opam, dune & Cram Support

neocaml includes dedicated tree-sitter modes for opam and dune files, plus a mode for dune's cram test files. neocaml-opam-mode activates automatically for .opam, .opam.template, and bare opam files; neocaml-dune-mode activates for dune, dune-project, and dune-workspace files (including variants like dune-workspace.ci). Both provide font-lock, indentation, and imenu.

opam lint

neocaml-opam-mode registers an opam lint flymake backend so you get inline diagnostics for missing fields, deprecated constructs, and syntax errors. To enable it, activate flymake-mode in opam buffers:

(add-hook 'neocaml-opam-mode-hook #'flymake-mode)

flycheck users get opam lint support out of the box via flycheck's built-in opam checker.

dune Commands

neocaml-dune-interaction-mode is a minor mode that provides keybindings for running common dune commands from any neocaml buffer. All commands run via compile, so you get error navigation (M-g n / M-g p), clickable source locations, and the full compilation-mode interface.

Enable it in OCaml buffers:

(add-hook 'neocaml-base-mode-hook #'neocaml-dune-interaction-mode)

Or in all neocaml-related buffers (including dune and opam files):

(dolist (hook '(neocaml-base-mode-hook
               neocaml-dune-mode-hook
               neocaml-opam-mode-hook))
  (add-hook hook #'neocaml-dune-interaction-mode))

Available commands (all under the C-c C-d prefix):

Keybinding	Command	Description
C-c C-d b	neocaml-dune-build	Build the project
C-c C-d t	neocaml-dune-test	Run tests
C-c C-d c	neocaml-dune-clean	Clean build artifacts
C-c C-d p	neocaml-dune-promote	Promote test corrections
C-c C-d f	neocaml-dune-fmt	Format code
C-c C-d u	neocaml-dune-utop	Launch utop with project libraries
C-c C-d r	neocaml-dune-exec	Run an executable (prompts for name)
C-c C-d d	neocaml-dune-command	Run any dune command (with history)
C-c C-d .	neocaml-dune-find-dune-file	Find the nearest dune file

With a prefix argument (C-u), build, test, and fmt commands run in watch mode (--watch), rebuilding automatically when files change. For example, C-u C-c C-d b runs dune build --watch.

The project root is determined by walking up from the current file to find dune-project.

If Emacs doesn't inherit your opam environment (common when launching from a desktop shortcut), you can prefix all dune commands with opam exec --:

(setq neocaml-dune-use-opam-exec t)

dune File Formatting

neocaml-dune-mode can format the current buffer using dune format-dune-file. Use C-c C-f (neocaml-dune-format-buffer) to format on demand, or enable automatic formatting on save:

(setq neocaml-dune-format-on-save t)

Note: this formats individual dune files via dune format-dune-file, which is different from dune fmt (available via C-c C-d f) that formats the entire project.

Completion

Both neocaml-dune-mode and neocaml-opam-mode add a completion-at-point function, so M-x completion-at-point (C-M-i) offers context-aware candidates. They also plug into UIs built on completion-at-point, like the built-in completion-preview-mode, corfu, and company.

In dune files you get:

• stanza names (library, executable, rule, ...) at the head of a top-level form
• field names for the enclosing stanza (so a library offers libraries, modules, public_name, ... while a rule offers targets, deps, action, ...)
• library names inside libraries and pps fields - both your own project's libraries (scanned from its dune files) and the installed findlib libraries (from ocamlfind list)

In opam files you get:

• field and section names (synopsis, depends, build, url, ...) at the start of a line
• package names inside the depends, depopts, and conflicts fields, sourced from opam list

The external candidate sources are cached per project. Run M-x neocaml-dune-refresh-libraries or M-x neocaml-opam-refresh-packages after changing your opam switch or adding a library to pick up the change. You can turn the external sources off with neocaml-dune-complete-libraries and neocaml-opam-complete-packages; the static stanza/field completion keeps working either way and needs no OCaml tooling installed.

Project-local switches

When the project root has a local switch (an _opam/ directory), the library and package lists are gathered through opam exec -- from that root, so the project's switch is used automatically - no configuration needed. For a global switch where Emacs doesn't inherit the opam environment (e.g. a GUI Emacs launched from a desktop shortcut), set neocaml-dune-use-opam-exec / neocaml-opam-use-opam-exec to force the listings through opam exec -- as well. This mirrors the same option used for dune commands.

Cram Tests

neocaml-cram-mode provides syntax highlighting for cram test (.t) files, as used by dune's expect-test framework. It highlights shell commands, expected output, output modifiers ((re), (glob), (no-eol), (esc)), exit codes, and prose comments.

The mode activates automatically for .t files. Use dune promote (available via C-c C-d p with neocaml-dune-interaction-mode) to accept corrected test output.

Note

The .t extension is also used by Perl test files. If you work with both OCaml and Perl, you may need to override the association for Perl projects:

;; Use cperl-mode for .t files in Perl projects
(add-to-list 'auto-mode-alist '("/t/.*\\.t\\'" . cperl-mode))

Entries added later to auto-mode-alist take priority, so the more specific pattern above will win for .t files under a t/ directory (Perl convention).