[NeoVim lsp] Unable to find root directory

[anzhi0708]

The error message from ~/.local/state/nvim/lsp.log:

[START][2023-03-13 22:40:41] LSP logging initiated
[WARN][2023-03-13 22:40:41] .../lua/vim/lsp.lua:1065	"server_request: no handler found for"	"workspace/diagnostic/refresh"
[WARN][2023-03-13 22:40:41] .../lua/vim/lsp.lua:1065	"server_request: no handler found for"	"workspace/diagnostic/refresh"
[START][2023-03-13 22:41:19] LSP logging initiated
[WARN][2023-03-13 22:41:19] ...lsp/handlers.lua:487	'failed to poll dune registry. Unix.Unix_error(Unix.ENOENT, "stat", "/Users/aj/.local/share/dune/rpc")'

OCaml version:

➜  hello_world ocaml --version
The OCaml toplevel, version 5.0.0

OPAM version:

➜  hello_world opam --version
2.1.4

Packages installed:

# Packages matching: installed
# Name                # Installed # Synopsis
base-bigarray         base
base-bytes            base        Bytes library distributed with the OCaml comp
base-domains          base
base-nnp              base        Naked pointers prohibited in the OCaml heap
base-threads          base
base-unix             base
chrome-trace          3.7.0       Chrome trace event generation library
cmdliner              1.1.1       Declarative definition of command line interf
cppo                  1.6.9       Code preprocessor like cpp for OCaml
csexp                 1.5.1       Parsing and printing of S-expressions in Cano
dot-merlin-reader     4.6         Reads config files for merlin
dune                  3.7.0       Fast, portable, and opinionated build system
dune-build-info       3.7.0       Embed build information inside executable
dune-configurator     3.7.0       Helper library for gathering system configura
dune-rpc              3.6.2       Communicate with dune using rpc
dyn                   3.6.2       Dynamic type
fiber                 3.6.2       Structured concurrency library
lambda-term           3.3.1       Terminal manipulation library for OCaml
logs                  0.7.0       Logging infrastructure for OCaml
lwt                   5.6.1       Promises and event-driven I/O
lwt_react             1.2.0       Helpers for using React with Lwt
merlin-lib            4.8-500     Merlin's libraries
mew                   0.1.0       Modal editing witch
mew_vi                0.5.0       Modal editing witch, VI interpreter
ocaml                 5.0.0       The OCaml compiler (virtual package)
ocaml-base-compiler   5.0.0       Official release 5.0.0
ocaml-config          3           OCaml Switch Configuration
ocaml-lsp-server      1.15.1-5.0  LSP Server for OCaml
ocaml-options-vanilla 1           Ensure that OCaml is compiled with no special
ocamlbuild            0.14.2      OCamlbuild is a build system with builtin rul
ocamlc-loc            3.6.2       Parse ocaml compiler output into structured f
ocamlfind             1.9.6       A library manager for OCaml
ocamlformat-rpc-lib   0.25.1      Auto-formatter for OCaml code (RPC mode)
ocplib-endian         1.2         Optimised functions to read and write int16/3
octavius              1.2.2       Ocamldoc comment syntax parser
omd                   1.3.2       A Markdown frontend in pure OCaml
ordering              3.6.2       Element ordering
pp                    1.1.2       Pretty-printing library
ppx_yojson_conv_lib   v0.15.0     Runtime lib for ppx_yojson_conv
re                    1.10.4      RE is a regular expression library for OCaml
react                 1.2.2       Declarative events and signals for OCaml
result                1.5         Compatibility Result module
seq                   base        Compatibility package for OCaml's standard it
spawn                 v0.15.1     Spawning sub-processes
stdune                3.6.2       Dune's unstable standard library
topkg                 1.0.7       The transitory OCaml software packager
trie                  1.0.0       Strict impure trie tree
uchar                 0.0.2       Compatibility library for OCaml's Uchar modul
user-setup            0.7         Helper for the configuration of editors for t
utop                  2.11.0      Universal toplevel for OCaml
uucp                  15.0.0      Unicode character properties for OCaml
uuseg                 15.0.0      Unicode text segmentation for OCaml
uutf                  1.0.3       Non-blocking streaming Unicode codec for OCam
xdg                   3.7.0       XDG Base Directory Specification
yojson                2.0.2       Yojson is an optimized parsing and printing l
zed                   3.2.1       Abstract engine for text edition in OCaml

NeoVim OCaml LSP configuration (init.lua):

lspconfig.ocamllsp.setup {
  filetypes = { "ocaml", "ocaml.menhir", "ocaml.interface", "ocaml.ocamllex", "reason", "dune" },
  root_dir = lspconfig.util.root_pattern("*.opam", "esy.json", "package.json", ".git", "dune-project", "dune-workspace"),
  on_attach = on_attach,
  capabilities = capabilities
}

(At first I simply tried lspconfig.ocamllsp.setup {} but no success, same error message as above config. I also tried to add 'ml' to root_dir but still no luck. Instead of lspconfig.util.root_pattern, I also tried another form of root_dir configuration, basically a lua table if I remembered correctly, but still got the same error when started to edit a .ml buffer)

Note

ocamllsp confirmed working, because helix(editor) uses the exact same binary ($ which ocamllsp) and everything works fine on helix

➜  hello_world hx --health ocaml
Configured language server: ocamllsp
Binary for language server: /Users/aj/.opam/OCaml5BaseCompiler/bin/ocamllsp
Configured debug adapter: None
Highlight queries: ✓
Textobject queries: ✘
Indent queries: ✓

So I'm somewhat confused, both helix and neovim uses default configuration but neovim lsp is not working

[rgrinberg]

The error message from neovim is expected - it just means you don't have dune running in watch mode. ocamllsp should work as expected.

[anzhi0708]

The error message from neovim is expected - it just means you don't have dune running in watch mode. ocamllsp should work as expected.

Thanks a lot for replying!

I'm a beginner in OCaml, and that's why I really need LSP related tools to help me learn OCaml.

Could you kindly show me how to set dune in watch mode, so that I can use ocamllsp within nvim? Appreciate it!

[Khady]

you can add --watch to basically any dune build command. But as mentioned earlier this is not necessary for ocamllsp to work. Having dune running in watch mode will add some features like reporting of errors happening outside of the file you are currently editing.

[rsulli55]

@anzhi0708 I just ran into the same issue, the LSP wasn't working in a directory with a plain ocaml source file. I was able to resolve it by running git init on the directory, which forced the root directory to be populated and the LSP to actually attach. I think any file listed under root_dir here would suffice to have root directory be found and the L:SP should work after that.

[josecastillolema]

Thanks @rsulli55 the workaround works. However, is there a way to disable this root_dir requirement? The same folder without .git, .opam files, etc. works fine on VSCode, however it does not on NeoVim.

Workaround #2:

lspconfig.ocamllsp.setup {
  filetypes = { "ocaml", "ocaml.menhir", "ocaml.interface", "ocaml.ocamllex", "reason", "dune" },
  root_dir = lspconfig.util.root_pattern("*.opam", "esy.json", "package.json", ".git", "dune-project", "dune-workspace", "*.ml"),
  on_attach = on_attach,
  capabilities = capabilities
}