Overuse of variant() in package.py recipes

[teonnik]

Packages such as intel-mkl, intel-parallel-studio and others define variant() that do not change the final binaries produced by the recipe. These variants only serve to propagate information about a component of the package to dependent packages. The unfortunate consequence is that changing the variant, often triggers unnecessary installations that are essentially duplicates.

In the case of intel-parallel-studio some of the variants serve as aliases to the version information encoded in the package. That provides, perhaps, a convenient way to express a spec but introduces yet another avenue for triggering unnecessary installs.

A PR attempting to address these issues for intel-mkl and intel-parallel-studio was opened here: #15567 .

Perhaps the overuse of variant() can be addressed by provides()? Unfortunately, it isn't clear from the documentation what qualifies as a virtual package.

Since changing a variant() always triggers an install, it would be better if it is only used for options that change the binary output of a recipe.

Additional information

• I have searched the issues of this repo and believe this is not a duplicate