Looking at the graphicmagic files, it doesn't use modules as imagemagick does. Unless there is a configure option to build modules ( --with-modules or one with another name), it looks like optdepends won't be possible. If modules is possible, then other depends might become optdepends too.

BTW, perllocal.pod and .packlist are removed automatically by makepkg, so the last lines of the package function can be removed.

Thanks for the tip about the extra files. I'll see what the --with-modules configure option can do for us.

If I just add '--with-modules' to the current PKGBUILD, without adding/removing any dependency, I get strange errors like "gm convert: No decode delegate for this image format (bla.jpg)."
The modules build probably needs a bit of work...

Maybe a missing depends? Is it the same with other formats? You can always check the imagemagick PKGBUILD for ideas.

Eric: I do not believe it is a dependency issue: if I build without --with-modules I can do `gm convert bla.jpg bla.png` without a problem. If I build with --with-modules (without removing/adding any other package on my system) then this gives the error above. I'll have a look at imagemagick's PKGBUILD later, thanks.

When using modules, graphicsmagick uses libtool to open modules. Compiling with modules would need options=(libtool).

Ah. Of course, that makes sense. Thanks.

That libtool issue hadn't crossed my mind but it needs the modules' libtool files. You can manually remove the library libtool files if you want (that what's done for imagemagick):
rm -f "${pkgdir}"/usr/lib/*.la

Looking at imagemagick's .la files:

dependency_libs=' /usr/lib/libMagickCore-6.Q16HDRI.la -llcms2 -llqr-1 -lglib-2.0 -lfontconfig -lfreetype -lXext -lX11 -lXt -llzma -lbz2 -lz -lltdl -lgomp -lOpenCL -lm'

The module .la files have dependencies on the .la files in /usr/lib, so if you delete them, the dependencies can't resolve anymore. Don't know if this is a problem for imagemagick/graphicsmagick, but for libsasl/cyrus-sasl it was.

It's not an issue for imagemagick, the .la files in /usr/lib were removed several years ago without any problem.

I've decided to leave the libtool files under /usr/lib alone: they amount to a few kB only, and this keeps the package() function as simple as it currently is...