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bug#60176: 29.0.60; Fallback file variable mode if treesitter is not usa
From: |
Juri Linkov |
Subject: |
bug#60176: 29.0.60; Fallback file variable mode if treesitter is not usable |
Date: |
Mon, 19 Dec 2022 09:39:14 +0200 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/30.0.50 (x86_64-pc-linux-gnu) |
> It would be nice if the fallback mode is used when treesitter is not
> usable. Say for example, for the following file variable in a C file:
>
> /* -*- mode: c; mode: c-ts; -*- */
>
> If c-ts-mode is not usable (regardless of whether the mode is
> available), activate c-mode instead.
>
> This bug is regarding the automatically loaded mode when a file with some
> mode is set, and not regarding the user explicitly setting the mode.
>
> Supporting this can help me use multiple mode file variables regardless
> of the GNU Emacs version used by co-developers.
'major-mode-remap-alist' should be able to handle this requirement
since its design is similar to MIME.TYPES and MAILCAP. But actually
MAILCAP supports an additional predicate TEST that is a command
executed to determine whether or not the mailcap line applies.
So to completely cover all needs, 'major-mode-remap-alist' should
support a predicate as well. For example,
(setq major-mode-remap-alist '((c-mode #'treesit-available-p c-ts-mode)))
or a more complex predicate:
(setq major-mode-remap-alist '((c-mode (lambda ()
(and (treesit-available-p)
(treesit-ready-p 'c t)))
c-ts-mode)))