Long story short: $ emerge -1v lightspark --onlydeps --exclude llvm --jobs These are the packages that would be merged, in order: Calculating dependencies... done! !!! All ebuilds that could satisfy "<sys-devel/llvm-3.7" have been masked. [...] What I would love to see instead, emerge ignoring '<sys-devel/llvm-3.7' dep since I explicitly exclude it, and we are not installing the package in question anyway. Alternatively, we could go for some kind of pretend-exclude that would assume the dep is satisfied while preventing the dep package from being altered.
I think this is fine as long as we ensure that all of the dependencies are satisfied for those packages that are really being installed. For example, one of those packages might have a dependency on a package that you've tried to exclude, and it should be an error if that results in an unsatisfied dependency.