Re: [Emacs-diffs] trunk r116461: Connect electric-indent-mode up with CC Mode. Bug #15478.

[Dmitry Gutov]

Hi Alan,

On 26.03.2014 22:53, Alan Mackenzie wrote:

> Indentation (in the sense of what `indent-line-function' does) only makes
> sense in programming (etc.) modes.  In text modes, and the like,
> indentation is, in practice, done with adaptive fill prefices.

This could be considered a reason to improve the indent-line-function in 
text-mode. `indent-relative' offers behavior that's pretty close. Maybe 
it could be made to follow the behavior of auto-fill even closer.

> Having RET do `newline-and-indent' in Emacs Lisp Mode while doing
> `newline' in Text Mode makes a lot of sense to me.  A trickier question
> is to identify which of the non-programming modes really want this sort
> of indentation.

I'd rather make exceptions for specific "non-programming modes", where 
indentation of the next line is really hard to guess.

Many modes that don't inherit from prog-mode have something to do with 
structured content, and often define their own specific indentation 
functions (sgml-mode, markdown-mode inherit from text-mode, css-mode and 
yaml-mode inherit from fundamental-mode).

I'd really expect typing <div> and pressing RET in html-mode to offer 
hard +2 indentation on the next line, but I wouldn't call it a 
programming mode.

In Markdown, I'm often typing code blocks, and I expect RET to bring me 
to the column which the previous line was indented to, so I don't have 
to press TAB each time. And if I'm outside of a code block, the lines 
usually either have no indentation (then indent-relative indents to the 
0th column as well), or they serve as continuation of a paragraph, and I 
want each next line to have the same extra indentation until the 
paragraph ends (and indent-relative does that well enough).

The last time I used text-mode, it was for a similar purpose (a couple 
of code blocks, and the rest of the text is indented to column 0).

`M-x fill-paragraph' would slaughter the code blocks, and it wouldn't 
improve the indentation anywhere else.

It also eats line breaks that were put in manually. A good example is 
ChangeLog files: we often see cleanup commits in Emacs that change the 
places where the lines are broken, for better readability, in ways that 
fill-paragraph is unable to do automatically.

And if ChangeLog files didn't always magically have the right 
indentation (one tab), and one had to fix it with `fill-paragraph', all 
the manual line breaks would be mangled, each time. It still happens 
when I fix lines that are too long this way.

> > There's a certain class of users who've been binding RET to
> > `newline-and-indent' for a long time (myself included), and I haven't
> > seen anyone mention only doing that in prog-mode, instead of globally.
>
> That was what we collectively decided last Autumn when the topic came up.

Okay: I haven't seen anyone mention doing it outside of emacs-devel.

> Richard Stallman alluded to it in his disgust at bug #16156, when what
> was bound to RET at the time zapped his indentation.
>
> I personally would not be unhappy at leaving the traditional binding in
> place for RET and C-j, but wouldn't mind them swapping in "indenting"
> modes.  I'd object strongly to RET in text mode messing around with
> indentation.

Maybe text-mode by itself should be a special case. I don't use it often 
enough to have a strong opinion.

> > How hard can it be for a user to change the key bindings without a mode?
>
> Middling, not very.  Such a minor mode might serve to damp down the
> inevitable complaints the change in defaults will provoke.

As long as this new mode is divorced from electric-indent-mode, I'd be 
happy.

> By "makes sense" I think you mean "seems a sensible thing to do".  I take
> issue with you here and say that, in Text Mode, it's a bizarre thing to
> do.  I can't think of any normal circumstances where this behaviour would
> be commonly desired; just how often in Text Mode do you not want RET just
> to insert a new line when you type it at the beginning of a line?

This specific behavior is a consequence of using `newline-and-indent'. 
One answer may be "Don't want that? Use `open-line'", which I sometimes 
do, but special-casing indent-line-function in text-mode not to reindent 
on the first invocation (when point is at bol followed by whitespace and 
then non-whitespace on the same line) could well be another option.

What makes sense to me, is using `newline-and-indent' itself. Richard 
doesn't like

foo
|  bar

turning into

foo

|bar

I can understand that, but I don't like

foo
  bar|baz

turning into

foo
  bar
|baz  (note the missing indentation)

Which situation do you think occurs more frequently?