+(define pure-print-callbacks
+ (list
+ ly:note-head::print
+ ly:clef::print
+ ly:text-interface::print
+ ly:script-interface::print))
+
+;; ly:grob::stencil-extent is safe iff the print callback is safe too
+(define (pure-stencil-height grob start stop)
+ (let ((sten (ly:grob-property-data grob 'stencil)))
+ (if (or
+ (ly:stencil? sten)
+ (memq sten pure-print-callbacks))
+ (ly:grob::stencil-height grob)
+ '(0 . 0))))
+
+(define pure-conversions-alist
+ (list
+ `(,ly:slur::outside-slur-callback . ,ly:slur::pure-outside-slur-callback)
+ `(,ly:stem::height . ,ly:stem::pure-height)
+ `(,ly:grob::stencil-height . ,pure-stencil-height)
+ `(,ly:side-position-interface::y-aligned-side . ,ly:side-position-interface::pure-y-aligned-side)
+ `(,ly:axis-group-interface::height . ,ly:axis-group-interface::pure-height)
+ `(,ly:hara-kiri-group-spanner::y-extent . ,ly:hara-kiri-group-spanner::pure-height)
+ `(,ly:slur::height . ,ly:slur::pure-height)
+ `(,ly:side-position-interface::y-aligned-side . ,ly:side-position-interface::pure-y-aligned-side)))
+
+(define pure-functions
+ (list
+ ly:staff-symbol-referencer::callback
+ ly:staff-symbol::height))
+
+(define-public (pure-relevant grob)
+ (let ((extent-callback (ly:grob-property-data grob 'Y-extent)))
+ (not (eq? #f
+ (or
+ (pair? extent-callback)
+ (memq extent-callback pure-functions)
+ (and
+ (pair? (assq extent-callback pure-conversions-alist))
+ (begin
+ (or
+ (not (eq? extent-callback ly:grob::stencil-height))
+ (memq (ly:grob-property-data grob 'stencil) pure-print-callbacks)
+ (ly:stencil? (ly:grob-property-data grob 'stencil))))))))))
+
+(define-public (call-pure-function unpure args start end)
+ (if (ly:simple-closure? unpure)
+ (ly:eval-simple-closure (car args) unpure start end)
+ (if (not (procedure? unpure))
+ unpure
+ (if (memq unpure pure-functions)
+ (apply unpure args)
+ (let ((pure (assq unpure pure-conversions-alist)))
+ (if pure
+ (apply (cdr pure) (append (list (car args) start end) (cdr args)))))))))