Getting GEM_PATH right for ruby scripts

[Stephen Paul Weber]

Hello everyone!

I've finally been diving deep into the Guix and doing a lot of packaging.  One
thing that has now come to my attention is the way ruby-build-system set
GEM_PATH for wrapped scripts.  It takes the whole GEM_PATH that is present at
build time.  This means that all those packages end up keeping store references
to build-only (indeed, unit-test-only!) dependencies such as rake and minitest.

Of course the problem is that the package specification does not have any way to
know which inputs are going to be needed past build time.  In the ruby packages,
convention is to use propogated-inputs for this, but even so the GEM_PATH we
need would be for all the implicitly propogated inputs.  I guess there should be
some way to get this, since it's what GEM_PATH will be in a profile that the
package is installed to?

I'm sure topics like this have been beaten to death, but I'd like to understand
how things are and if they can be improved as much as will fit in my head.

Thanks,

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