\version "2.19.36"

#(define stemlet-length-to-rest
;; Always extend stemlets over beamed rests, minimum is 0.5
  (lambda (grob) 
    (let* ((stem (ly:grob-object grob 'stem))
           (beam 
             (if stem
                 (ly:grob-object stem 'beam)
                 #f)))
      (if (and (not (null? beam)) (not (null? stem)))
          (let* ((sys 
                   (ly:grob-system grob))
                 (stems 
                   (ly:grob-array->list (ly:grob-object beam 'stems)))
                 (stem-coord
                   (- (ly:grob-relative-coordinate 
                        (car (member stem stems)) sys X)
                      (ly:grob-relative-coordinate 
                        (car stems) sys X)))
                 (beam-pos
                   (ly:grob-property beam 'positions))
                 (beam-y-length
                   (- (car beam-pos) (cdr beam-pos)))
                 (beam-x-length
                   (let ((x-pos (ly:grob-property beam 'X-positions)))
                     (- (car x-pos) (cdr x-pos))))
                 (stem-add-for-beam-slant
                   (if (or (inf? stem-coord) (zero? stem-coord))
                       0
                       (* (/ beam-y-length beam-x-length)
                          stem-coord)))
                 (beam-dir
                   (ly:grob-property beam 'direction))
                 (staff-space 
                   (ly:staff-symbol-staff-space grob))
                 (rest-y-ext
                   (ly:grob-extent grob (ly:grob-parent grob Y) Y)))
            (ly:grob-set-property! stem 'stemlet-length 
              (max 0.5
                (+ (* beam-dir stem-add-for-beam-slant)
                   (- (if (= beam-dir DOWN)
                          (- (car rest-y-ext) (car beam-pos)) 
                          (- (car beam-pos) (cdr rest-y-ext)))
                      (/ staff-space 2))))))))))
	  
stemlets-test =
  \override Rest.after-line-breaking = #stemlet-length-to-rest

m = { r8[ d''\rest r c''8] c''2 \bar "||" }
mus = {
  \time 2/4
  \voiceOne
  \m
  \once \override Beam.positions = #'(5 . 7)
  \m
  \once \override Beam.positions = #'(7 . 5)
  \m
  \voiceTwo
  \m
  \once \override Beam.positions = #'(-5 . -7)
  \m
  \once \override Beam.positions = #'(-7 . -5)
  \m
}

\score {
  \new StaffGroup
    <<
      \new Staff \mus
      \new Staff \mus
    >>
  \layout {
    \stemlets-test
  }
}