%by: ArnoldTheresius

#(define-public (Local_repeatcommands_graceecho_purger ctx)
  (let ((last-main-moment -1)
        (accumulated-repeat-list '()))
    (make-engraver
      ((process-music trans)
         (let*
           ((now-mom (ly:context-current-moment ctx))
            (now-main-mom (ly:moment-main now-mom))
            (current-repeat-list (ly:context-property ctx 'repeatCommands)))
           (if (not (equal? last-main-moment now-main-mom))
               (set! accumulated-repeat-list '()))
           (if (not (null? current-repeat-list))
               (let ((new-repeat-list '()))
                (for-each 
                  (lambda (x)
                    (let ((tokken x))
                      (if (pair? x) ;;; only volta expected!
                          (if (and (boolean? (cadr x)) (eq? (cadr x) #f))
                            (set! tokken 'volta--end)
                            (set! tokken 'volta--start)))
                      (if (not (memq tokken accumulated-repeat-list)) 
                          (begin
                            (set! new-repeat-list (cons x new-repeat-list))
                            (set! accumulated-repeat-list 
                                  (cons tokken accumulated-repeat-list)))))) 
                  current-repeat-list)
                (ly:context-set-property! 
                  ctx 'repeatCommands 
                  (reverse! new-repeat-list))))
           (set! last-main-moment now-main-mom))))))



Music = {
  \tag #'Grace \acciaccatura b8 c'1
  \inStaffSegno
  \repeat volta 2 {
    \tag #'Grace \acciaccatura b8 c'1
  }
  \alternative {
    {
      \tag #'Grace \acciaccatura b8 c'1
    } {
      \tag #'Grace \acciaccatura b8 c'1
    }
  }
  \tag #'Grace \acciaccatura b8 c'1
}

\score {
  \new StaffGroup <<
    \new Staff {
      \Music
    }
    \new Staff {
      \removeWithTag #'Grace \Music
    }
  >>
  \layout {
    \context { \Score
      \remove "Repeat_acknowledge_engraver"
      \remove "Volta_engraver"
      % this scheme engraver defined above must be placed
      % before the 'Repeat_acknowledge_engraver', and all
      % dependent engravers (i.e. the "Volta_engraver")
      % must follow.
      % As there is no »before engraver xxx« option in
      % the '\consists' command, I did remove both before
      % I added the new scheme engraver, then I added
      % the two engravers again.
      \consists #Local_repeatcommands_graceecho_purger
      \consists "Repeat_acknowledge_engraver"
      \consists "Volta_engraver"

      %%% I have already patched my LILYPOND as listed below!
      %%% This is the syntax how to disable this patch in a \score block
      % \remove #Repeatcommands_graceecho_purger
    }
  }
}

\score {
  \new Staff { e'1 \inStaffSegno e' \inStaffSegno \repeat volta 2 { e' }  }
}

\markup \wordwrap {
  If you want to use it in every compilation, you may patch your LILYPOND installation:
  Follow the instruction you'll find here in the source code.
}
%{
  PATCH INSTRUCTION:

  1. locate the file
     .../usr/share/lilypond/current/scm/music-functions.scm
     and append these 27 lines:
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Extension for grace echo purging
(define-public (Repeatcommands_graceecho_purger ctx)
  (let ((last-main-moment -1)
        (accumulated-repeat-list '()))
    (make-engraver
      ((process-music trans)
       (let*
         ((now-mom (ly:context-current-moment ctx))
          (now-main-mom (ly:moment-main now-mom))
          (current-repeat-list (ly:context-property ctx 'repeatCommands)))
         (if (not (equal? last-main-moment now-main-mom))
           (set! accumulated-repeat-list '()))
         (if (not (null? current-repeat-list))
           (let ((new-repeat-list '()))
            (for-each (lambda (x)
              (let ((tokken x))
                (if (pair? x) ;;; only volta expected!
                  (if (and (boolean? (cadr x)) (eq? (cadr x) #f))
                    (set! tokken 'volta--end)
                    (set! tokken 'volta--start)))
                (if (not (memq tokken accumulated-repeat-list)) (begin
                  (set! new-repeat-list (cons x new-repeat-list))
                  (set! accumulated-repeat-list (cons tokken accumulated-repeat-list)))))
             ) current-repeat-list)
            (ly:context-set-property! ctx 'repeatCommands (reverse! new-repeat-list))))
         (set! last-main-moment now-main-mom))))))

  2. locate the file
     .../usr/share/lilypond/current/ly/engraver-init.ly,
     open it with an text editor,
     find the line containing
       \consists "Repeat_acknowledge_engraver"
     and add just _b_e_f_o_r_e_ this the line
       \consists #Repeatcommands_graceecho_purger

%}