when nothing happens, buffer still marked as modified

when nothing happens, buffer still marked as modified

[Emanuel Berg]

Here [1] is a function I once wrote. My mind
isn't what it was back then, but testing it
with the different options (the `C-u' combos)
I understand it from a user's perspective and
it seems to do what it says.

Only one thing is missing what I can see, and
that is, when nothing happens (i e the piece of
text is already in the desired shape), the
buffer is still marked as modified (the `**')!

What is the correct way to prevent that?

(defun fill-down (start end &optional justify)
  "Fill the current paragraph from the current line down.\n
With mark active, act upon the region instead.\n
With \\[universal-argument] before invocation, JUSTIFY fully.
With \\[universal-argument] twice, remove full justification. (Or just fill it!)
With \\[universal-argument] thrice, center."
  (interactive
   (if (use-region-p)
       (list (region-beginning) (region-end) current-prefix-arg)
     (list (line-beginning-position)
           (save-excursion (forward-paragraph) (point))
           current-prefix-arg)))
  (if (equal justify '(16))  ; C-u C-u        -> unjustify
      (canonically-space-region start end)
    (fill-region
     start end
     (pcase justify
       (`(4)  'full)         ;    C-u         -> justify
       (`(64) 'center) ))))  ;    C-u C-u C-u -> center
                            ;; no C-u         -> none (i e just fill)

[1] http://user.it.uu.se/~embe8573/emacs-init/fill-new.el

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Re: when nothing happens, buffer still marked as modified

[Eli Zaretskii]

> From: Emanuel Berg <moasenwood@zoho.eu>
> Date: Wed, 05 Dec 2018 03:48:59 +0100
> 
> Only one thing is missing what I can see, and
> that is, when nothing happens (i e the piece of
> text is already in the desired shape), the
> buffer is still marked as modified (the `**')!
> 
> What is the correct way to prevent that?

Use with-silent-modifications, or just manually mark the buffer
unmodified using set-buffer-modified-p, when the function is about to
return.

Re: when nothing happens, buffer still marked as modified

[Emanuel Berg]

Eli Zaretskii wrote:

>> From: Emanuel Berg <moasenwood@zoho.eu> Date:
>> Wed, 05 Dec 2018 03:48:59 +0100
>> 
>> Only one thing is missing what I can see, and
>> that is, when nothing happens (i e the piece
>> of text is already in the desired shape), the
>> buffer is still marked as modified (the
>> `**')!
>> 
>> What is the correct way to prevent that?
>
> Use with-silent-modifications, or just manually
> mark the buffer unmodified using
> set-buffer-modified-p, when the function is
> about to return.

But how do I determine if the buffer has
changed or not? If it has, of course it should
be marked `**'!

-- 
underground experts united
http://user.it.uu.se/~embe8573

Re: when nothing happens, buffer still marked as modified

[Eli Zaretskii]

> From: Emanuel Berg <moasenwood@zoho.eu>
> Date: Wed, 05 Dec 2018 08:23:24 +0100
> 
> > Use with-silent-modifications, or just manually
> > mark the buffer unmodified using
> > set-buffer-modified-p, when the function is
> > about to return.
> 
> But how do I determine if the buffer has
> changed or not? If it has, of course it should
> be marked `**'!

That's the same problem that M-q has, and it leaves the modified
status intact.  Why not do as it does?

You could, of course, save a copy of the buffer before the changes,
and then compare, but why bother?

Re: when nothing happens, buffer still marked as modified

[Emanuel Berg]

Eli Zaretskii wrote:

>> But how do I determine if the buffer has
>> changed or not? If it has, of course it
>> should be marked `**'!
>
> That's the same problem that M-q has, and it
> leaves the modified status intact. Why not do
> as it does?

I'm not following, "Why not do as it does"?

> You could, of course, save a copy of the
> buffer before the changes, and then compare,
> but why bother?

Don't you think it is confusing, even
incorrect, to have the buffer change status
when the data hasn't changed from the command?

-- 
underground experts united
http://user.it.uu.se/~embe8573

Re: when nothing happens, buffer still marked as modified

[Eli Zaretskii]

> From: Emanuel Berg <moasenwood@zoho.eu>
> Date: Wed, 05 Dec 2018 11:09:24 +0100
> 
> Eli Zaretskii wrote:
> 
> >> But how do I determine if the buffer has
> >> changed or not? If it has, of course it
> >> should be marked `**'!
> >
> > That's the same problem that M-q has, and it
> > leaves the modified status intact. Why not do
> > as it does?
> 
> I'm not following, "Why not do as it does"?

I mean why not follow M-q's example?  It marks the buffer modified
even if re-filling the text arrived at the same text as before the
command.

> > You could, of course, save a copy of the
> > buffer before the changes, and then compare,
> > but why bother?
> 
> Don't you think it is confusing, even
> incorrect, to have the buffer change status
> when the data hasn't changed from the command?

The data did change, it just eventually arrived at the same contents.
Sheer luck.

Re: when nothing happens, buffer still marked as modified

[Michael Heerdegen]

Emanuel Berg <moasenwood@zoho.eu> writes:

> Don't you think it is confusing, even incorrect, to have the buffer
> change status when the data hasn't changed from the command?

See Bug#13949 and related.  AFAIR most people agreed that it would be
nice if Emacs behave differently in cases like yours, but it is an
absolutely non-trivial problem, and any solution wouldn't be extensive
and have downsides.

Michael.

Re: when nothing happens, buffer still marked as modified

[Amin Bandali]

On 2018-12-05 12:58 PM, Eli Zaretskii wrote:
> I mean why not follow M-q's example?  It marks the buffer modified
> even if re-filling the text arrived at the same text as before the
> command.

I’d noticed that in the past and found it strange.  Are there any
strong reasons for keeping the current behaviour vs. only marking
the buffer as modified when re-filling actually results in a
change?  Marking the buffer as modified when there was no visual
change seems like a ‘leaky abstraction’.

Though thinking about the wording (“modified”) more precisely, I
suppose the behaviour does technically make sense, but it still
feels somewhat strange / counter-intuitive.  I think it would be
nice to have a “difference” indicator for when an action results
in an actual difference compared to before.

Just my 2¢.

Re: when nothing happens, buffer still marked as modified

[Eli Zaretskii]

> From: Amin Bandali <bandali@gnu.org>
> Cc: help-gnu-emacs@gnu.org
> Date: Wed, 05 Dec 2018 08:39:49 -0500
> 
> On 2018-12-05 12:58 PM, Eli Zaretskii wrote:
> > I mean why not follow M-q's example?  It marks the buffer modified
> > even if re-filling the text arrived at the same text as before the
> > command.
> 
> I’d noticed that in the past and found it strange.  Are there any
> strong reasons for keeping the current behaviour vs. only marking
> the buffer as modified when re-filling actually results in a
> change?

The only strong reason is that it's not trivial to implement, and no
one has yet proposed a satisfactory patch to do that.

Re: when nothing happens, buffer still marked as modified

[Joost Kremers]

On Wed, Dec 05 2018, Eli Zaretskii wrote:
>> From: Emanuel Berg <moasenwood@zoho.eu>
>> Date: Wed, 05 Dec 2018 11:09:24 +0100
>> 
>> Eli Zaretskii wrote:
>> 
>> >> But how do I determine if the buffer has
>> >> changed or not? If it has, of course it
>> >> should be marked `**'!
>> >
>> > That's the same problem that M-q has, and it
>> > leaves the modified status intact. Why not do
>> > as it does?
>> 
>> I'm not following, "Why not do as it does"?
>
> I mean why not follow M-q's example?  It marks the buffer 
> modified
> even if re-filling the text arrived at the same text as before 
> the
> command.

Now I'm confused. The NEWS section for Emacs 26 says:

** 'fill-paragraph' no longer marks the buffer as changed unless 
   it
actually changed something.

Which seems to be implemented (correct me if I'm wrong, I only 
took a very quick look) by using `buffer-hash'. I thought that was 
what you meant when you said "do as it does"...


-- 
Joost Kremers
Life has its moments

Re: when nothing happens, buffer still marked as modified

[Eli Zaretskii]

> From: Joost Kremers <joostkremers@fastmail.fm>
> Date: Wed, 05 Dec 2018 16:00:15 +0100
> 
> Now I'm confused. The NEWS section for Emacs 26 says:
> 
> ** 'fill-paragraph' no longer marks the buffer as changed unless 
>    it
> actually changed something.
> 
> Which seems to be implemented (correct me if I'm wrong, I only 
> took a very quick look) by using `buffer-hash'. I thought that was 
> what you meant when you said "do as it does"...

I meant what it did before the change, but either way is a
possibility.

Re: when nothing happens, buffer still marked as modified

[Michael Heerdegen]

Joost Kremers <joostkremers@fastmail.fm> writes:

> ** 'fill-paragraph' no longer marks the buffer as changed unless it
> actually changed something.

Indeed.  But Emmanuel used `fill-region' which wasn't "fixed" in this
way, right?

Michael.

Re: when nothing happens, buffer still marked as modified

[Emanuel Berg]

Eli Zaretskii wrote:

>> Don't you think it is confusing, even
>> incorrect, to have the buffer change status
>> when the data hasn't changed from
>> the command?
>
> The data did change, it just eventually
> arrived at the same contents. Sheer luck.

I see. In a way that makes sense. If you hit
someone in the head with a bottle, but by sheer
luck do not inflict any physical or mental
damage whatsoever, it should still be
considered a crime. Put it up `**' in the
criminal record with my blessing!

-- 
underground experts united
http://user.it.uu.se/~embe8573

Re: when nothing happens, buffer still marked as modified

[Emanuel Berg]

Michael Heerdegen wrote:

>> ** 'fill-paragraph' no longer marks the
>> buffer as changed unless it actually
>> changed something.
>
> Indeed. But Emmanuel used `fill-region' which
> wasn't "fixed" in this way, right?

Either that, or my Emacs is too old:

    GNU Emacs 24.4.1 (arm-unknown-linux-gnueabihf,
    GTK+ Version 3.14.5) of 2017-09-13 on
    mb-lxc-01, modified by Debian

-- 
underground experts united
http://user.it.uu.se/~embe8573