Re: Make all tree-sitter modes optional

[Eli Zaretskii <eliz@gnu.org>]

> Date: Mon, 16 Jan 2023 01:39:18 +0200
> Cc: emacs-devel@gnu.org
> From: Dmitry Gutov <dgutov@yandex.ru>
> 
> On 15/01/2023 16:01, Eli Zaretskii wrote:
> > You will
> > see that where possible, just loading a TS mode modifies
> > auto-mode-alist if the tree-sitter support for that mode is available,
> > whereas for other modes auto-mode-alist is modified only when the mode
> > is actually turned on successfully for the first time.  This is
> > because some of the TS modes have their own *.el files, whereas others
> > share a .el file with other modes, and so loading that file doesn't
> > necessarily means the user wants to use the tree-sitter based mode.
> 
> If we *are* going to do this (make all ts mode strictly optional), I 
> don't think either of this is a good idea: for a given foo-ts-mode, the 
> user might already have an auto-mode-alist entry configured with another 
> mode (third-party or not), and they will likely 'M-x foo-ts-mode' to try 
> how well it works (or doesn't).
> 
> Having auto-mode-alist modified automatically can come as a surprise 
> either way.
> 
> Note the this is different to having the auto-mode-alist entries set up 
> from the outset, because the user's alterations override those.
> 
> We can drop the auto-mode-alist alterations from ts modes altogether, to 
> bring them back when we do decide to enable them by default.

Like I said: this is not ideal.  So I'm not surprised that whatever we
do, there can be usage scenarios where what we do will annoy someone.

That said:

  . The proposed patch made many changes of auto-mode-alist
    conditional where they previously were _un_conditional.  I submit
    that this is less annoyance in the important use case where the
    tree-sitter or the grammar library is not available.  There are
    indications that this situation will be frequent enough when Emacs
    29.1 hits the street.

  . I don't buy the assumption that customizations of auto-mode-alist
    are frequent enough to make that an important factor in these
    decisions, let alone suggest that users should always do that if
    they want to try the *-ts-* modes seriously:

      - IME, auto-mode-alist is relatively rarely customized for modes
        that are included in Emacs (e.g., I don't customize entries of
        any such modes), for the simple reason that it is very rarely
        needed.
      - Customizing auto-mode-alist is not the easiest task, it
        requires good knowledge of Emacs regexps and alists.  So
        asking anyone who wants to try using the tree-sitter modes to
        do that is not the best idea from the POV of user-friendliness.
      - OTOH, I'm quite sure that people who do already customize
        auto-mode-alist for built-in modes are more advanced users and
        will be able to overcome any problems that could be caused by
        modifying auto-mode-alist as side effect of activating the
        mode.

  . Last, but not least: I think someone who turns on a tree-sitter
    mode in some buffer is much more likely to want to use that mode
    in more than that single buffer than the other way around.  And if
    for some reason they are disappointed soon enough, just restarting
    the Emacs session will get them back the old behavior.  Which
    again tells me that if we accept your proposal, we will annoy more
    users (with the need to modify auto-mode-alist) than under my
    proposal.

So, on balance, I think what I proposed is better than what you
propose.