GNU bug report logs - #15478
cc-mode does not obey electric-indent-mode

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From: Alan Mackenzie <acm <at> muc.de>
To: Stefan Monnier <monnier <at> iro.umontreal.ca>
Cc: gnu-emacs-bug <at> moderators.isc.org
Subject: bug#15478: cc-mode does not obey electric-indent-mode
Date: Mon, 7 Oct 2013 20:37:38 +0000

'Evening, Stefan.

On Mon, Oct 07, 2013 at 12:14:19PM -0400, Stefan Monnier wrote:
> >> Emacs has never provided this feature in any mode that I know, cc-mode
> >> included.  Some major modes (such as CC-mode) try to provide some vague
> >> approximation of it, using "electric keys" that trigger indentation
> >> "often enough" that it works more or less OK in some common cases.
> > :-).  I think CC Mode DTRT practically 100% of the time.  There haven't
> > been bug reports asking for the details of the electric indentation to be
> > improved.

> I can assure you it doesn't work 100%: in many circumstances you have to
> hit TAB (or M-C-\ or M-C-q) manually before the text's indentation
> reflects the modifications that took place.

Electric indentation only works on the current line, and I'm not sure
extending it to subsequent lines would be a good idea.  Could you specify
cases where it doesn't work on the current line?

> I don't think it's a failure of your code, tho (and
> electric-indent-mode fails in the exact same way).

How do they fail?

> > from 1992.  Somebody (RMS?  Barry Warsaw?) clearly thought it very
> > important.

> I thought it's important enough to embark on electric-indent-mode
> (which is reasonably easy to implement, except it's hellish to get all
> the various authors to get back in line and start using the generic
> infrastructure, for the long term benefit of end users, at the cost
> of short term disruption and extra work).

;-).  That, you should have expected. It's a standard conflict of
interests - those of Emacs (as a whole) against those of the individual
modes.  Having all the arguments, though, will result in a better
electric-indent-mode which interacts better with the other modes.

> >> The core is then: how should we make cc-mode integrate better with Emacs
> >> and use the generic electric-*-mode functionality instead of
> >> rolling its own?

> > How about aliasing `c-electric-mode' and `electric-indent-mode' and
> > making them buffer-local in CC Mode buffers?  Then setting CC Mode's
> > value of `electric-indent-chars' to nil, for now, and in the medium
> > future (once e-i-m has percolated through to old versions and XEmacs)
> > integrating CC Mode into electric-indent-mode properly?

> Poor, but does satisfy the requirements.

Do you want to elaborate?

> > How about introducing `global-electric-indent-mode' and redefining e-i-m
> > to be buffer-local?  Or, alternatively, leaving e-i-m as it is and
> > defining `local-electric-indent-mode'?

> `electric-indent-local-mode' sounds good.

> > What about defining a property `no-electric-indentation' which could
> > be set on python-mode and others?

> I wouldn't use a property.  Just a buffer-local variable
> `electric-indent-inhibit' which those modes can set.
> For Python and Haskell, this should only inhibit *re*indentation, while
> still calling indent-according-to-mode after inserting a newline.

Electric indentation is precisely about the *re*indation of the current
line, isn't it?  indent-according-to-mode after NL isn't electric
indentation.

> >> For the record: CC-mode is not the only major mode in this boat.
> >> I've already converted several major modes to use electric-indent-mode,
> >> and for some of them this also involved changing the default behavior.

> > Would you identify (some of) these modes, please, so I can go and have a
> > look.

> If you "grep electric-indent- **/*.el" you'll find some of them (I also
> changed a few external ones like sml-mode).

OK, I'll do this.

> Note that in most cases I made the change by completely side-stepping
> the old code (i.e. the define-key that rebinds the keys to electric
> versions was either removed or made conditional on something like
> (fboundp 'electric-indent-mode)).

> And those were usually simpler than what cc-mode does, with the
> exception maybe of octave.el where the old behavior was a bit more
> complex, and replaced by a mix of electric-indent-mode,
> electric-layout-mode.

> But in most of those cases, I only made a minimal effort at trying to
> preserve old behavior and user's customization.  I've seen a few
> questions about "why foo-mode doesn't indent as before", and the answer
> "it's now controlled by electric-indent-mode" always seemed to satisfy
> the user.

OK.

>         Stefan

-- 
Alan Mackenzie (Nuremberg, Germany).

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