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Re: Unifying "foo-mode"s and "foo-ts-mode"s

From: Philip Kaludercic
Subject: Re: Unifying "foo-mode"s and "foo-ts-mode"s
Date: Fri, 30 Dec 2022 15:45:54 +0000

Theodor Thornhill <theo@thornhill.no> writes:

> On 30 December 2022 16:02:37 CET, Philip Kaludercic <philipk@posteo.net> 
> wrote:
>>Theodor Thornhill <theo@thornhill.no> writes:
>>> Philip Kaludercic <philipk@posteo.net> writes:
>>>> Theodor Thornhill <theo@thornhill.no> writes:
>>>>> Philip Kaludercic <philipk@posteo.net> writes:
>>>>>> Eli Zaretskii <eliz@gnu.org> writes:
>>>>>>> You can try.  I would like to start a full feature freeze in a day or
>>>>>>> two, so I'm not sure you will have enough time.  And it isn't like we
>>>>>>> didn't try various approaches during the past two months, so frankly I
>>>>>>> don't think that a better way even exists.  But if you come up with
>>>>>>> some very bright idea, who knows?
>>>>>> I have attached a sketch of my proposal with support for Python.
>>>>>> Instead of a separate python-ts-mode, we regulate tree-sitter support
>>>>>> using a user option `treesit-enabled-modes'.  It can either be a list
>>>>> [...]
>>>>> IIUC this will make all other config run before the treesit-related
>>>>> code?  
>>>> If that is the problem, that we can solve that by re-adjusting the order
>>>> in which the expanded code occurs. 
>>>>>        In that case I think this cannot work, because we _don't_ want to
>>>>> set all the before/after-change functions many modes set, for example.
>>>> What exactly is the issue here?  Can't we overwrite it again if
>>>> necessary?
>>> For example the CC modes set up lots of functions in the mode init, many
>>> of which override things like '*-function' variables, that if either not
>>> overriden explicitly by a treesit alternative or removed before mode
>>> init will impact performance.  There are some modes that will be worse
>>> in this regard than others, but one of my earlier suggestions was to
>>> just:
>>> (define-derived-mode foo ........
>>>   (cond
>>>     (use-treesit-p
>>>      (init-all-the-treesit-stuff))
>>>     (use-hypothetical-future-thing
>>>      (init-all-the-hypothetical-future-stuff))
>>>     (t
>>>      (init-all-the-other-stuff))))
>>This also looks good.
>>> In this case we don't let any code bleed in between the modes, which IMO
>>> is necessary.  At least we should be very careful with _when_ it is ok
>>> for such settings to bleed in.  Things like comment-start/end etc can
>>> bleed in just fine, but stuff like
>>> ```
>>>   (c-init-language-vars js-mode)
>>>   (setq-local indent-line-function #'js-indent-line)
>>>   (setq-local beginning-of-defun-function #'js-beginning-of-defun)
>>>   (setq-local end-of-defun-function #'js-end-of-defun)
>>>   (setq-local open-paren-in-column-0-is-defun-start nil)
>>>   (setq-local font-lock-defaults
>>>               (list js--font-lock-keywords nil nil nil nil
>>>                     '(font-lock-syntactic-face-function
>>>                       . js-font-lock-syntactic-face-function)))
>>>   (setq-local syntax-propertize-function #'js-syntax-propertize)
>>>   (add-hook 'syntax-propertize-extend-region-functions
>>>             #'syntax-propertize-multiline 'append 'local)
>>>   (add-hook 'syntax-propertize-extend-region-functions
>>>             #'js--syntax-propertize-extend-region 'append 'local)
>>>   (setq-local prettify-symbols-alist js--prettify-symbols-alist)
>>>   (setq-local parse-sexp-ignore-comments t)
>>>   (setq-local which-func-imenu-joiner-function #'js--which-func-joiner)
>>> ```
>>> Should absolutely not.
>>> Does that make sense?  I don't think this is impossible, but my biggest
>>> argument was that we need to keep things distinct, or at least be very
>>> explicit on when we share code.
>>Yes, I do understand this point, yet my impression has been that this
>>was not always necessary.  The relative complexity of cc-mode might
>>necessitate a separate mode, but I don't see why that should be the rule
>>instead of an exception?
> IIRC it was mostly because we wanted to start creating things instead of 
> bikeshedding over these details. 
> My thought process was to create separate modes now, and make a
> facility to map a language to a mode implementation. For example, imo
> it doesn't make sense for "the first" implementation to own a
> language's namespace. c-mode should be able to leverage cc-mode _or_
> c-ts-mode, rather than the other way around.

This is a good point, but as you say below this might be something that
we should aim towards for Emacs 30.

> At least during these months that seemed smart, because we have many
> contributions now due to the simple nature of creating a foo-ts-mode.

Some of which have been very superficial, leading to the dilemma that
users will have themselves with:  Do they want tree-sitter support or
the features of a more complete and mature mode.

> Surgically injecting tree sitter into existing modes is prone to
> error, and requires quite deep knowledge of each existing mode's inner
> working.
> So I'd just hold off and maybe create a nice facility for Emacs 30.
> Something like
> (setq major-mode-backend
>   '((c . cc-mode)
>     (c++ . treesit)))
> Then M-x c-mode would trigger cc, and c++-mode would trigger c++-ts-mode.
> And we keep the old implementations as the default until we know
> tree-sitter, has no disadvantages and swap the default. No need to
> deprecate anything or require config changes, imo.
> Theo

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