Resolving "cannot resolve rest collision: rest direction not set" warnings

[Arle Lommel]

Hi all, I am working on the same score that spawned discussion about stem lengths and now have another, hopefully less controversial, question.

I keep getting warnings like the following when I run Lilypond:

warning: cannot resolve rest collision: rest direction not set

They appear from snippets like this (reduced to a single example measure with two voices that are displayed single staff, although the original had five voices in three staves):

\parallelMusic #'(ornaments righthand) {

%006

\stemUp c''4\rest c8\rest \ottava #1 d'32[ a' d, a32] \ottava #0 c,8\rest d32[ a' d, a] |

r4 r4 <d fis>4 |

}

I understand that the issue is that the rests in the second voice (the two "r4" bits) and the ones in the first ("c''4\rest" and "c8\rest"  would occupy the same physical space (if I weren't already manually setting the location of the ones in the first voice), so the cause is clear. (If I were setting my own music this would be written so as to avoid the problem in the first place, but here I need to preserve the composer’s mode of _expression_.)

Since I am manually resolving the locations (and in fact want to do so in this case for other reasons), this is more of a question of curiosity than a problem, but how would one, in general, resolve this issue automatically? Is there a way to set the rest direction for each voice such that they would no longer clash? I've tried searching for answers to this issue and not found anything yet, although I'm sure someone will point me at something that (in hindsight) was obvious.

Best,

Arle