bug#15478: cc-mode does not obey electric-indent-mode

[Alan Mackenzie]

Hello, Stefan.

On Sat, Oct 05, 2013 at 09:10:01PM -0400, Stefan Monnier wrote:
> > The default for CC Mode must be on, otherwise automatic indentation
> > is broken.

> IIUC your notion of "automatic indentation" is that the text is kept
> indented without the user hitting TAB, just as a side-effect of editing
> the text.

Yes.

> 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.

> But while CC-mode has been doing that for "ever", it's not nearly as
> important as you claim, as demonstrated by all the other major modes
> that don't even try to do that.

There's a difference between a feature never having been implemented, and
taking it away (even the default value) after it has.  Electric
indentation was in CC Mode in the very first version I have available,
from 1992.  Somebody (RMS?  Barry Warsaw?) clearly thought it very
important.

> > > Please, let's keep this bug-report's focus: making cc-mode obey
> > > electric-indent-mode.  Discussion of default setting of
> > > electric-indent-mode belongs elsewhere.
> > These two things are inextricably entangled.

> No they're not.  And I think it's blatantly obvious, even to you.
> I understand that simply to mean that you do not want CC-mode's default
> behavior to change.

You're not wrong there.

> So, for the sake of it, from here on, let's please continue this
> discussion under the premise that electric-indent-mode will be enabled
> by default.

OK.

> 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?

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

> 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.

> I delayed touching at cc-mode mostly because I know you're
> very opinionated ;-)

:-).  

>         Stefan

-- 
Alan Mackenzie (Nuremberg, Germany).