The following snippet:
\version "2.19.15"
staffSize = #(define-music-function (parser location new-size) (number?)
#{
\set fontSize = #new-size
\override StaffSymbol #'staff-space = #(magstep new-size)
\override StaffSymbol #'thickness = #(magstep new-size)
#})
Ab = \relative c' { f4 g a b }
\score {
\new Staff \with { \staffSize #2 { \Ab }
\layout { }
}
staffSize = #(define-music-function (parser location new-size) (number?)
#{
\set fontSize = #new-size
\override StaffSymbol #'staff-space = #(magstep new-size)
\override StaffSymbol #'thickness = #(magstep new-size)
#})
Ab = \relative c' { f4 g a b }
\score {
\new Staff \with { \staffSize #2 { \Ab }
\layout { }
}
produces at LP v2.19.15:
but at LP v2.19.16 produces:
Besides being wrong (see, e.g., "Behind Bars" by Elaine Gould, p.13), this causes many scores to require an additional page.
Applying convert-ly to the above snippet changes only the \version number.
I tried all values for new-size between -8 and +8; the only ones that failed were -4 and 2.
(The staffSize music-function was kindly contributed by Eluze in 2013 on this list to overcome limitations of layout-set-staff-size.)