Not sure if this is a duplicate issue but it would be nice to have the ability to specify variants for external packages and have them used. An example:

We want to link with cray-petsc and there are currently 4 different cray-petsc's to link to:
{cray-petsc, cray-petsc-64, cray-petsc-complex, cray-petsc-complex-64}

I was hoping to be able to add this to packages.yaml

packages:
   petsc:
       buildable: false
       modules:
             petsc@X.X.X: cray-petsc
             petsc@X.X.X+int64: cray-petsc-64
             petsc@X.X.X+complex: cray-petsc-complex
             petsc@X.X.X+int64+complex: cray-petsc-complex-64

Unfortunately whenever I do spack spec petsc+int64 or any of the ones with variants, I always get the defaults set by package.py.

This is a problem since some of the cray packages we need to link with have variants with them.