\version "2.19.17"

#(define (remove-first symbol alist)
   "Remove the first key-value pair of association list @var{alist}
whose key matches @var{symbol}."
   (let loop ((alist alist) (result '()))
     (cond
      ((null? alist) result)
      ((eq? (caar alist) symbol)
       (append result (cdr alist)))
      (else (loop (cdr alist)
              (append result (list (car alist))))))))

#(define (grob::has-default-prop grob prop)
   "Check all-grob-descriptions to see if symbol @var{grob} has
a default setting for symbol @var{prop}.  Either return the
setting or @code{#f}."
   (let ((description (assoc-get grob all-grob-descriptions)))
     (if description
         (assoc-get 'stencil description))))

#(define (mark-tweak grob)
   (let* ((default (assoc-get (grob::name grob) all-grob-descriptions)) 
          (props (ly:grob-basic-properties grob))
          ;; Our procedure has been added to the head of grob's basic
          ;; properties.  Let's not count it as a tweak!
          (props
           (remove
            (lambda (p)
              (and (procedure? (cdr p))
                   (eq? (procedure-name (cdr p)) 'mark-tweak)))
            props))
          ;; We're using after-line-breaking to set color of stencil, but
          ;; let's preserve its last setting
          (after-line-return (assoc-get 'after-line-breaking props))
          ;; Clef.glyph doesn't appear in all-grob-descriptions, but it
          ;; is set at some point automatically.  Don't mark it unless
          ;; it genuinely is a user override.  There may be other
          ;; such grobs.
          (props
           (if (eq? (grob::name grob) 'Clef)
               (reverse (remove-first 'glyph (reverse props)))
               props))
          (diff (lset-difference eq? props default)))
     ;; Tweaks will not appear in the "basic properties" alist of our grob, but
     ;; we can find them through the music event which led to the grob.  This
     ;; is available through the stream-event which caused our grob.
     (if (null? diff)
         (let* ((cause (event-cause grob))
                (tweaks (and cause
                             (ly:music-property
                              (ly:event-property cause 'music-cause)
                              'tweaks))))
           (if (pair? tweaks)
               (set! (ly:grob-property grob 'color) red)))
         (set! (ly:grob-property grob 'color) green))
     
     ;; Return any default setting of after-line-breaking.
     after-line-return))

colorTweaksEngraver =
#(lambda (context)
   (make-engraver 
    (acknowledgers
     ((grob-interface engraver grob source-engraver)
      (if (grob::has-default-prop grob 'stencil)
          (set! (ly:grob-property grob 'after-line-breaking)
                (mark-tweak grob)))))))



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

{ 
  \voiceOne
  \once \override Staff.Clef.extra-offset = #'(0 . 2)
  c^"hi"_1 \clef "bass_8" c,
  \oneVoice
  \key d \major
  c,
}

{
  \override NoteHead.X-extent = #'(-1 . 1)
  \override NoteHead.font-size = 3
  \override NoteHead.stencil = #ly:note-head::print
  c1
  \revert NoteHead.X-extent
  c1
  \revert NoteHead.font-size
  c1
  \revert NoteHead.stencil
  c1
}


{
  %\voiceTwo
  \tweak font-size 3
  c'1
  \tweak NoteHead.font-size 3
  \tweak Stem.thickness 5
  c'2
  <c' \tweak font-size 3 e'>
  <\tweak NoteHead.font-size 3 c' e'>1
  \override NoteHead.font-size = 4
  c'1
  \temporary \override NoteHead.font-size = 12
  c'1
  \revert NoteHead.font-size
  \revert Score.BarLine.X-extent
  \revert Staff.Clef.after-line-breaking
  \clef alto
  c'1
}

\layout {
  \context {
    \Score {
      \override BarLine.X-extent = #'(-2 . 2)
    }
  }
  \context {
    \Staff
    \override Clef.after-line-breaking =
    #(lambda (grob)
       (set! (ly:grob-property grob 'stencil)
             (ly:stencil-rotate (ly:clef::print grob) -15 0 0)))
 
  }
}


\layout {
  \context {
    \Score
    \consists \colorTweaksEngraver
  }
}