Help with page breaking code

[David Kastrup]

Hi,
the following code produces 9 pages in current master:

#(set! empty-stencil (ly:make-stencil '() empty-interval empty-interval))
\markup \fill-line { }
\markup { }
\markup { }
\markup { }
\markup { }
\markup { }
\markup { }
\markup { }
\markup { }

Basically, the first \markup produces an empty stencil with extents
(+inf.0 . -inf.0) and the page breaking code goes bonkers on that.
Since the current spacing code in issue 3330 requires this
representation for empty stencil extents, I can't really commit in this
state.

As a corollary: if extent (+inf.0 . -inf.0) throws the page breaking
code completely off-track in this case, it is unlikely that the
_current_ extent (+1.0 . -1.0) for empty stencils produces a _correct_
result either.  It will just be less noticeably wrong.

Anybody have an idea where or how to look?

-- 
David Kastrup