Problem with merging whole measure rests

[David Wright]

There seems to be a problem in the merging whole measure rests
code. With 2.18.2, I'd been using the 336-based snippet from
https://raw.githubusercontent.com/wbsoft/lilymusic/master/include/merge-rests.ily
for some years, though I changed   0)   on the 110th line to   1)
in order to get the correct line on the staff: 2nd line down.

When run with 2.19.83, my modification is no longer necessary,
as it would hang the rests incorrectly from the top line.

Of course with 2.19.83 there's no need to use the 336-based snippet
at all, because Merge_rests_engraver is now built into LP. However,
as p180 of the NR shows in its score example, the rest now hangs
from the top line.

I imagine the error is somewhere after line 121 in
lilypond/usr/share/lilypond/current/scm/scheme-engravers.scm
but patching it looks more difficult than the old snippet.

Obviously 2.18 can't run the NR example, so I've attached some
files that demonstrate the old fix and the new manifestation.
IOW the first two should print correctly but the third prints
as in the NR.

Cheers,
David.

run-with-2.18.ly
Description: Text document

run-with-2.19.ly
Description: Text document

from-NR.ly
Description: Text document