Not nice but works:
%%% SNIPPET BEGINS
\version "2.19.83"
\include "arrows.ily"
#(define-markup-command (arrow-at-angle layout props angle-deg) (number?)
(let* ((PI-OVER-180 (/ (atan 1 1) 34))
(degrees->radians (lambda (degrees) (* degrees PI-OVER-180)))
(angle-rad (degrees->radians angle-deg))
(target-x (* 3 (cos angle-rad)))
(target-y (* 3 (sin angle-rad))))
(interpret-markup layout props
(markup
#:translate (cons (/ target-x 2.1) (/ target-y 2.1))
#:rotate angle-deg
#:arrow "closed" #f 0 1 3.5 .1))))
testingMusic = {
c'1
\once \override Staff.BarLine.stencil =
#(lambda (grob)
(ly:stencil-combine-at-edge
(ly:bar-line::print grob)
X RIGHT
(grob-interpret-markup grob
#{
\markup\with-dimensions-from\null {
\translate #'(5 . 0)
\combine
\arrow-at-angle #-30
\arrow-at-angle #30
}
#})
0))
\break
\time 3/4 c'2.
\once \override Staff.BarLine.stencil =
#(lambda (grob)
(ly:stencil-combine-at-edge
(ly:bar-line::print grob)
X RIGHT
(grob-interpret-markup grob
#{
\markup\with-dimensions-from\null {
\translate #'(8.2 . 0)
\combine
\arrow-at-angle #-30
\arrow-at-angle #30
}
#})
0))
\break
\key bes \major \time 4/4 c'1
\once \override Staff.BarLine.stencil =
#(lambda (grob)
(ly:stencil-combine-at-edge
(ly:bar-line::print grob)
X RIGHT
(grob-interpret-markup grob
#{
\markup\with-dimensions-from\null {
\translate #'(8.8 . 0)
\combine
\arrow-at-angle #-30
\arrow-at-angle #30
}
#})
0))
\break
\key a \major c'1
}
\score {
\new Staff \testingMusic
}
%%% SNIPPET ENDS
HTH, Cheers,
Pierre