot-merlin at path: dune ocaml dump-dot-merlin src/lib/

[bacam]

(Which also confirms that it's dune that's not telling merlin where to look.)

[Timmmm]

you just need to give dump-dot-merlin at path

Ah would be nice if the docs mentioned that! So that does give some output and dune ocaml merlin dump-config src/lib gives similar output.

I tried putting the dump-dot-merlin output in .merlin, and it's definitely reading it (tested via the age-old "add sdkfgjhgdsfkgjhd and see if it complains" method). I then add this to the VSCode config:

    "ocaml.server.args": [
        "--fallback-read-dot-merlin"
    ],

But after that it basically fails to resolve anything, including stuff that's in the same directory, e.g. open Rewriter. Hmm.