VSCode instrumentation

[epatrizio]

Hello, In vscode, it seems that ocaml-lsp automatically launches the instrumentation and does it incorrectly.
I made a minimal example using mutaml. Here are the steps to reproduce:

$ git clone https://github.com/jmid/mutaml.git
$ cd mutaml
$ opam install .
$ cd ..
$ git clone https://github.com/epatrizio/mutaml_exp.git
$ cd mutaml_exp
$ git checkout vscode

Then, open VSCode on mutaml_exp. If you open any .ml file (e.g. lib/lib.ml) and put your mouse focus on it, you'll see some files appearing in the sources.

There are two issues there:

• first, the instrumentation should not run automatically
• second, the files end up in the wrong place (you can compare to what happen when you run dune runtest --instrument-with mutaml not from vscode), they end-up in lib/ when they should be somewhere in _build/.

Thanks a lot!

[rgrinberg]

Thanks for the report. I think this is a bug in dune.

[zapashcanon]

FYI it's not happening when using dune+merlin from neovim or my terminal directly, we only managed to trigger it from vscode.

[rgrinberg]

I'm really surprised by that. Lsp/Merlin is just launching whatever dune tells it to. If anyone would like to try their hand at the fix, the issue is how we construct the preprocess that we provide Merlin.make:

  let preprocess =
    Preprocess.Per_module.with_instrumentation lib.buildable.preprocess
      ~instrumentation_backend:
        (Lib.DB.instrumentation_backend (Scope.libs scope))
  in

We should always just drop the instrumentation for merlin