\version "2.19.15"

%% => http://lists.gnu.org/archive/html/lilypond-user/2014-10/msg00446.html
%% => http://lsr.di.unimi.it/LSR/Item?id=954

#(define (test-stencil grob text)
   (let* ((orig (ly:grob-original grob))
          (siblings (ly:spanner-broken-into orig)) ; have we been split?
          (refp (ly:grob-system grob))
          (left-bound (ly:spanner-bound grob LEFT))
          (right-bound (ly:spanner-bound grob RIGHT))
          (elts-L (ly:grob-array->list (ly:grob-object left-bound 'elements)))
          (elts-R (ly:grob-array->list (ly:grob-object right-bound 'elements)))
          (break-alignment-L
           (filter
            (lambda (elt) (grob::has-interface elt 'break-alignment-interface))
            elts-L))
          (break-alignment-R
           (filter
            (lambda (elt) (grob::has-interface elt 'break-alignment-interface))
            elts-R))
          (break-alignment-L-ext (ly:grob-extent (car break-alignment-L) refp X))
          (break-alignment-R-ext (ly:grob-extent (car break-alignment-R) refp X))
          (num
           (markup text))
          (num
           (if (or (null? siblings)
                   (eq? grob (car siblings)))
               num
               (make-parenthesize-markup num)))
          (num (grob-interpret-markup grob num))
          (num-stil-ext-X (ly:stencil-extent num X))
          (num-stil-ext-Y (ly:stencil-extent num Y))
          (num (ly:stencil-aligned-to num X CENTER))
          (num
           (ly:stencil-translate-axis
            num
            (+ (interval-length break-alignment-L-ext)
              (* 0.5
                (- (car break-alignment-R-ext)
                  (cdr break-alignment-L-ext))))
            X))
          (bracket-L
           (markup
            #:path
            0.1 ; line-thickness
            `((moveto 0.5 ,(* 0.5 (interval-length num-stil-ext-Y)))
              (lineto ,(* 0.5
                         (- (car break-alignment-R-ext)
                           (cdr break-alignment-L-ext)
                           (interval-length num-stil-ext-X)))
                ,(* 0.5 (interval-length num-stil-ext-Y)))
              (closepath)
              (rlineto 0.0
                ,(if (or (null? siblings) (eq? grob (car siblings)))
                     -1.0 0.0)))))
          (bracket-R
           (markup
            #:path
            0.1
            `((moveto ,(* 0.5
                         (- (car break-alignment-R-ext)
                           (cdr break-alignment-L-ext)
                           (interval-length num-stil-ext-X)))
                ,(* 0.5 (interval-length num-stil-ext-Y)))
              (lineto 0.5
                ,(* 0.5 (interval-length num-stil-ext-Y)))
              (closepath)
              (rlineto 0.0
                ,(if (or (null? siblings) (eq? grob (last siblings)))
                     -1.0 0.0)))))
          (bracket-L (grob-interpret-markup grob bracket-L))
          (bracket-R (grob-interpret-markup grob bracket-R))
          (num (ly:stencil-combine-at-edge num X LEFT bracket-L 0.4))
          (num (ly:stencil-combine-at-edge num X RIGHT bracket-R 0.4)))
     num))

#(define (add-bound-item spanner item)
   (if (null? (ly:spanner-bound spanner LEFT))
       (ly:spanner-set-bound! spanner LEFT item)
       (ly:spanner-set-bound! spanner RIGHT item)))

#(define-public (Measure_attached_spanner_engraver context)
   (let ((span '())
         (finished '())
         (event-start '())
         (event-stop '()))
     (make-engraver
      (listeners ((measure-counter-event engraver event)
                  (if (= START (ly:event-property event 'span-direction))
                      (set! event-start event)
                      (set! event-stop event))))
      ((process-music trans)
       (if (ly:stream-event? event-stop)
           (if (null? span)
               (ly:warning "You're trying to end a measure-attached spanner but you haven't started one.")
               (begin (set! finished span)
                 (ly:engraver-announce-end-grob trans finished event-start)
                 (set! span '())
                 (set! event-stop '()))))
       (if (ly:stream-event? event-start)
           (begin (set! span (ly:engraver-make-grob trans 'MeasureCounter event-start))
             (set! event-start '()))))
      ((stop-translation-timestep trans)
       (if (and (ly:spanner? span)
                (null? (ly:spanner-bound span LEFT))
                (moment<=? (ly:context-property context 'measurePosition) ZERO-MOMENT)) 
           ; NOTE: the following does not work--BUG? It will cause regtest
           ; scheme-text-spanner.ly to crash!
           ;(set! (ly:spanner-bound span LEFT)
           ;   (ly:context-property context 'currentcommandColumn))
           (ly:spanner-set-bound! span LEFT 
             (ly:context-property context 'currentCommandColumn)))
       (if (and (ly:spanner? finished)
                (moment<=? (ly:context-property context 'measurePosition) ZERO-MOMENT))
           (begin
            (if (null? (ly:spanner-bound finished RIGHT))
                (ly:spanner-set-bound! finished RIGHT
                  (ly:context-property context 'currentCommandColumn)))
            (set! finished '())
            (set! event-start '())
            (set! event-stop '()))))
      ((finalize trans)
       (if (ly:spanner? finished)
           (begin
            (if (null? (ly:spanner-bound finished RIGHT))
                (set! (ly:spanner-bound finished RIGHT)
                      (ly:context-property context 'currentCommandColumn)))
            (set! finished '())))
       (if (ly:spanner? span)
           (begin
            (ly:warning "I think there's a dangling measure-attached spanner :-(")
            (ly:grob-suicide! span)
            (set! span '())))))))

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

#(allow-volta-hook "|")

\layout {
  \context {
    \Staff
    \consists #Measure_attached_spanner_engraver
    \override MeasureCounter.font-encoding = #'latin1
    \override MeasureCounter.font-size = 0
  }
}

\relative c'' {
	\key c \major \time 4/4

% Set details for later Text Spanner
\override TextSpanner #'(bound-details left text)
    = \markup { \small \bold Slower }
% Place dynamics above staff

% Place following Ottava Bracket below Text Spanners
	\repeat volta 2 {
          \set Score.measureLength = #(ly:make-moment 5 8)
          %\once \override Staff.TextSpanner.outside-staff-priority = #650
         \override Staff.MeasureCounter.stencil =
            #(lambda (grob) (test-stencil grob 
                              #{ 
                                \markup \italic 
                                %\raise #1
                                "Second time only." 
                              #} ))
          \startMeasureCount
          a16. g32 a16. f32 e8
          \set Score.repeatCommands = #'((volta "S."))
          c32 [ a16.]
          \once \hide Score.BarLine
          \once \hide Score.SpanBar
          \set Score.repeatCommands = #'((volta #f)(volta "D.") end-repeat)
          c32 [e16.]
          \set Score.measureLength = #(ly:make-moment 4/8)
          a,8 a'16. e32 f16. e32 c32 a16. 
          \stopMeasureCount
          \set Score.repeatCommands = #'((volta #f))          
          b16.[ c32 d16. e32] f32 [ a16. e16. b32]
          c8 [a] a
        } %end repeat
} %end relative