Re: spacing-spanner: rods for non-adjacent paper-columns; issue 1700 (issue 6489107)

[k-ohara5a5a]

http://codereview.appspot.com/6489107/diff/9001/lily/spacing-spanner.cc
File lily/spacing-spanner.cc (left):

http://codereview.appspot.com/6489107/diff/9001/lily/spacing-spanner.cc#oldcode274
lily/spacing-spanner.cc:274: doesn't touch the right column. */
This comment tells me what the code did, but not why.
When setting spacing constraints for a column on the right, it was
checking columns to the left until they were too far to matter, then
checking the line-broken version of one column farther back to the
left.

This could matter for cases where the broken version (likely a clef and
key signature) interleaves more with intervening note-columns that the
unbroken version (likely a barline).  The simplest example I can think
of is

\paper{ragged-right = ##t }
music = {
  \grace { \stemDown <b,-1-2-3>8[ c d] }
  <e'-1-2-3-4-5>4 r2.}
\new PianoStaff \with {
  fingeringOrientations = #'(left)
} <<
  \new Staff{\clef alto R1 \music \break \music}
  \new Staff{\clef alto R1 R1*2 }


Maybe more relevant cases come up in medieval music?

http://codereview.appspot.com/6489107/