Re: Tree-sitter and major mode inheritance

[Dmitry Gutov]

On 20.11.2022 09:28, Eli Zaretskii wrote:
> > 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.

Technically correct, the best kind of correct.

> This is a
> fragile assumption, so code which is based on it is broken and should be
> fixed.

Okay then, but then we'll need to learn another way to ask that 
question. Previously, we did try to ensure (not always successfully) a 
single inheritance chain between such modes.