Re: Tree-sitter and major mode inheritance

[Eli Zaretskii]

> Date: Sun, 20 Nov 2022 01:42:04 +0200
> Cc: Eli Zaretskii <eliz@gnu.org>, emacs-devel@gnu.org,
>  monnier@iro.umontreal.ca, theo@thornhill.no
> From: Dmitry Gutov <dgutov@yandex.ru>
> 
> On 20.11.2022 01:36, Yuan Fu wrote:
> > If we keep js-mode as-is, and add js-base-mode and js-ts-mode, 
> > (derived-mode-p ‘js-mode) should keep working as before, or maybe I’m 
> > msiunderstanding your question?
> 
> (derived-mode-p 'js-mode) will return nil in js-ts-mode.
> 
> Which could be a problem when this call is used as a substitute for a 
> file type check (e.g. "are we editing a JavaScript file?"), which is one 
> of its common uses.

This test can only work on the assumption that there's a single parent mode
for all the modes which support a given programming language.  This is a
fragile assumption, so code which is based on it is broken and should be
fixed.

IOW, I don't think we should feel ourselves bound by this fragile
assumption (assuming the solution we decide on breaks it).