Eli Zaretskii <eliz@gnu.org> writes:

> You can try.  I would like to start a full feature freeze in a day or
> two, so I'm not sure you will have enough time.  And it isn't like we
> didn't try various approaches during the past two months, so frankly I
> don't think that a better way even exists.  But if you come up with
> some very bright idea, who knows?

I have attached a sketch of my proposal with support for Python.
Instead of a separate python-ts-mode, we regulate tree-sitter support
using a user option `treesit-enabled-modes'.  It can either be a list

--8<---------------cut here---------------start------------->8---
  (setq treesit-enabled-modes '(python-mode c-mode))
--8<---------------cut here---------------end--------------->8---

or generally enable tree-sitter

--8<---------------cut here---------------start------------->8---
  (setq treesit-enabled-modes t)
--8<---------------cut here---------------end--------------->8---

All a major modes has to do is pass a parser configuration

--8<---------------cut here---------------start------------->8---
  (define-derived-mode python-mode prog-mode "Python"
    "Major mode for editing Python files.

  \\{python-mode-map}"
    :syntax-table python-mode-syntax-table
    :parser-conf python-mode--treesit-conf
   ...
--8<---------------cut here---------------end--------------->8---

that expands to

--8<---------------cut here---------------start------------->8---
  (when-let
      ((conf python-mode--treesit-conf)
       ((cond
         ((listp treesit-enabled-modes)
          (memq 'python-mode treesit-enabled-modes))
         ((eq treesit-enabled-modes t))))
       ((treesit-ready-p
         (nth 0 conf)))
       (parser
        (treesit-parser-create
         (nth 0 conf))))
    (setq-local treesit-font-lock-feature-list
                (nth 1 conf)
                treesit-font-lock-settings
                (nth 2 conf)
                treesit-defun-name-function
                (nth 3 conf)
                treesit-defun-type-regexp
                (nth 4 conf)
                imenu-create-index-function
                (nth 5 conf))
    (treesit-major-mode-setup))
--8<---------------cut here---------------end--------------->8---

at *the end* of the major mode definition.  Note that if no parser
configuration was parsed, the entire expression is byte-compiled away,
so there is no run-time overhead for other modes.

The parser configuration is currently a list but if might as well be a
vector, a structure or anything else.  This is just a rushed proposal to
meet the deadline.  How does it look like?