bug#13133: 24.2.90; scroll-conservatively is too coarse a setting

bug#13133: 24.2.90; scroll-conservatively is too coarse a setting

[Dmitry Gutov]

I think this value is used in contexts that are different enough to
behave differently in this respect.

Examples:
1) I want help-button-action to bring me to the function's definition,
and I generally want in the middle of the screen. Same for imenu, etc.
2) I really don't want to see empty space after the contents in the
compilation window. But as much as half of the window may be empty right
after compilation because of the point recentering.
3) Ideally, if I move around with next/previous-line, I don't want
sudden jumps and recenterings. Same thing with beginning/end-of-defun
(so setting scroll-conservatively to a value larger than 0 is not a real
solution).

Thoughts?

So far I'm doing this for the compilation buffer:

(defun compile-scroll-eob (buffer _status)
  (let ((win (get-buffer-window buffer))
        (current (selected-window)))
    (when win
      (select-window win)
      (with-current-buffer buffer
        (when (> (line-number-at-pos (point-max)) (window-height))
          (goto-char (point-max))
          (recenter (window-height))))
      (select-window current))))

(add-to-list 'compilation-finish-functions 'compile-scroll-eob)

I think that behavior should be the default, though.

In GNU Emacs 24.2.90.1 (x86_64-unknown-linux-gnu, GTK+ Version 3.6.0)
 of 2012-11-26 on vbx
Bzr revision: 110959 rgm@gnu.org-20121126014100-0199uq4y2fo0cnaz
Windowing system distributor `The X.Org Foundation', version 11.0.11300000
System Description:	Ubuntu 12.10

bug#13133: 24.2.90; scroll-conservatively is too coarse a setting

[Eli Zaretskii]

> From: Dmitry Gutov <dgutov@yandex.ru>
> Date: Mon, 10 Dec 2012 07:29:40 +0400
> 
> I think this value is used in contexts that are different enough to
> behave differently in this respect.
> 
> Examples:
> 1) I want help-button-action to bring me to the function's definition,
> and I generally want in the middle of the screen. Same for imenu, etc.
> 2) I really don't want to see empty space after the contents in the
> compilation window. But as much as half of the window may be empty right
> after compilation because of the point recentering.
> 3) Ideally, if I move around with next/previous-line, I don't want
> sudden jumps and recenterings. Same thing with beginning/end-of-defun
> (so setting scroll-conservatively to a value larger than 0 is not a real
> solution).

I'm sorry, but the problem you describing is entirely unclear to me.
You didn't say what value, if any, did you set scroll-conservatively
to, nor if you have any other scroll-* variables customized to
non-default values.  If you don't customize anything, Emacs always
re-centers when point goes out of sight.  When point is re-centered, I
don't think you can ever have half-window of empty space, because of
the way re-centering works.

Given this lack of information, I don't understand how you get the
adverse effects in your 3 examples.  Please elaborate, perhaps
separately about each of the examples.

Thanks.

bug#13133: 24.2.90; scroll-conservatively is too coarse a setting

[Dmitry Gutov]

On 10.12.2012 10:30, Eli Zaretskii wrote:
>> From: Dmitry Gutov <dgutov@yandex.ru>
>> Date: Mon, 10 Dec 2012 07:29:40 +0400
>>
>> I think this value is used in contexts that are different enough to
>> behave differently in this respect.
>>
>> Examples:
>> 1) I want help-button-action to bring me to the function's definition,
>> and I generally want in the middle of the screen. Same for imenu, etc.
>> 2) I really don't want to see empty space after the contents in the
>> compilation window. But as much as half of the window may be empty right
>> after compilation because of the point recentering.
>> 3) Ideally, if I move around with next/previous-line, I don't want
>> sudden jumps and recenterings. Same thing with beginning/end-of-defun
>> (so setting scroll-conservatively to a value larger than 0 is not a real
>> solution).
>
> I'm sorry, but the problem you describing is entirely unclear to me.
> You didn't say what value, if any, did you set scroll-conservatively
> to, nor if you have any other scroll-* variables customized to
> non-default values.  If you don't customize anything, Emacs always
> re-centers when point goes out of sight.  When point is re-centered, I
> don't think you can ever have half-window of empty space, because of
> the way re-centering works.
>
> Given this lack of information, I don't understand how you get the
> adverse effects in your 3 examples.  Please elaborate, perhaps
> separately about each of the examples.

The problem is getting all 3 to work at the same time.

For 1, scroll-conservatively needs to be < 100, something like 0-10, so 
that recentering usually happens.
For 2, I have to set scroll-conservatively to 101. Some lower values may 
also help, but there's no guarantee, as I understand it: the contents of 
the compilation buffer are getting added in large chunks.
For 3, again, I have to set scroll-conservatively to a large value. For 
C-n/C-p, the value of 5 is usually enough, for for C-M-e/C-M-a, it often 
has to be larger than that.

Half-window happens because when the compilation buffer is filled, the 
point is at the end of it (when compilation-scroll-output is t, at least).

Of other scroll- variables, I have scroll-preserve-screen-position set 
to t. Didn't think that matters.

bug#13133: 24.2.90; scroll-conservatively is too coarse a setting

[Eli Zaretskii]

> Date: Mon, 10 Dec 2012 10:46:51 +0400
> From: Dmitry Gutov <dgutov@yandex.ru>
> CC: 13133@debbugs.gnu.org
> 
> >> Examples:
> >> 1) I want help-button-action to bring me to the function's definition,
> >> and I generally want in the middle of the screen. Same for imenu, etc.
> >> 2) I really don't want to see empty space after the contents in the
> >> compilation window. But as much as half of the window may be empty right
> >> after compilation because of the point recentering.
> >> 3) Ideally, if I move around with next/previous-line, I don't want
> >> sudden jumps and recenterings. Same thing with beginning/end-of-defun
> >> (so setting scroll-conservatively to a value larger than 0 is not a real
> >> solution).
> >
> > I'm sorry, but the problem you describing is entirely unclear to me.
> > You didn't say what value, if any, did you set scroll-conservatively
> > to, nor if you have any other scroll-* variables customized to
> > non-default values.  If you don't customize anything, Emacs always
> > re-centers when point goes out of sight.  When point is re-centered, I
> > don't think you can ever have half-window of empty space, because of
> > the way re-centering works.
> >
> > Given this lack of information, I don't understand how you get the
> > adverse effects in your 3 examples.  Please elaborate, perhaps
> > separately about each of the examples.
> 
> The problem is getting all 3 to work at the same time.
> 
> For 1, scroll-conservatively needs to be < 100, something like 0-10, so 
> that recentering usually happens.
> For 2, I have to set scroll-conservatively to 101. Some lower values may 
> also help, but there's no guarantee, as I understand it: the contents of 
> the compilation buffer are getting added in large chunks.
> For 3, again, I have to set scroll-conservatively to a large value. For 
> C-n/C-p, the value of 5 is usually enough, for for C-M-e/C-M-a, it often 
> has to be larger than that.

Why can't you use a value of scroll-conservatively around 10, then?
The way I see it, the only problem might be with 2, and even there I'm
not sure you will see it frequently, or ever.  For 3, C-M-e/C-M-a will
DTRT and show point in the middle of the window, unless the function
is very short, in which case point will be near the beginning or end
of the window; again, TRT.

> Half-window happens because when the compilation buffer is filled, the 
> point is at the end of it (when compilation-scroll-output is t, at least).

Does this happen with or without setting scroll-conservatively to a
value larger than 100?

Just for the record: when I asked whether people who like Emacs to
_never_ recenter would mind having that behavior in contexts that have
nothing to do with scrolling, the response was a huge YES.  So the
current behavior seems to be "by popular demand".

Another possibility would be to add more customization values to
compilation-scroll-output, implementing the behavior of your
compile-scroll-eob.

I won't argue what the default behavior should be, because it tends to
become bike-shedding very fast.  FWIW, I use the default behavior,
without customizing any scroll-related variables, and like that
behavior, including in compilation buffers.

bug#13133: 24.2.90; scroll-conservatively is too coarse a setting

[Dmitry Gutov]

On 10.12.2012 11:08, Eli Zaretskii wrote:
>> Date: Mon, 10 Dec 2012 10:46:51 +0400
>> From: Dmitry Gutov <dgutov@yandex.ru>
>> CC: 13133@debbugs.gnu.org
>>
>>>> Examples:
>>>> 1) I want help-button-action to bring me to the function's definition,
>>>> and I generally want in the middle of the screen. Same for imenu, etc.
>>>> 2) I really don't want to see empty space after the contents in the
>>>> compilation window. But as much as half of the window may be empty right
>>>> after compilation because of the point recentering.
>>>> 3) Ideally, if I move around with next/previous-line, I don't want
>>>> sudden jumps and recenterings. Same thing with beginning/end-of-defun
>>>> (so setting scroll-conservatively to a value larger than 0 is not a real
>>>> solution).
>>>
>>> I'm sorry, but the problem you describing is entirely unclear to me.
>>> You didn't say what value, if any, did you set scroll-conservatively
>>> to, nor if you have any other scroll-* variables customized to
>>> non-default values.  If you don't customize anything, Emacs always
>>> re-centers when point goes out of sight.  When point is re-centered, I
>>> don't think you can ever have half-window of empty space, because of
>>> the way re-centering works.
>>>
>>> Given this lack of information, I don't understand how you get the
>>> adverse effects in your 3 examples.  Please elaborate, perhaps
>>> separately about each of the examples.
>>
>> The problem is getting all 3 to work at the same time.
>>
>> For 1, scroll-conservatively needs to be < 100, something like 0-10, so
>> that recentering usually happens.
>> For 2, I have to set scroll-conservatively to 101. Some lower values may
>> also help, but there's no guarantee, as I understand it: the contents of
>> the compilation buffer are getting added in large chunks.
>> For 3, again, I have to set scroll-conservatively to a large value. For
>> C-n/C-p, the value of 5 is usually enough, for for C-M-e/C-M-a, it often
>> has to be larger than that.
>
> Why can't you use a value of scroll-conservatively around 10, then?

Just tried that with compilation, didn't help. In fact, I have to set it 
as large as 50 to not see empty space in the window (tried 40, no dice).
And that's with one specific compilation process. Run something that's 
twice as verbose, and the value will have to be 100, no?

> The way I see it, the only problem might be with 2, and even there I'm
> not sure you will see it frequently, or ever.  For 3, C-M-e/C-M-a will
> DTRT and show point in the middle of the window, unless the function
> is very short, in which case point will be near the beginning or end
> of the window; again, TRT.

Like I mentioned, I don't want C-M-e/C-M-a to recenter. Why do you think 
it's TRT?
As far as I'm concerned, recentering might be fine when we go to the end 
of a small function (it will fit on the screen anyway), but a larger 
function, which might have fit on the full screen, will be cut in half.

>> Half-window happens because when the compilation buffer is filled, the
>> point is at the end of it (when compilation-scroll-output is t, at least).
>
> Does this happen with or without setting scroll-conservatively to a
> value larger than 100?

Without.

> Just for the record: when I asked whether people who like Emacs to
> _never_ recenter would mind having that behavior in contexts that have
> nothing to do with scrolling, the response was a huge YES.  So the
> current behavior seems to be "by popular demand".

If I had to guess, it might be that people just wanted out of the 
default always-recentering behavior, and it was a quick way to end the 
discussion and get the implementation.

Anyway, I don't remember seeing that poll. And if you were asking on 
emacs-devel, that doesn't exactly represent the majority of users.

I don't think I'm asking for anything exotic here, really. I think all 3 
items are pretty much the standard in "modern" editors or IDEs.

> Another possibility would be to add more customization values to
> compilation-scroll-output, implementing the behavior of your
> compile-scroll-eob.

Yes, sure. Just set buffer-local value of scroll-conservatively, maybe?

But that won't help with C-M-a/C-M-e and, I don't know, any other 
buffers with deal with process output? I think the compilation buffer is 
a great example that not only doesn't have anything to do with 
scrolling, but also is unrelated to code navigation. And still, 
scroll-conservatively is used there.

> I won't argue what the default behavior should be, because it tends to
> become bike-shedding very fast.  FWIW, I use the default behavior,
> without customizing any scroll-related variables, and like that
> behavior, including in compilation buffers.

Do you like the behavior of compilation buffer often having wasted 
space, or do you just not mind it (with monitors being cheap and all)? I 
don't see what anyone could really like about it.

bug#13133: 24.2.90; scroll-conservatively is too coarse a setting

[Eli Zaretskii]

> Date: Mon, 10 Dec 2012 12:28:58 +0400
> From: Dmitry Gutov <dgutov@yandex.ru>
> CC: 13133@debbugs.gnu.org
> 
> Like I mentioned, I don't want C-M-e/C-M-a to recenter. Why do you think 
> it's TRT?

Because you generally want to see the entire definition of the API,
not just the opening brace or paren.

> As far as I'm concerned, recentering might be fine when we go to the end 
> of a small function (it will fit on the screen anyway), but a larger 
> function, which might have fit on the full screen, will be cut in half.

IMO, C-M-e/C-M-a is not for observing the whole function.  You may be
looking for a separate feature, or maybe a modification of an existing
feature.

> >> Half-window happens because when the compilation buffer is filled, the
> >> point is at the end of it (when compilation-scroll-output is t, at least).
> >
> > Does this happen with or without setting scroll-conservatively to a
> > value larger than 100?
> 
> Without.

Can you cook up a test case?  I'd like to see why this happens.  (If
showing this requires injection of specific amount of text into the
compilation buffer, you could use 'cat' or some similar program to do
so, instead of actually running a compiler.)

> > Just for the record: when I asked whether people who like Emacs to
> > _never_ recenter would mind having that behavior in contexts that have
> > nothing to do with scrolling, the response was a huge YES.  So the
> > current behavior seems to be "by popular demand".
> 
> If I had to guess, it might be that people just wanted out of the 
> default always-recentering behavior, and it was a quick way to end the 
> discussion and get the implementation.
> 
> Anyway, I don't remember seeing that poll. And if you were asking on 
> emacs-devel, that doesn't exactly represent the majority of users.

Emacs 24.x with this feature was released 6 months ago, and I have yet
to see a single complaint about it -- until now.  What user poll can
possibly match that?

> > Another possibility would be to add more customization values to
> > compilation-scroll-output, implementing the behavior of your
> > compile-scroll-eob.
> 
> Yes, sure. Just set buffer-local value of scroll-conservatively, maybe?

Could be.  But I think it is best first to define the required
behavior first.  Then we can see if setting scroll-conservatively
would fit the bill.

> But that won't help with C-M-a/C-M-e and, I don't know, any other 
> buffers with deal with process output?

"M-x shell" comes to mind.

> > I won't argue what the default behavior should be, because it tends to
> > become bike-shedding very fast.  FWIW, I use the default behavior,
> > without customizing any scroll-related variables, and like that
> > behavior, including in compilation buffers.
> 
> Do you like the behavior of compilation buffer often having wasted 
> space, or do you just not mind it (with monitors being cheap and all)? I 
> don't see what anyone could really like about it.

Very simple: I don't watch the compilation messages as they come in.
It's a waste of time; I continue editing or doing something else while
the compiler churns away.  To me, watching the messages is a relic
from old DOS days when I couldn't do anything while waiting for the
compiler to finish.

I only look at the compiler messages when compilation finishes, and
then I either scroll through the buffer or use "C-x `".  In both
cases, what redisplay does when a new message comes in is of no
interest to me.

bug#13133: 24.2.90; scroll-conservatively is too coarse a setting

[Dmitry Gutov]

On 10.12.2012 12:52, Eli Zaretskii wrote:
>> Date: Mon, 10 Dec 2012 12:28:58 +0400
>> From: Dmitry Gutov <dgutov@yandex.ru>
>> CC: 13133@debbugs.gnu.org
>>
>> Like I mentioned, I don't want C-M-e/C-M-a to recenter. Why do you think
>> it's TRT?
>
> Because you generally want to see the entire definition of the API,
> not just the opening brace or paren.

Not sure if I understand you here. For example, if I'm in an Elisp 
function, I can press C-M-a to go to its beginning, and the whole 
definition (including arglist and docstring) will be visible. If the 
value of scroll-conservatively is small, though, the function body may 
be cut in half.
Or do you specifically mean non-lisp languages where the docstring is 
above the function definition?

>> As far as I'm concerned, recentering might be fine when we go to the end
>> of a small function (it will fit on the screen anyway), but a larger
>> function, which might have fit on the full screen, will be cut in half.
>
> IMO, C-M-e/C-M-a is not for observing the whole function.  You may be
> looking for a separate feature, or maybe a modification of an existing
> feature.

I don't think you can reasonably decide what they are for. When a 
command moves viewport, I think it's reasonable to use it for that 
purpose. Not that that's the only purpose I use them for, but in general 
I prefer when the body of a function displayed in a buffer is not split 
in half.

Also, I'd prefer if end-of-definition's behavior didn't depend on the 
length of the function it acts on. It's a little disorienting.

>>>> Half-window happens because when the compilation buffer is filled, the
>>>> point is at the end of it (when compilation-scroll-output is t, at least).
>>>
>>> Does this happen with or without setting scroll-conservatively to a
>>> value larger than 100?
>>
>> Without.
>
> Can you cook up a test case?  I'd like to see why this happens.  (If
> showing this requires injection of specific amount of text into the
> compilation buffer, you could use 'cat' or some similar program to do
> so, instead of actually running a compiler.)

Here's one:

~/tesh.sh:

#!/bin/bash
for i in `seq 1 125`;
do
     echo "Lorem ipsum"
done

eval:

(setq scroll-conservatively 10)

(let ((compilation-scroll-output t)) (compile "~/test.sh"))

In the end, in 54-line window, the text "Compilation finished" ends up 
on line 26.

>>> Just for the record: when I asked whether people who like Emacs to
>>> _never_ recenter would mind having that behavior in contexts that have
>>> nothing to do with scrolling, the response was a huge YES.  So the
>>> current behavior seems to be "by popular demand".
>>
>> If I had to guess, it might be that people just wanted out of the
>> default always-recentering behavior, and it was a quick way to end the
>> discussion and get the implementation.
>>
>> Anyway, I don't remember seeing that poll. And if you were asking on
>> emacs-devel, that doesn't exactly represent the majority of users.
>
> Emacs 24.x with this feature was released 6 months ago, and I have yet
> to see a single complaint about it -- until now.  What user poll can
> possibly match that?

Not sure. But it is a low-level feature that's not exactly trivial to 
reason about. So a user might not think it's a bug worth reporting, even 
if they don't like the behavior.

For example, when I migrated to Emacs 24, I remember reading about the 
improvements to scroll-conservatively, so setting it to 101 was one of 
the first things I did. Then I noticed that it makes imenu and 
help-button-action only scroll as far as the first line of the function 
definition, which is something I don't believe anyone can find optimal.
So I set the variable value to 5, which allowed next/previous-line 
scrolling without recentering, and at the same time usually makes code 
navigation commands recenter. I haven't used compilation buffer much 
until recently. But this value of 5 is bad in subtle ways.

Aside from what I mentioned about compilation, *-of-defun, *-sentence 
and similar commands, the behavior of imenu and help-button-action that 
comes with any positive value of scroll-conservatively is strange. Sure, 
that's a rare case, but what if the function I'm looking for is 3 or 5 
lines below the last window line? Then imenu won't recenter on it. That 
makes no sense.

I'd rather they used some other variable that allowed to specify the 
number of lines that the function I navigated to is allowed to be from 
the window boundary. Closer than 4 lines? Recenter! Or maybe always 
recenter, or put the first line of the function at 1/3rd of the window 
height from the top.

>> But that won't help with C-M-a/C-M-e and, I don't know, any other
>> buffers with deal with process output?
>
> "M-x shell" comes to mind.

It passes my test case. Calling ~/test.sh doesn't make the prompt line 
scroll to the middle of the window. Same for inf-ruby (derived from 
comint-mode).

>>> I won't argue what the default behavior should be, because it tends to
>>> become bike-shedding very fast.  FWIW, I use the default behavior,
>>> without customizing any scroll-related variables, and like that
>>> behavior, including in compilation buffers.
>>
>> Do you like the behavior of compilation buffer often having wasted
>> space, or do you just not mind it (with monitors being cheap and all)? I
>> don't see what anyone could really like about it.
>
> Very simple: I don't watch the compilation messages as they come in.
> It's a waste of time; I continue editing or doing something else while
> the compiler churns away.  To me, watching the messages is a relic
> from old DOS days when I couldn't do anything while waiting for the
> compiler to finish.
>
> I only look at the compiler messages when compilation finishes, and
> then I either scroll through the buffer or use "C-x `".  In both
> cases, what redisplay does when a new message comes in is of no
> interest to me.

I'm also only interested in what the window looks like when the 
compilation is finished. But I want to be able to see as much of the log 
as possible without scrolling or invoking any other commands.

I'm not compiling anything, actually, just calling rspec and looking at 
the output.

bug#13133: 24.2.90; scroll-conservatively is too coarse a setting

[Eli Zaretskii]

> Date: Tue, 11 Dec 2012 06:07:11 +0400
> From: Dmitry Gutov <dgutov@yandex.ru>
> CC: 13133@debbugs.gnu.org
> 
> On 10.12.2012 12:52, Eli Zaretskii wrote:
> >> Date: Mon, 10 Dec 2012 12:28:58 +0400
> >> From: Dmitry Gutov <dgutov@yandex.ru>
> >> CC: 13133@debbugs.gnu.org
> >>
> >> Like I mentioned, I don't want C-M-e/C-M-a to recenter. Why do you think
> >> it's TRT?
> >
> > Because you generally want to see the entire definition of the API,
> > not just the opening brace or paren.
> 
> Not sure if I understand you here. For example, if I'm in an Elisp 
> function, I can press C-M-a to go to its beginning, and the whole 
> definition (including arglist and docstring) will be visible. If the 
> value of scroll-conservatively is small, though, the function body may 
> be cut in half.
> Or do you specifically mean non-lisp languages where the docstring is 
> above the function definition?

Yes, the latter.

> >> As far as I'm concerned, recentering might be fine when we go to the end
> >> of a small function (it will fit on the screen anyway), but a larger
> >> function, which might have fit on the full screen, will be cut in half.
> >
> > IMO, C-M-e/C-M-a is not for observing the whole function.  You may be
> > looking for a separate feature, or maybe a modification of an existing
> > feature.
> 
> I don't think you can reasonably decide what they are for.

I didn't decide anything, I just gave you my interpretation.  That's
what "IMO" is for.

> > Can you cook up a test case?  I'd like to see why this happens.  (If
> > showing this requires injection of specific amount of text into the
> > compilation buffer, you could use 'cat' or some similar program to do
> > so, instead of actually running a compiler.)
> 
> Here's one:

Thanks, I'll take a look.