[ANN] Dune Developer Preview Updates

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The instructions on https://preview.dune.build configures dune preview for emacs via lsp-mode.

I was able to configure eglot to use dune tools exec ocamllsp with the following configuration. The snippet configures: tuareg, eglot (for dune preview), ocaml-eglot (copied from its official README).

Caveat: ocamlformat isn’t working. I don’t know where I can specify dune tools exec ocamlformat in this setup. Any help is appreciated. After tracing the relevant portions of codebases, I figured out that all eglot does is send a formatting request to ocamllsp because ocamllsp claims to provide formatting capabilities. The onus of finding ocamlformat is on ocamllsp, which simply looks for ocamlformat binary on PATH.

I didn’t find a “proper” way (like a command line argument) to pass the path of ocamlformat binary to ocamllsp. So, updating PATH it is. PATH="$(dirname $(dune tools which ocamlformat)):$PATH" emacs from terminal does the job. I would appreciate a better approach than this.

(use-package tuareg
  :ensure t)

;; configure eglot's ocaml setup to use `dune tools exec ocamllsp`
;; TODO: ocamlformat has stopped working.
;; I don't know how to configure `dune tools exec ocamlformat`.
(use-package eglot
  :config
  (add-to-list 'eglot-server-programs
         '(((caml-mode :language-id "ocaml")
            (ocaml-ts-mode :language-id "ocaml")
            (tuareg-mode :language-id "ocaml") reason-mode)
          . ("dune" "tools" "exec" "ocamllsp"))))

(use-package ocaml-eglot
  :ensure t
  :after tuareg
  :hook
  (tuareg-mode . ocaml-eglot)
  (ocaml-eglot . eglot-ensure)
  (ocaml-eglot . (lambda () 
                   (add-hook #'before-save-hook #'eglot-format nil t))))

Now launch emacs from terminal with an updated PATH so that ocamllsp can find ocamlformat binary in emacs.

$ PATH="$(dirname $(dune tools which ocamlformat)):$PATH" emacs
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