Re: engraving ends too early

[David Kastrup]

Dan Eble <address@hidden> writes:

> % 2.19.20 does not engrave the lyrics and stops engraving the vocal
> % staff before the end.  (Compare to 2.18.2.)  I haven’t tested MIDI.
>
> \version "2.18.0"
> \include "english.ly"
>
> vocal = \relative c'' { R1 | f2 c }
>
> % adding the skip makes 2.19.20 work
> accomp = \relative c'' { c1 %{ s1 %} }
>
> \score {
>   <<
>     <<      
>       \new Staff <<
>       \new Voice = "vocal" { \vocal }
>       >>
>       \new Lyrics <<
>       \lyricsto "vocal" { \lyricmode { La la } }
>       >>
>     >>
>     
>     \new Staff <<
>       \context Voice = "obligII" { \accomp }
>     >>
>   >>
> }

MIDI will be the same: this is an iterator issue so all outputs will be
affected similarly.

This is obviously a consequence of the fix for issue 2010 (and 702 and
1551).  This fix is a rather heavy-handed one.  The problems it cures
are arguably weirder and harder to work around than the stuff that now
terminates early: the original problem was tied to stuff sticking around
for too long even when it terminated at the same time as something else,
while the current problem is stuff terminating early along with other
stuff.

I've spent several weeks on this one and have not been able to find a
nicer fix.  That does not mean that there isn't one: I did not really
figure out the real cause of the problem to my satisfaction.

There are several elements involved, my guess is the following:
a) the first context in a group of << ... >> is kept alive while the
rest still has action.
b) there are situations where a context is kept alive with the only
remaining "action" in his group is an associated Lyrics context that has
not registered the nominal death of its associated context which in turn
is artificially alive until the Lyrics in the group die.

Now the current fix relies on the associated lyrics and the controlling
context being in the same << ... >> construct.  Clearly that
assumption/requirement is not met too often for comfort.

-- 
David Kastrup