We can get a conflict when trying to install a package that has dependencies that themselves depend on different variants of a dependent package. For instance:

[lee218@hype2:spack]$ spack -v install py-basemap
==> Error: Invalid spec: '[email protected]%[email protected]~python=chaos_6_x86_64_ib^[email protected]%[email protected]=chaos_6_x86_64_ib^[email protected]%[email protected]=chaos_6_x86_64_ib'. Package libxml2 requires variant +python, but spec asked for ~python

The underlying problem is that the mesa package requests libxml2+python, while qt and fontconfig just request libxml2. I can work around this by explicitly requesting "py-basemap^libxml2+python".