(ly:grob-suicide! count-spanner)
(set! count-spanner '())
(ly:warning "measure count left unfinished")))))))
+
+(ly:register-translator
+ Measure_counter_engraver 'Measure_counter_engraver
+ '((grobs-created . (MeasureCounter))
+ (events-accepted . (measure-counter-event))
+ (properties-read . (currentCommandColumn
+ measurePosition
+ currentBarNumber))
+ (properties-written . ())
+ (description . "\
+This engraver numbers ranges of measures, which is useful in parts as an
+aid for counting repeated measures. There is no requirement that the
+affected measures be repeated, however. The user delimits the area to
+receive a count with @code{\\startMeasureCount} and
+@code{\\stopMeasureCount}.")))
+
+(ly:register-translator
+ Span_stem_engraver 'Span_stem_engraver
+ '((grobs-created . (Stem))
+ (events-accepted . ())
+ (properties-read . ())
+ (properties-written . ())
+ (description . "Connect cross-staff stems to the stems above in the system")))
+
+(define-public (Merge_rests_engraver context)
+"Engraver to merge rests in multiple voices on the same staff.
+
+This works by gathering all rests at a time step. If they are all of the same
+length and there are at least two they are moved to the correct location as
+if there were one voice."
+
+ (define (is-single-bar-rest? mmrest)
+ (eqv? (ly:grob-property mmrest 'measure-count) 1))
+
+ (define (is-whole-rest? rest)
+ (eqv? (ly:grob-property rest 'duration-log) 0))
+
+ (define (mmrest-offset mmrest)
+ "For single measures they should hang from the second line from the top
+ (offset of 1). For longer multimeasure rests they should be centered on the
+ middle line (offset of 0).
+ NOTE: For one-line staves full single measure rests should be positioned at
+ 0, but I don't anticipate this engraver's use in that case. No errors are
+ given in this case."
+ (if (is-single-bar-rest? mmrest) 1 0))
+
+ (define (rest-offset rest)
+ (if (is-whole-rest? rest) 1 0))
+
+ (define (rest-eqv rest-len-prop)
+ "Compare rests according the given property"
+ (define (rest-len rest) (ly:grob-property rest rest-len-prop))
+ (lambda (rest-a rest-b)
+ (eqv? (rest-len rest-a) (rest-len rest-b))))
+
+ (define (rests-all-unpitched rests)
+ "Returns true when all rests do not override the staff-position grob
+ property. When a rest has a position set we do not want to merge rests at
+ that position."
+ (every (lambda (rest) (null? (ly:grob-property rest 'staff-position))) rests))
+
+ (define (merge-mmrests rests)
+ "Move all multimeasure rests to the single voice location."
+ (if (all-equal rests (rest-eqv 'measure-count))
+ (merge-rests rests mmrest-offset)))
+
+ (define (merge-rests rests offset-function)
+ (let ((y-offset (offset-function (car rests))))
+ (for-each
+ (lambda (rest) (ly:grob-set-property! rest 'Y-offset y-offset))
+ rests))
+ (for-each
+ (lambda (rest) (ly:grob-set-property! rest 'transparent #t))
+ (cdr rests)))
+
+ (define has-one-or-less (lambda (lst) (or (null? lst) (null? (cdr lst)))))
+ (define has-at-least-two (lambda (lst) (not (has-one-or-less lst))))
+ (define (all-equal lst pred)
+ (or (has-one-or-less lst)
+ (and (pred (car lst) (cadr lst)) (all-equal (cdr lst) pred))))
+
+ (let ((curr-mmrests '())
+ (mmrests '())
+ (rests '()))
+ (make-engraver
+ ((start-translation-timestep translator)
+ (set! rests '())
+ (set! curr-mmrests '()))
+ (acknowledgers
+ ((rest-interface engraver grob source-engraver)
+ (cond
+ ((ly:context-property context 'suspendRestMerging #f)
+ #f)
+ ((grob::has-interface grob 'multi-measure-rest-interface)
+ (set! curr-mmrests (cons grob curr-mmrests)))
+ (else
+ (set! rests (cons grob rests))))))
+ ((stop-translation-timestep translator)
+ (if (and
+ (has-at-least-two rests)
+ (all-equal rests (rest-eqv 'duration-log))
+ (rests-all-unpitched rests))
+ (merge-rests rests rest-offset))
+ (if (has-at-least-two curr-mmrests)
+ (set! mmrests (cons curr-mmrests mmrests))))
+ ((finalize translator)
+ (for-each merge-mmrests mmrests)))))