bug#23809: 24.5; Positive argument to 'posn-at-point' throws erros as being negative

bug#23809: 24.5; Positive argument to 'posn-at-point' throws erros as being negative

[Lluís Vilanova]

To reproduce:

* Open a PDF on a separate window on the same frame using pdf-tools.
* Select that window.
* Scroll a bit down the first page of the PDF.
* Use windmove to move from the pdf-view-mode buffer to the first one.


With these steps, I get this backtrace:

  Debugger entered--Lisp error: (wrong-type-argument wholenump -14)
    posn-at-point(619194 #)
    (nth 2 (posn-at-point (window-point window) window))
    (let ((posn-cons (nth 2 (posn-at-point (window-point window) window)))) (if hor (+ (or (cdr posn-cons) 1) (window-pixel-top window)) (+ (or (car posn-cons) 1) (window-pixel-left window))))
    (cond ((and (numberp sign) (< sign 0)) (if hor (1- (+ (window-pixel-top window) (window-pixel-height window))) (1- (+ (window-pixel-left window) (window-pixel-width window))))) ((and (numberp sign) (> sign 0)) (if hor (window-pixel-top window) (window-pixel-left window))) ((let ((posn-cons (nth 2 (posn-at-point (window-point window) window)))) (if hor (+ (or (cdr posn-cons) 1) (window-pixel-top window)) (+ (or (car posn-cons) 1) (window-pixel-left window))))))
    (let* ((frame (window-frame window)) (hor (memq direction (quote (left right)))) (first (if hor (window-pixel-left window) (window-pixel-top window))) (last (+ first (window-size window hor t))) (posn (cond ((and (numberp sign) (< sign 0)) (if hor (1- (+ ... ...)) (1- (+ ... ...)))) ((and (numberp sign) (> sign 0)) (if hor (window-pixel-top window) (window-pixel-left window))) ((let ((posn-cons ...)) (if hor (+ ... ...) (+ ... ...)))))) (best-edge (cond ((eq direction (quote below)) (frame-pixel-height frame)) ((eq direction (quote right)) (frame-pixel-width frame)) (t -1))) (best-edge-2 best-edge) (best-diff-2 (if hor (frame-pixel-height frame) (frame-pixel-width frame))) best best-2 best-diff-2-new) (walk-window-tree (function (lambda (w) (let* ((w-top (window-pixel-top w)) (w-left (window-pixel-left w))) (cond ((or ... ...)) (hor (cond ... ...)) ((and ... ...) (if ... ...)) ((and ... ... ...) (setq best-edge-2 w-top) (setq best-diff-2 best-diff-2-new) (setq best-2 w)))))) frame nil (and mini t)) (or best best-2))
    window-in-direction(left nil nil nil nil t)
    windmove-find-other-window(left nil nil)
    windmove-do-window-select(left nil)
    windmove-left(nil)
    #(windmove-left nil nil)
    ad-Advice-call-interactively(# windmove-left nil nil)
    apply(ad-Advice-call-interactively # (windmove-left nil nil))
    call-interactively(windmove-left nil nil)
    command-execute(windmove-left)


Note how the argument to posn-at-point (returned by window-point) is actually
positive (619194), but the error raised by Emacs complains about the number
being negative (-14).

Thanks,
  Lluis


Auto-gathered information:

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bug#23809: 24.5; Positive argument to 'posn-at-point' throws erros as being negative

[Eli Zaretskii]

> From: Lluís Vilanova <vilanova@ac.upc.edu>
> Date: Mon, 20 Jun 2016 18:30:51 +0200
> 
> To reproduce:
> 
> * Open a PDF on a separate window on the same frame using pdf-tools.
> * Select that window.
> * Scroll a bit down the first page of the PDF.
> * Use windmove to move from the pdf-view-mode buffer to the first one.

Sounds like a duplicate of bug #21732.

> With these steps, I get this backtrace:
> 
>   Debugger entered--Lisp error: (wrong-type-argument wholenump -14)
>     posn-at-point(619194 #)

What does pos-visible-in-window-p return for that buffer position?

> Note how the argument to posn-at-point (returned by window-point) is actually
> positive (619194), but the error raised by Emacs complains about the number
> being negative (-14).

That's not relevant: 619194 is a buffer position, whereas -14 is the
y-coordinate (in pixels) passed by posn-at-point to posn-at-x-y.  The
latter cannot cope with negative y coordinates, for reasons that
should be obvious.

The question is how that -14 coordinate came into existence.  If you
can step with a debugger into Fpos_visible_in_window_p, and see what's
going on there, that would be helpful.  (I cannot try that myself, as
my systems don't support pdf-view-mode.)

Thanks.

bug#23809: 24.5; Positive argument to 'posn-at-point' throws erros as being negative

[martin rudalics]

[-- Attachment #1: Type: text/plain, Size: 292 bytes --]

 > Sounds like a duplicate of bug #21732.
 >
 >> With these steps, I get this backtrace:
 >>
 >>    Debugger entered--Lisp error: (wrong-type-argument wholenump -14)
 >>      posn-at-point(619194 #)

Without further forensics we could "fix" both bugs using the attached
patch.  WDYT?

martin

[-- Attachment #2: window.diff --]
[-- Type: text/plain, Size: 631 bytes --]

diff --git a/lisp/window.el b/lisp/window.el
index f7a547b..a06f334 100644
--- a/lisp/window.el
+++ b/lisp/window.el
@@ -2068,7 +2068,9 @@ window-in-direction
 	    (if hor
 		(window-pixel-top window)
 	      (window-pixel-left window)))
-	   ((let ((posn-cons (nth 2 (posn-at-point (window-point window) window))))
+	   ((let ((posn-cons (condition-case nil
+                                 (nth 2 (posn-at-point (window-point window) window))
+                               (error nil))))
 	      (if hor
 		  (+ (or (cdr posn-cons) 1) (window-pixel-top window))
 		(+ (or (car posn-cons) 1) (window-pixel-left window)))))))

bug#23809: 24.5; Positive argument to 'posn-at-point' throws erros as being negative

[Lluís Vilanova]

Eli Zaretskii writes:

>> From: Lluís Vilanova <vilanova@ac.upc.edu>
>> Date: Mon, 20 Jun 2016 18:30:51 +0200
>> 
>> To reproduce:
>> 
>> * Open a PDF on a separate window on the same frame using pdf-tools.
>> * Select that window.
>> * Scroll a bit down the first page of the PDF.
>> * Use windmove to move from the pdf-view-mode buffer to the first one.

> Sounds like a duplicate of bug #21732.

>> With these steps, I get this backtrace:
>> 
>> Debugger entered--Lisp error: (wrong-type-argument wholenump -14)
>> posn-at-point(619194 #)

> What does pos-visible-in-window-p return for that buffer position?

If I evaluate it after the error (when in the Backtrace buffer), I get nil
(pos-visible-in-window-p (window-point window) window). Using gdb it's a
different value (see below).


>> Note how the argument to posn-at-point (returned by window-point) is actually
>> positive (619194), but the error raised by Emacs complains about the number
>> being negative (-14).

> That's not relevant: 619194 is a buffer position, whereas -14 is the
> y-coordinate (in pixels) passed by posn-at-point to posn-at-x-y.  The
> latter cannot cope with negative y coordinates, for reasons that
> should be obvious.

> The question is how that -14 coordinate came into existence.  If you
> can step with a debugger into Fpos_visible_in_window_p, and see what's
> going on there, that would be helpful.  (I cannot try that myself, as
> my systems don't support pdf-view-mode.)

I have zero knowledge on Emacs' source code, but here's the little information I
could gather:

  Fposn_at_point(...)
    Fvisible_in_window_p(...) -> (824 . -98)
      pos_visible_p(...) ->
        line 1713 : *x = it2.current_x;
        value            824
        line 1714 : *y = it2.current_y + it2.max_ascent - it2.ascent;
        value            -98             533              533
    Fposn_at_x_y(824, -98, window, nil)

After reading [1], it sounds to me that pdf-tools (and doc-view) let you scroll
the buffer, but never move point. That could be a reason to get a negative
position AFAIU.

Tell me if you want something more specific, since the problem is pretty easy to
reproduce. But remember I have zero knowledge on emacs' sources, some I'm pretty
blind here.


[1] https://debbugs.gnu.org/cgi/bugreport.cgi?bug=21732#8

Thanks,
  Lluis

bug#23809: 24.5; Positive argument to 'posn-at-point' throws erros as being negative

[Eli Zaretskii]

> Date: Tue, 21 Jun 2016 15:07:57 +0200
> From: martin rudalics <rudalics@gmx.at>
> CC: 23809@debbugs.gnu.org
> 
>  > Sounds like a duplicate of bug #21732.
>  >
>  >> With these steps, I get this backtrace:
>  >>
>  >>    Debugger entered--Lisp error: (wrong-type-argument wholenump -14)
>  >>      posn-at-point(619194 #)
> 
> Without further forensics we could "fix" both bugs using the attached
> patch.  WDYT?

I don't like sweeping problems under the carpet.  We should understand
how come we get negative pixel coordinates in these cases, it's most
likely some bug in pos_visible_p or somesuch.

bug#23809: 24.5; Positive argument to 'posn-at-point' throws erros as being negative

[martin rudalics]

 > I don't like sweeping problems under the carpet.  We should understand
 > how come we get negative pixel coordinates in these cases, it's most
 > likely some bug in pos_visible_p or somesuch.

A ‘condition-case’ would fix the problem on the release branch and give
you all the time to find the real cause.  Also, unless we guard against
‘posn-at-point’ ever returning a negative y-value, there's no guarantee
that finding the cause of the present problem will fix this issue once
and for all.

martin

bug#23809: 24.5; Positive argument to 'posn-at-point' throws erros as being negative

[Eli Zaretskii]

> Date: Wed, 22 Jun 2016 08:10:44 +0200
> From: martin rudalics <rudalics@gmx.at>
> CC: vilanova@ac.upc.edu, 23809@debbugs.gnu.org
> 
>  > I don't like sweeping problems under the carpet.  We should understand
>  > how come we get negative pixel coordinates in these cases, it's most
>  > likely some bug in pos_visible_p or somesuch.
> 
> A ‘condition-case’ would fix the problem on the release branch and give
> you all the time to find the real cause.

the problem doesn't seem grave enough to rush with a solution.

> Also, unless we guard against ‘posn-at-point’ ever returning a
> negative y-value, there's no guarantee that finding the cause of the
> present problem will fix this issue once and for all.

We will cross that bridge when we get to it.

Thanks.

bug#23809: 24.5; Positive argument to 'posn-at-point' throws erros as being negative

[Eli Zaretskii]

> From: Lluís Vilanova <vilanova@ac.upc.edu>
> Cc: 23809@debbugs.gnu.org
> Date: Tue, 21 Jun 2016 15:17:46 +0200
> 
> > The question is how that -14 coordinate came into existence.  If you
> > can step with a debugger into Fpos_visible_in_window_p, and see what's
> > going on there, that would be helpful.  (I cannot try that myself, as
> > my systems don't support pdf-view-mode.)
> 
> I have zero knowledge on Emacs' source code, but here's the little information I
> could gather:
> 
>   Fposn_at_point(...)
>     Fvisible_in_window_p(...) -> (824 . -98)
>       pos_visible_p(...) ->
>         line 1713 : *x = it2.current_x;
>         value            824
>         line 1714 : *y = it2.current_y + it2.max_ascent - it2.ascent;
>         value            -98             533              533
>     Fposn_at_x_y(824, -98, window, nil)
> 
> After reading [1], it sounds to me that pdf-tools (and doc-view) let you scroll
> the buffer, but never move point. That could be a reason to get a negative
> position AFAIU.
> 
> Tell me if you want something more specific, since the problem is pretty easy to
> reproduce. But remember I have zero knowledge on emacs' sources, some I'm pretty
> blind here.

Thanks, the above is already a lot of valuable info.

I have a couple of follow up questions:

  . Can you show the entire value returned by Fpos_visible_in_window_p
    when its call from Fposn_at_point returns, when this problem is
    reproduced?  If you load the file .gdbinit that is located in the
    Emacs src directory, then displaying the return value is simple:
    type "pp tem" at the GDB prompt, after Fpos_visible_in_window_p
    returns.

  . You say "pdf-tools (and doc-view) let you scroll the buffer, but
    never move point" -- can you point me to code in pdf-tools that
    does this?

Thanks.

bug#23809: 24.5; Positive argument to 'posn-at-point' throws erros as being negative

[Lluís Vilanova]

Eli Zaretskii writes:

>> From: Lluís Vilanova <vilanova@ac.upc.edu>
>> Cc: 23809@debbugs.gnu.org
>> Date: Tue, 21 Jun 2016 15:17:46 +0200
>> 
>> > The question is how that -14 coordinate came into existence.  If you
>> > can step with a debugger into Fpos_visible_in_window_p, and see what's
>> > going on there, that would be helpful.  (I cannot try that myself, as
>> > my systems don't support pdf-view-mode.)
>> 
>> I have zero knowledge on Emacs' source code, but here's the little information I
>> could gather:
>> 
>> Fposn_at_point(...)
>> Fvisible_in_window_p(...) -> (824 . -98)
>> pos_visible_p(...) ->
>> line 1713 : *x = it2.current_x;
>> value            824
>> line 1714 : *y = it2.current_y + it2.max_ascent - it2.ascent;
>> value            -98             533              533
>> Fposn_at_x_y(824, -98, window, nil)
>> 
>> After reading [1], it sounds to me that pdf-tools (and doc-view) let you scroll
>> the buffer, but never move point. That could be a reason to get a negative
>> position AFAIU.
>> 
>> Tell me if you want something more specific, since the problem is pretty easy to
>> reproduce. But remember I have zero knowledge on emacs' sources, some I'm pretty
>> blind here.

> Thanks, the above is already a lot of valuable info.

> I have a couple of follow up questions:

>   . Can you show the entire value returned by Fpos_visible_in_window_p
>     when its call from Fposn_at_point returns, when this problem is
>     reproduced?  If you load the file .gdbinit that is located in the
>     Emacs src directory, then displaying the return value is simple:
>     type "pp tem" at the GDB prompt, after Fpos_visible_in_window_p
>     returns.

Sorry, but strangely enough, I'm unable to reproduce the problem now. And I'm
not aware of having updated emacs nor the packages it uses. I'll reply with the
information if it happens again.


>   . You say "pdf-tools (and doc-view) let you scroll the buffer, but
>     never move point" -- can you point me to code in pdf-tools that
>     does this?

I'm actually not sure about it. It's just an intuition based on the fact that
the keys used to move point actually scroll the window, and there is no visible
point in it.


Thanks,
  Lluis

bug#23809: 24.5; Positive argument to 'posn-at-point' throws erros as being negative

[Eli Zaretskii]

> From: Lluís Vilanova <vilanova@ac.upc.edu>
> Cc: 23809@debbugs.gnu.org
> Date: Mon, 11 Jul 2016 12:23:15 +0200
> 
> >   . Can you show the entire value returned by Fpos_visible_in_window_p
> >     when its call from Fposn_at_point returns, when this problem is
> >     reproduced?  If you load the file .gdbinit that is located in the
> >     Emacs src directory, then displaying the return value is simple:
> >     type "pp tem" at the GDB prompt, after Fpos_visible_in_window_p
> >     returns.
> 
> Sorry, but strangely enough, I'm unable to reproduce the problem now. And I'm
> not aware of having updated emacs nor the packages it uses. I'll reply with the
> information if it happens again.

Strange indeed.  Thanks in advance.

> >   . You say "pdf-tools (and doc-view) let you scroll the buffer, but
> >     never move point" -- can you point me to code in pdf-tools that
> >     does this?
> 
> I'm actually not sure about it. It's just an intuition based on the fact that
> the keys used to move point actually scroll the window, and there is no visible
> point in it.

That sounds like the normal image scrolling feature of Emacs.
The reason I asked is that I tried to reproduce the problem by
scrolling through a very large image, but couldn't.  So there's some
other factor at work here that I cannot grasp.