:lang rust +tree-sitter: rustic-beginning-of-function fails with void-function rust-in-str-or-cmnt

[unship]

What happened?

In a Rust buffer, calling rustic-beginning-of-function errors with:

Symbol’s function definition is void: rust-in-str-or-cmnt

Expected behavior

rustic-beginning-of-function should move to the beginning of the current Rust function without error.

Steps to reproduce

1. Enable Rust with tree-sitter:

   :lang
   (rust +lsp +tree-sitter)

2. Open a Rust buffer using rustic-mode.

3. Call M-x rustic-beginning-of-function.

Why it seems to happen

rustic-beginning-of-function calls rustic-beginning-of-defun, which calls rust-in-str-or-cmnt:

;; rustic-interaction.el
(rust-in-str-or-cmnt)

That helper is defined by classic rust-mode in rust-prog-mode.el:

(defun rust-in-str-or-cmnt () (nth 8 (syntax-ppss)))

But with Doom's Rust tree-sitter path, rust-mode-treesitter-derive makes rust-mode derive from Emacs' built-in rust-ts-mode, so rust-prog-mode.el is not loaded. rustic still assumes the classic helper exists, so the function is void.

Local workaround

This fixes it locally:

(after! rustic-interaction
  (unless (fboundp 'rust-in-str-or-cmnt)
    (defun rust-in-str-or-cmnt () (nth 8 (syntax-ppss)))))

Possible fix

Doom could provide this compatibility shim when :lang rust +tree-sitter and rustic are used together, or avoid the rustic path that depends on classic rust-mode internals.

Versions

GNU Emacs 31.1
Doom modules commit: d57ab52a3
rustic commit: 4afbca4
rust-mode commit: 0058837