Re: Subversion of user chosen major mode by Emacs.

[Alan Mackenzie <acm@muc.de>]

Hello, Dmitry.

On Wed, May 29, 2024 at 19:08:46 +0300, Dmitry Gutov wrote:
> Hi Alan,

> On 29/05/2024 15:51, Alan Mackenzie wrote:

> > On Wed, May 29, 2024 at 14:43:29 +0300, Dmitry Gutov wrote:
> >> On 29/05/2024 14:16, Alan Mackenzie wrote:
> >>>> I think this is a misfeature of `c-ts-mode.el`, but this was the result
> >>>> of a long discussion and I don't think we want to revisit that yet.
> >>> Why did nobody involve me in this discussion, considering that the
> >>> result involves "stealing" CC Mode users?

> >> This behavior is not new: loading a *-ts-mode has been overriding the
> >> user preferences since 2023-01-20 (commit 6b2f85caa6).

> > That has nothing to do with my point it is supposedly answering.

> > I've just had a look at that commit, and it simply adds entries to
> > auto-mode-alist for the *-ts-mode modes in the traditional, normal and
> > acceptable fashion.  CC Mode does the same.

> That's not the same thing: all CC Mode entries are behind ###autoload, 
> meaning that the alist does not actually change when you load the file 
> (as long as the autoloads are properly generated when you build Emacs).

Ah yes, you're right.  The entries to auto-mode-alist in cc-mode.el are
in comments (autoload comments), so that's one reason loading CC Mode
doesn't put those entries to the top of the alist.

To be honest, I'm surprised that c-ts-mode and friends haven't come to
have autoload entries for auto-mode-alist, superseding those in CC Mode.
Perhaps if this had been done, the unpleasantness caused by
major-mode-remap-alist/defaults could have been avoided.

> > The problem comes in a comment in that patch encouraging users to
> > subvert the proper meaning of c-mode, etc., from being specific modes to
> > being vague generic modes.  This is completely unnecessary for the
> > normal user who uses only the *-ts- modes and not CC Mode.  It is a
> > confusing mess for users who wish to use both of these, say for
> > comparison.

> >> Perhaps your personal customization for auto-mode-alist had been
> >> shielding you from the original issue. You can add a similar entry to
> >> major-mode-remap-alist.

> > Not sure what "original issue" you're referring to.  My customisation
> > for auto-mode-alist is an eval-after-load for c-ts-mode which deletes
> > the *-ts- entries from auto-mode-alist.  This has worked fine until
> > recently and should be restored to working again.

> Naturally, this only works while auto-mode-alist remains the last source 
> of truth regarding the mapping.

As it should.  major-mode-remap-alist and the other one add complexity to
Emacs, confuse users (as they have confused me) and add no worthwhile
facility to Emacs.

> > All this confusion in auto-mode-alist, and the horrible workarounds of
> > major-mode-remp_\(alist\|defaults\) result from a fundamental conceptual
> > error, namely changing c-mode and friends from having specific meanings
> > to being vague generic symbols.  THIS is what I should have been
> > consulted about, as the owner of these symbols.

> I agree that the terminology might be confusing. We've had a discussion 
> regarding adding the notion of "languages" to Emacs (I even posted a 
> proposal), but so far we decided to go with the "lighter" solution.

Again, the source of the current problem was the misuse of the symbols
c-mode and c++-mode to mean something other than the major modes in CC
Mode.  Again, nobody consulted me about this at all.

> > The latest symptom of this misunderstanding, which I bumped into
> > yesterday, is that Emacs changes the major mode of a C buffer with M-x
> > revert-buffer.  This is clearly unacceptable.

> And that started happening since commit 6b2f85caa6, you can look for the 
> related discussions and the objections that were voiced at the time.

To be clear, what I find unacceptable is Emacs maintainers presuming to
override options explicitly set by the user with settings the maintainers
think are better.  That is the purpose of major-mode-remap-defaults.
There are other, better ways to set up c-ts-mode as the default default
mode for C files.

-- 
Alan Mackenzie (Nuremberg, Germany).