I'm sure there are many use cases I'm ignoring, particularly with things like PYTHONPATH and PERL5LIB where we need to recursively set env vars for language dependencies, but I think we currently overuse setup_dependent_*_environment. I can't think of a case where it should be used aside from an extendable = True package.

To elaborate further on this, I think there are really only 2 types of environment variables, ones needed to build a package and ones needed to run a package. In my mind, the only point of the setup_dependent_*_environment functions was so that we didn't have to write:

def setup_run_environment(self, env):
    env.prepend_path('PYTHONPATH', site_packages_dir)

in every single Python package. But if we subsume this into the PythonPackage base class, this is no longer an issue. So basically, I see why setup_dependent_*_environment can be convenient, but I don't think it's necessary.

@alalazo @scheibelp @becker33 @tgamblin I know I opened this issue at an inopportune time (during Thanksgiving break), but I was wondering if any of you have any opinions on this. Basically what I'm proposing is that:

1. setup_dependent_build_environment can be replaced by a call to setup_run_environment for all build dependencies
2. setup_dependent_run_environment can be replaced by a call to setup_run_environment for all run dependencies, or gotten rid of by autoloading run dependencies via modules

See #14191 and #14198 for another unfortunate victim of this confusion.

@adamjstewart Agreed, I was just refactoring a small package (not in the main spack repo) to add these methods and was struggling to discern the difference between the run environment and the dependent environments. Fortunately it's not too hard to reuse these functions:

    def setup_run_environment(self, env):
        env.set('DATAPATH', self.prefix)

    def setup_dependent_build_environment(self, env, dependent_spec):
        self.setup_run_environment(env)

    setup_dependent_run_environment = setup_dependent_build_environment

Note that this distinction between dependent_run_environment and run_environment makes it unclear to me what spack load x and spack env activate x is supposed to do... run both for all transitive run type deps?

I would expect setup_run_environment to be executed for all transitive run type deps, as well as setup_dependent_run_environment, but this was not the default behavior for a long time. In #23368 it was confirmed that this is the expected behavior.

Then what's the point of setup_dependent_run_environment except for causing confusion?