Re: Duplicate SVG attribute

[Jean Abou Samra]

Le 24/12/2022 à 15:38, Paolo Prete a écrit :

Hello,

I'm noting that the generated SVG of this...:

{
     \once \override DynamicText.output-attributes.val = "x"
     \once \override DynamicText.output-attributes.val = "y"
     c'\mf
}

... creates the following SVG tag, with a duplicate "val" attribute:
<g val="y" val="x">

I've opened https://gitlab.com/lilypond/lilypond/-/issues/6494





\version "2.25.0"

\new Voice <<
  { \once \override NoteHead.color = red c' }
  { \once \override NoteHead.color = blue d' }
>>

It is unusual, though, to do two \once \override for the same grob property at the same time. I would say it's reasonable to expect this to work when the overrides are together in sequential music ({ ... }) like this, but it is preferable not to do it in parallel music like because in more complex cases, it gets tricky for LilyPond to determine which override is meant to have precedence.

Is this a bug? Also note that the duplication doesn't happen if I use
"\override" instead of "\once \override".

In case of a bug, is there a workaround for it (I mean: is there a way to
call \once \override multiple times for the same attribute without
duplicating it)?

\version "2.25.0"

#(define* (my-uniq-list lst #:optional (cmp equal?))
  (reverse!
   (fold (lambda (x acc)
           (if (null? acc)
               (list x)
               (if (cmp x (car acc))
                   acc
                   (cons x acc))))
         '() lst) '()))


#(set! (@@ (lily output-svg) stencil-dispatch-alist)
       (assq-set!
        (@@ (lily output-svg) stencil-dispatch-alist)
        'start-group-node
        (lambda (attrs)
          (format
           #f
           "<g ~a>\n"
           (string-concatenate
            (map (match-lambda
                   ((attr . val) (ly:format " ~a=\"~a\"" attr val)))
                 (my-uniq-list
                  (sort attrs

                  (comparator-from-key car eq?))))))))

{
    \once \override DynamicText.output-attributes.val = "x"
    \once \override DynamicText.output-attributes.val = "y"
    c'\mf
}

                        (comparator-from-key car (comparator-from-key symbol->string string<?))) With the usual warning when using @@ that you should not expect any sort of stability for this kind of code.

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