ly:music-deep-copy and \relative

[Simon Albrecht]

Hello,

as Harm has pointed out, the following example gives unexpected (i.e. 
different) output:

\version "2.19"
repeat-note =
#(define-music-function (parser location music)(ly:music?)
  (make-sequential-music (list music (ly:music-deep-copy music))))

\absolute { c'1 \repeat-note c'' }
\relative c' { c \repeat-note c'1 }

There are several possible ways of handling this:
– Document it as a feature of ly:music-deep-copy in its search string. 
Users would have to circumvent it then.
– Modify ly:music-deep-copy to output both copies in the same octave. 
This would be most intuitive for what I think, since one would expect 
copies to be identical.
– Provide an optional (?) second argument to ly:music-deep-copy to 
choose between the two behaviours: abs-copy to use \relative only for 
determining the start of the first copy and start the second copy from 
the same absolute pitch; rel-copy to apply \relative also on the first 
note of the second copy (as in current behaviour).
– Use two dedicated functions for these two ways of handling it. What 
would they be named? I’d suggest ly:music-deep-copy-relative (current 
behaviour) and ly:music-deep-copy (new behaviour).

The third option would be easiest in terms of backward compatibility, 
the fourth is actually a variant of the second, with an additional 
possibility for convert-ly updating.

Yours, Simon