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#+TITLE: Neovim, OCaml Interfaces, Tree-Sitter and LSP
Can we all agree that witnessing syntax highlighting being absolutely off is
probably the most annoying thing that can happen to anybody?
I mean, just look at this horror.
#+CAPTION: Syntax highlighting being absolutely wrong
#+NAME: fig:wrong-highlingting
[[../img/wrong-highlighting.png]]
What you are looking at is the result of trying to enable ~tree-sitter~ for
OCaml hacking and calling it a day. In a nutshell, OCaml ~mli~ files are
quickly turning into a random mess of nonsensical colors, and I didn’t know
why. I tried to blame
[[https://github.com/tree-sitter/tree-sitter-ocaml/issues/72][~tree-sitter-ocaml~]],
but of course I was wrong.
The issue is subtle, and to be honest, I don’t know if I totally grasp it. But
from my rough understanding, it breaks down as follows.
- ~tree-sitter-ocaml~ defines two grammars: ~ocaml~ for the ~ml~ files, and
~ocaml_interface~ (but ~ocamlinterface~ also works) for the ~mli~ files
- By default, neovim uses the filetype ~ocaml~ for ~mli~ files, so the incorrect
parser is being used for syntax highlighting. This explains the root issue
- Bonus: ~ocamllsp~ does not recognize the ~ocamlinterface~ filetype by
default (but somehow use the ~ocaml.interface~ id for ~mli~ files…[fn::There
is probably something to be done here.])
So, in order to have both ~tree-sitter~ and ~ocamllsp~ working at the same time,
I had to tweak my configuration a little bit.
#+begin_src lua
lspconfig.ocamllsp.setup({
cmd = { 'ocamllsp', '--fallback-read-dot-merlin' },
-- Necessary to get tree sitter to work with .mli files
filetypes = vim.list_extend(
require('lspconfig.server_configurations.ocamllsp')
.default_config
.filetypes,
{ 'ocamlinterface' }
),
})
vim.cmd([[au! BufNewFile,BufRead *.mli setfiletype ocamlinterface]])
#+end_src
And now, I am blessed with a consistent syntax highlighting for my ~mli~ files.
#+CAPTION: Syntax highlighting being absolutely wrong
#+NAME: fig:wrong-highlingting
[[../img/good-highlighting.png]]
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