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c3-ts-mode

This tree-sitter powered Emacs 29+ major mode provides syntax highlighting, indentation, imenu and which-function support for C3. It's built against the tree-sitter grammar located at https://github.com/c3lang/tree-sitter-c3.

[!WARNING] If you're updating, please do M-x treesit-install-language-grammar RET c3 RET to update the tree-sitter grammar too.

Installing

This mode requires Emacs 29 or greater for the built-in tree-sitter support.

Install the tree-sitter grammar

Add the source url to your treesit-language-source-alist.

(setq treesit-language-source-alist
  '((c3 "https://github.com/c3lang/tree-sitter-c3")))

If you already have a treesit-language-source-alist, you can also append to it using:

(add-to-list 'treesit-language-source-alist
  '(c3 "https://github.com/c3lang/tree-sitter-c3"))

Next, run M-x treesit-install-language-grammar RET c3 RET. (This requires cc to be available on your system.)

A libtree-sitter-c3.so should now be built and installed in your emacs directory.

Install the mode

Clone this repository and add:

(add-to-list 'load-path "path/to/c3-ts-mode")
(require 'c3-ts-mode)

Configuration

Set the indent offset using the c3-ts-mode-indent-offset variable:

(setq c3-ts-mode-indent-offset 2)

To enable all highlighting features, you might want to set treesit-font-lock-level to 4 (the default is 3):

(setq treesit-font-lock-level 4)

The default face for module paths is font-lock-constant-face. Override it by setting c3-ts-mode-module-path-face. The face name must be prefixed with @:

(setq c3-ts-mode-module-path-face '@font-lock-some-face-here)

The default face for assignments (see Notes) is font-lock-variable-name-face. Override it by setting c3-ts-mode-assignment-face. The face name must be prefixed with @:

(setq c3-ts-mode-assignment-face '@font-lock-some-face-here)

Further options:

;; Disable highlighting of variables
(setq c3-ts-mode-highlight-variable nil)
;; Disable highlighting of members
(setq c3-ts-mode-highlight-property nil)
;; Disable highlighting of punctuation
(setq c3-ts-mode-highlight-punctuation nil)
;; Disable highlighting of assignments
(setq c3-ts-mode-highlight-assignment nil)

Adding custom highlighting patterns

Here is an example how to override highlighting of the "assert" keyword and argument names:

(defun add-custom-c3-ts-rules ()
  (add-to-list 'treesit-font-lock-settings
               (car (treesit-font-lock-rules
                     :language 'c3
                     ;; Choose a feature name here (see docs for 'treesit-font-lock-rules')
                     :feature 'custom
                     ;; Use 't' to override the face, 'append'/'prepend' to append/prepend to existing ones
                     :override t
                     ;; This will highlight the "assert" keyword and argument names with custom faces
                     ;; See "37.5 Pattern Matching Tree-sitter Nodes" in the Emacs manual
                     '((assert_stmt "assert" @assert-face)
                       (call_invocation (call_arg name: (_) @named-arg-face)))
                     )) t)

  ;; Add feature 'custom' to feature level 4
  (push 'custom (nth 3 treesit-font-lock-feature-list)))

(add-hook 'c3-ts-mode-hook #'add-custom-c3-ts-rules)

Notes

• A special feature is that assignments (and updates via ++/--) are highlighted accurately.
  • If a variable or field is assigned, the variable name is highlighted.
  • If a pointer dereference is assigned, the asterisk is highlighted.
  • If an array element is assigned, the subscript brackets are highlighted.
  • You can configure this feature using c3-ts-mode-highlight-assignment and c3-ts-mode-assignment-face.
• If punctuation is enabled (treesit-font-lock-level is 4 and c3-ts-mode-highlight-punctuation is 't), make sure both font-lock-punctuation-face and font-lock-brackets-face is defined in your theme.
• Indentation is tricky and has a bunch of edge cases - please submit an issue if you find a case where it doesn't work as expected.