Question about align-to behaviour with wrap-mode

Question about align-to behaviour with wrap-mode

[Abdul-Lateef Haji-Ali via Users list for the GNU Emacs text editor]

I noticed what I think is strange behaviour with `:align-to` that I am wondering if it's intended and if there's a way of achieving a desired behaviour.

To reproduce in an `emacs -Q`, just run this:

(progn
   (toggle-word-wrap +1)
   (goto-char (point-max))
   (insert
    (concat "\n\n"
            (make-string (- (window-width) 3) 69)
            " "
            (propertize " " 'display
                        `(space :align-to (- right
                                             10)))
            "After\n\n")))

The word 'After' is not aligned to `(- right 10)` because the text before is too long. Instead "After" is displayed at the beginning of the next line (or broken across two lines if toggle-word-wrap is disabled) and the alignment is ignored.

If I execute instead

(progn
   (toggle-word-wrap +1)
   (goto-char (point-max))
   (insert
    (concat "\n\n"
            (make-string (window-width) 69)
            " "
            (propertize " " 'cursor 1 'display
                        `(space :align-to (- right
                                             10)))
            "After\n\n")))
            
the alignment is "correct" on the second line.

In both situation, I was intending (and expecting) the word "After" to be on the second line and to be correctly aligned at (- right 10). Is the current behaviour intended? Is there a way to achieve my desired behaviour?

I could of course add spaces before the right-aligned text, but then if more text is added I would need to adjust the spaces dynamically which is less-than-ideal.

-- Al

________________________________
Heriot-Watt University was founded in 1821 and is a registered Scottish charity (SC000278).

Re: Question about align-to behaviour with wrap-mode

[Eli Zaretskii]

> Date: Sun, 20 Nov 2022 22:20:50 +0000
> From:  Abdul-Lateef Haji-Ali via Users list for the GNU Emacs text editor <help-gnu-emacs@gnu.org>
> 
> 
> I noticed what I think is strange behaviour with `:align-to` that I am wondering if it's intended and if there's a way of achieving a desired behaviour.

It's intended, yes.

> To reproduce in an `emacs -Q`, just run this:
> 
> (progn
>    (toggle-word-wrap +1)
>    (goto-char (point-max))
>    (insert
>     (concat "\n\n"
>             (make-string (- (window-width) 3) 69)
>             " "
>             (propertize " " 'display
>                         `(space :align-to (- right
>                                              10)))
>             "After\n\n")))
> 
> The word 'After' is not aligned to `(- right 10)` because the text before is too long. Instead "After" is displayed at the beginning of the next line (or broken across two lines if toggle-word-wrap is disabled) and the alignment is ignored.
> 
> If I execute instead
> 
> (progn
>    (toggle-word-wrap +1)
>    (goto-char (point-max))
>    (insert
>     (concat "\n\n"
>             (make-string (window-width) 69)
>             " "
>             (propertize " " 'cursor 1 'display
>                         `(space :align-to (- right
>                                              10)))
>             "After\n\n")))
>             
> the alignment is "correct" on the second line.

I don't see the correct alignment here.  I see a behavior similar to the
first recipe, as I'd expect.

The problem here is that the implementation of align-to takes the width of
continuation lines into consideration, i.e. the column doesn't wrap to zero
when the line is continued.  So if the window is 80-column wide, and you say

     (space :align-to (- right 10))

that yields 70, but text wrapped to the next line has its horizontal
coordinate start from 80, so it is already past 70, and the alignment
doesn't happen.

The bottom line is that you cannot use relative alignment if your lines can
wrap, and hope for that to work.  For wrapped lines the alignment must be to
absolute column numbers, and it must take the continuation lines into
consideration when you calculate the alignment column.

Re: Question about align-to behaviour with wrap-mode

[Abdul-Lateef Haji-Ali via Users list for the GNU Emacs text editor]

Thanks Eli for explaining.

> I don't see the correct alignment here.  I see a behavior similar to the
> first recipe, as I'd expect.

This is what I see with this example on my Emacs 28.2 (assume window width is 50):

,----
| EEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE
|                                         After
`----

So the text is "correctly" aligned to (- right 10) on the second line. Are you seeing something different?

The only problem I see is that when the word is broken and word-wrap is off then I get

,----
| EEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE Af
| ter                                      
`----

while if word wrap is on I get

,----
| EEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE
| After                                      
`----


> The bottom line is that you cannot use relative alignment if your lines can
> wrap, and hope for that to work.  For wrapped lines the alignment must be to
> absolute column numbers, and it must take the continuation lines into
> consideration when you calculate the alignment column.

I see. Do you mean that I should write a hook to update the alignment of "After" as more text is inserted before it (to calculate the alignment column taking the continuation lines into considerations)?
Or is there a way to have `align-to` be calculated from a function?

Thanks,
-- Al

________________________________
Heriot-Watt University was founded in 1821 and is a registered Scottish charity (SC000278).

Re: Question about align-to behaviour with wrap-mode

[Eli Zaretskii]

> From: Abdul-Lateef Haji-Ali <a.hajiali@hw.ac.uk>
> Date: Tue, 22 Nov 2022 09:45:20 +0000
> 
> > The bottom line is that you cannot use relative alignment if your lines can
> > wrap, and hope for that to work.  For wrapped lines the alignment must be to
> > absolute column numbers, and it must take the continuation lines into
> > consideration when you calculate the alignment column.
> 
> I see. Do you mean that I should write a hook to update the alignment of "After" as more text is inserted before it (to calculate the alignment column taking the continuation lines into considerations)?

Yes, something like that.

Basically, align-to is not well suited to deal with continued lines.