Re: min-systems-per-page causes LilyPond to hang 2.20

[Jean Abou Samra]

Le 23/10/2020 à 11:18, Richard Shann a écrit :

> I'm afraid I wasn't perhaps clear enough in what I wrote: I was
> offering to remove large amounts of irrelevant material from the .ly
> file as it is machine-generated (by Denemo) and I understand what can
> be dropped without changing the music that LilyPond will try to
> typeset.
> However, even this is not an insignificant task and I'm not at all
> clear in what debugging scenario this would be useful. Normally when
> someone finds a crash asking them to chop down the file to isolate the
> bit causing the crash makes perfect sense. The file is hand-written and
> often chopping it down will reveal some typo or syntax combination
> which triggers the crash. In this case the same bits of syntax have
> been generated in thousands of files without trouble except for the
> introduction of min-systems-per-page  = 2 which is a new feature in
> Denemo. So it is highly likely that it is the combination of this
> syntax with \pageBreak that causes LilyPond to hang. It also means that
> altering any of the music that will actually be typeset is likely to
> trigger the disappearance/re-appearance of the bug - and indeed I found
> just this to be the case when I was first trying to track down the
> cause of the bug.
> So, if someone is wishing to tackle the debugging and needs irrelevant
> material to be removed from the exemplar for some specific reason I can
> help. But it would only reduce the file by about three quarters. I
> suspect debugging this would require detecting the loop that is being
> triggered and eyeballing the source code involved to see where it is
> being assumed that something will always break out of the loop. For
> that sort of work the input is irrelevant.
>
> Richard

Hello,

I opened https://gitlab.com/lilypond/lilypond/-/issues/6060

Note that I did reduce your file to a minimal example (didn't take
too long anyway), which revealed that LilyPond is not hanging on
an infinite loop but applying an extremely slow calculation which
should, nevertheless, terminate, at least in theory.

Best,
Jean