ly:set-option png backend broken?

[Stefano Antonelli]

Hello list,

If I add this line to my ly file:

#(ly:set-option 'backend 'png)

on 2.20.0 (linux), I get this warning:

warning: program option -dprint-pages not supported by backend `png'

on 2.24.3 (wine and linux), same file, I get this failure:

C:/lilypond-2.24.3/share/lilypond/2.24.3/ly/init.ly:65:2: error: Guile
signaled an error for the expression beginning here
#
 (let ((book-handler (if (defined? 'default-toplevel-book-handler)
In procedure module-lookup: Unbound variable: output-stencils

The file looks like this:

theMusic = \new Staff {
        c4 d e f
        g4 a b c
        d4 e f g
}

\score {
        \unfoldRepeats { \theMusic }

        \layout { }
        \midi { }
}

#(ly:set-option 'backend 'png)

I was going to ask why setting the png backend this way differs from
adding --png to the command line.  I thought I'd test it in 2.24.3
first in case it was fixed.

Is there a bug in 2.24.3?  Or is there something quasi wrong with the
syntax?

In the 2.20.0 version, no png is produced.  I can make the warning go
away with:

#(ly:set-option 'print-pages #f)
#(ly:set-option 'backend 'png)

but still no png is produced.  If I take those lines out and run:

lilypond --png test.ly

then a png is produced.  It's odd behaviour.

Thanks,
Stef