Re: Use (eval-when-compile 'treesit) to save us from writing declare-function forms

[Eli Zaretskii <eliz@gnu.org>]

> From: Yuan Fu <casouri@gmail.com>
> Date: Wed, 4 Dec 2024 10:19:42 -0800
> Cc: emacs-devel@gnu.org
> 
> 
> 
> > On Dec 3, 2024, at 5:12 AM, Eli Zaretskii <eliz@gnu.org> wrote:
> > 
> > I don't understand" c-ts-mode.el already does
> > 
> >  (require 'treesit)
> > 
> > So what would eval-when-compile add to that?
> 
> When Emacs is built without tree-sitter, none of the treesit.c functions are available (except for treesit-ready-p). Now if this Emacs compiles c-ts-mode.el, it’ll signal undefined function error for all those functions. So we add declare-function forms for all the treesit.c functions used in c-ts-mode.el, and have to update the declare-function forms whenever we use some new treesit.c functions.
> 
> If we use eval-when-compile, we don’t need to write declare-function forms in c-ts-mode.el anymore, because treesit.el has declare-function forms for all treesit.c functions.

That's what I don't understand: how will eval-when-compile which loads
treesit.el be different from (require 'treesit) we already have in
c-ts-mode?  Don't they both load treesit.el?