How to pass --fallback-read-dot-merlin to ocamllsp in vscode-ocaml-platform extension?

Ecosystem
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1

In a project that uses OMicroB, vscode is unable to find the cmi files which are installed outside of opam’s sandbox in /usr/local/lib/omicrob. How can I set up the vscode-ocaml-platform extension to look in that directory? Is there a way to pass --fallback-read-dot-merlin to ocamllsp used by the extension?

2

We also use this feature for Melange. You can find instructions here

3

In theory that’s what I need. In practice I’m not able to get it to work. Here’s my vscode config:

{
    "ocaml.sandbox": {
        "kind": "custom",
        "template": "opam exec --switch=4.14.0 --set-switch -- $prog $args --fallback-read-dot-merlin"
    }
}

My .merlin file is fine because it works with vim. But vscode still does not find the cmi’s in /usr/local/lib/omicrob.

4

vscode extension has a setting called extraEnv which allows to pass env vars to ocamllsp, but last I checked this didn’t work for me :sweat_smile:

edit: this actually works

5

On a side note: I’m very happy to see support for dot-merlin added back into ocaml-lsp, I’m still a big user of .merlin files.

Anyone know how to pass a command line argument on Emacs lsp-mode?

6

How can I set up the vscode-ocaml-platform extension to look in that directory? Is there a way to pass --fallback-read-dot-merlin to ocamllsp used by the extension?

You’ll want your project-root/.vscode/settings.json to look like this:

    {
        // whatever
        "ocaml.server.args": [ "--fallback-read-dot-merlin" ],
        // existing crud
    }

You’ll also want to put an empty dune-project file in your project root directory because of an ocaml-lsp bug: .merlin based projects still require a blank dune-project file · Issue #859 · ocaml/ocaml-lsp · GitHub.

This works for me on a very small project that is built with a tiny bash script and has an extremely simple 7 line long .merlin file.