bug#61211: 28.2; Feature request; facility for dispatch type major mode

bug#61211: 28.2; Feature request; facility for dispatch type major mode

[Ikumi Keita]

I'd like to discuss dispatch functions or "superficial" major modes.
AUCTeX has the following major mode functions:
context-en-mode, context-nl-mode, japanese-latex-mode, japanese-plain-tex-mode
They only do language-specific set-ups and turn into context-mode,
latex-mode or plain-tex-mode eventually. In some aspects, they are
similar with dispatch functions `tex--guess-mode' and `TeX-tex-mode'
(AUCTeX) which guess a proper major mode and call it:
- They can be specified as `mode' tag of file local variable and entry
  of `auto-mode-alist'.
- They never hold their own `major-mode' value.
- When called, they eventually turn into another proper major mode.
For these reasons, they can be called "superficial" major modes.

Note that it isn't enough to define them like
(define-derived-mode japanese-latex-mode latex-mode "LaTeX"
  ...
  (setq major-mode 'latex-mode)
  ...)
because it doesn't respond to directory local variable entry of the form
((japanese-latex-mode
  ...))
in that case.

So I hope emacs to have facility to handle such superficial major modes
in a clean way.

Regards,
Ikumi Keita
#StandWithUkraine #StopWarInUkraine



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bug#61211: 28.2; Feature request; facility for dispatch type major mode

[Yuan Fu]

Ikumi Keita <ikumi@ikumi.que.jp> writes:

> I'd like to discuss dispatch functions or "superficial" major modes.
> AUCTeX has the following major mode functions:
> context-en-mode, context-nl-mode, japanese-latex-mode, japanese-plain-tex-mode
> They only do language-specific set-ups and turn into context-mode,
> latex-mode or plain-tex-mode eventually. In some aspects, they are
> similar with dispatch functions `tex--guess-mode' and `TeX-tex-mode'
> (AUCTeX) which guess a proper major mode and call it:
> - They can be specified as `mode' tag of file local variable and entry
>   of `auto-mode-alist'.
> - They never hold their own `major-mode' value.
> - When called, they eventually turn into another proper major mode.
> For these reasons, they can be called "superficial" major modes.
>
> Note that it isn't enough to define them like
> (define-derived-mode japanese-latex-mode latex-mode "LaTeX"
>   ...
>   (setq major-mode 'latex-mode)
>   ...)
> because it doesn't respond to directory local variable entry of the form
> ((japanese-latex-mode
>   ...))
> in that case.
>
> So I hope emacs to have facility to handle such superficial major modes
> in a clean way.
>
> Regards,
> Ikumi Keita
> #StandWithUkraine #StopWarInUkraine

Another use-case is for tree-sitter modes: we want to dispatch to
tree-sitter/non-tree-sitter major modes automatically.

Yuan

bug#61211: 28.2; Feature request; facility for dispatch type major mode

[Ikumi Keita]

>>>>> Yuan Fu <casouri@gmail.com> writes:
> Another use-case is for tree-sitter modes: we want to dispatch to
> tree-sitter/non-tree-sitter major modes automatically.

Yeah, reasonable consideration.

Regards,
Ikumi Keita
#StandWithUkraine #StopWarInUkraine

bug#61211: 28.2; Feature request; facility for dispatch type major mode

[Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors]

> I'd like to discuss dispatch functions or "superficial" major modes.
> AUCTeX has the following major mode functions:
> context-en-mode, context-nl-mode, japanese-latex-mode, japanese-plain-tex-mode
> They only do language-specific set-ups and turn into context-mode,
> latex-mode or plain-tex-mode eventually. In some aspects, they are
> similar with dispatch functions `tex--guess-mode' and `TeX-tex-mode'
> (AUCTeX) which guess a proper major mode and call it:
> - They can be specified as `mode' tag of file local variable and entry
>   of `auto-mode-alist'.
> - They never hold their own `major-mode' value.
> - When called, they eventually turn into another proper major mode.
> For these reasons, they can be called "superficial" major modes.
>
> Note that it isn't enough to define them like
> (define-derived-mode japanese-latex-mode latex-mode "LaTeX"
>   ...
>   (setq major-mode 'latex-mode)
>   ...)

IOW what are the advantages/disadvantages of using (setq major-mode
'latex-mode) above?

Also, this seems different from the case of dispatch functions like
`tex--guess-mode' and `TeX-tex-mode' since these may end up choosing
`latex-mode` but they're definitely not "child" of `latex-mode`.

[ Similarly for the tree-sitter case mentioned in another message: the
  function that dispatches to TS-vs-nonTS major modes can't be considered
  a child of those two major modes.  ]

> because it doesn't respond to directory local variable entry of the form
> ((japanese-latex-mode
>   ...))
> in that case.

If we make `japanese-latex-mode` a proper child mode, then this problem
disappears, right?

I'm also thinking that maybe `set-auto-mode` should remember the name of
the "mode function" it called so we could consult this (in addition to
the value of `major-mode`) when applying directory-local vars?


        Stefan

bug#61211: 28.2; Feature request; facility for dispatch type major mode

[Ikumi Keita]

>>>>> Stefan Monnier <monnier@iro.umontreal.ca> writes:
>> Note that it isn't enough to define them like
>> (define-derived-mode japanese-latex-mode latex-mode "LaTeX"
>> ...
>> (setq major-mode 'latex-mode)
>> ...)

> IOW what are the advantages/disadvantages of using (setq major-mode
> 'latex-mode) above?

The rest of the codes are written without considering japanese-*
variants. For example there are codes like
(if (eq major-mode 'LaTeX-mode) ...)
(if (memq major-mode (nth 4 TeX-command-list)) ...)
(assq major-mode ALIST-WITHOUT-JAPANESE-VARIANTS)

Of course, we can "fix" these codes to cover japanese-* variants like
(if (memq major-mode '(LaTeX-mode japanese-LaTeX-mode) ...))
(let ((mode (if (string-prefix-p (symbol-name major-mode) "japanese-")
                (intern (substring 9 major-mode))
              major-mode)))
   (memq mode (nth 4 TeX-command-list)) ...)
(let ((mode (if (string-prefix-p (symbol-name major-mode) "japanese-")
                (intern (substring 9 major-mode))
              major-mode)))
   (assq mode ALIST-WITHOUT-JAPANESE-VARIANTS))

However, such treatments don't look good to me.

It is true that we could make wrapper function/macro to reduce such
complexity. However, practically all third party packages developed by
non-Japanese wouldn't notice the necesity of such wrapper for the first
place and write simply like
(if (eq major-mode 'LaTeX-mode) ...)
; such codes, incompatible with japanse-LaTeX-mode, will continue to
spawn on ELPA, MELPA, stackexchange etc. (or even in AUCTeX itself after
I cease to participate develop, unless a new Japanese developer joins.)

> Also, this seems different from the case of dispatch functions like
> `tex--guess-mode' and `TeX-tex-mode' since these may end up choosing
> `latex-mode` but they're definitely not "child" of `latex-mode`.

Yes, not the same, only a similarity.

>> because it doesn't respond to directory local variable entry of the form
>> ((japanese-latex-mode
>> ...))
>> in that case.

> If we make `japanese-latex-mode` a proper child mode, then this problem
> disappears, right?

Yes, restricting the scope only within the availability of directory
local variables.

> I'm also thinking that maybe `set-auto-mode` should remember the name
> of the "mode function" it called so we could consult this (in addition
> to the value of `major-mode`) when applying directory-local vars?

If that's possible, it will be a solution, I think.

Regards,
Ikumi Keita
#StandWithUkraine #StopWarInUkraine