Issue 1192 in lilypond: System separators poorly spaced if systems include axis groups aliased to Staff

[lilypond]

Status: Started
Owner: n.puttock
Labels: Type-Collision Priority-High

New issue 1192 by n.puttock: System separators poorly spaced if systems  
include axis groups aliased to Staff
http://code.google.com/p/lilypond/issues/detail?id=1192

\version "2.13.29"

\header {
  texidoc = "
System separators are badly spaced if a system contains any axis
groups aliased to Staff (e.g., TabStaff, but also any
user-defined Staff-like context) since correct positioning of
system-separator-markup depends on the contexts defined in
verticallySpacedContexts.  This property is read by the
Vertically_aligned_context_engraver, which doesn't check for context
aliases when caching spaceable axis groups in the  
grob-array 'spaceable-staves.
"
}

\paper {
  ragged-right = ##t
  system-separator-markup = \slashSeparator
  annotate-spacing = ##t
}

<<
  \new DrumStaff {
    c'1 \break
    c'1
  }
  \new RhythmicStaff {
    c'1
    c'1
  }


There are no spaceable staves in the above snippet, which leads to the  
following error when translating the separator stencil:

programming error: Improbable offset for stencil: -nan staff space
Setting to zero.
continuing, cross fingers

Attachments:
        separator-bug.png  12.8 KB