Re: crash moving DotColumn

[Thomas Morley]

2016-05-12 15:51 GMT+02:00 David Kastrup <address@hidden>:
> Thomas Morley <address@hidden> writes:
>
>> To get more space between NoteColumn and DotColumn the following used
>> to work with 2.18.2
>>
>> foo =
>> \override Score.DotColumn.before-line-breaking =
>>   #(lambda (dot-column)
>>     (ly:grob-set-property! dot-column 'positioning-done
>>       (lambda (grob)
>>         (ly:dot-column::calc-positioning-done grob)
>>         (ly:grob-translate-axis! grob 15 X))))
>>
>>
>> {
>>   \foo
>>   <gis' a' c''>4.
>> }
>
> Stock 2.18.2 from Ubuntu:
>
> -*- mode: compilation; default-directory: "/tmp/" -*-
> Compilation started at Thu May 12 15:02:35
>
> /usr/bin/lilypond crash.ly
> GNU LilyPond 2.18.2
> Processing `crash.ly'
> Parsing...
> crash.ly:1: warning: no \version statement found, please add
>
> \version "2.18.2"
>
> for future compatibility
> Interpreting music...
> Preprocessing graphical objects...lilypond: grob-property.cc:248: 
> scm_unused_struct* Grob::try_callback_on_alist(scm_unused_struct**, SCM, 
> SCM): Assertion `value == ((SCM) ((((4)) << 8) + scm_tc8_flag)) || value == 
> marker' failed.
>
> Compilation aborted (core dumped) at Thu May 12 15:03:04
>
> Wow, they compiled with options enabling assertions.  In principle
> that's good, but I fear it might have been done using
> --disable-optimising.
>
>> With a build from latest master I get:
>>
>> lilypond: /home/hermann/lilypond-git/lily/grob-property.cc:242:
>> scm_unused_struct* Grob::try_callback_on_alist(scm_unused_struct**,
>> SCM, SCM): Assertion `scm_is_null (value) || scm_is_eq (value,
>> marker)' failed.
>> Aborted (core dumped)
>
> Ok, I might focus on the wrong things here...  But do you notice that
> the 2.18.2 assertion message at the top is much less readable because of
> being macro-expanded?
>
> That means that you are compiling with a rather current libc version.
> One that has already has my fix for this assertion message expansion
> issue.
>
>> A bug?
>
> It's not new, anyway.
>
>> How to do it different?
>
> Good question.  Wait.  When the call returned by a callback passed to
> try_callback_on_alist is *unspecified*, then the assertion checks that
> the original value is unset (or blocked by the current call).
> Otherwise, it _caches_ the callback value.
>
> The condition is rather obscure.  But the point appears to be that a
> callback should _never_ return *unspecified* since that messes with the
> caching.
>
> So probably your callback is missing a final #t.
>
> The assertion has been added with
>
> commit 635bff94c5a920d5866be4ff16751d771a35b7da
> Author: Han-Wen Nienhuys <address@hidden>
> Date:   Thu Jan 4 21:39:34 2007 +0100
>
>     allow callbacks on object values too. Init via meta field.
>
> However, the value checked by the assertion is fetched via
> internal_get_property rather than get_property_data (as it is now) in
> that commit.  This has been changed in
>
> commit a7646e7a00e1fe86e4f52123049f20fd28b48739
> Author: Han-Wen Nienhuys <address@hidden>
> Date:   Fri Jan 26 01:34:03 2007 +0100
>
>     check for calculation-in-progress marker in get_property().
>
> The problem we have after this commit is that get_property_data will
> return a procedure if the original entry was a callback (which it will
> be most of the time) and thus the assertion triggers.
>
> I am surprised we are not seeing this more often.  So at any rate, that
> assertion seems to be rather flaky.  We only reach it when a callback
> returns *unspecified*, though.
>
> I'm not sure what the expected behavior should be.
>
> --
> David Kastrup

Thanks a lot for your analysis and findings.

\version "2.19.42"

foo =
\override Score.DotColumn.before-line-breaking =
  #(lambda (dot-column)
    (ly:grob-set-property! dot-column 'positioning-done
      (lambda (grob)
        (ly:dot-column::calc-positioning-done grob)
        (ly:grob-translate-axis! grob 15 X)
        #t)))

{
  \foo
  <gis' a' c''>4.
}

Works indeed.
I could have sworn I tested this already...

Can't think about further implications right now, too tired.


Thanks,
  Harm