Since the command package also needs to know about the specific OS_ARCH
directories, remove the logic fom the discovery package.
This doesn't completely remove the knowledge of the path from discovery,
in order to maintain the current behavior of skipping legacy plugin
names within a new-style path.
This is used to mark the plugin protocol version. Currently we actually
just ignore this entirely, since only one protocol version exists anyway.
Later we will need to add checks here to ensure that we only pay attention
to plugins of the right version.
The semver library we were using doesn't have support for a "pessimistic
constraint" where e.g. the user wants to accept only minor or patch
version upgrades. This is important for providers since users will
generally want to pin their dependencies to not inadvertantly accept
breaking changes.
So here we switch to hashicorp's home-grown go-version library, which
has the ~> constraint operator for this sort of constraint.
Given how much the old version object was already intruding into the
interface and creating dependency noise in callers, this also now wraps
the "raw" go-version objects in package-local structs, thus keeping the
details encapsulated and allowing callers to deal just with this package's
own types.
For now this supports both our old and new directory layouts, so we can
preserve compatibility with existing configurations until a future major
release where support for the old paths will be removed.
Currently this allows both styles in all given directories, which means we
support more variants than we actually intend to but this is accepted to
keep the interface simple such that we can easily remove the legacy
exception later. The documentation will reflect only the subset of
path layouts that we actually intend to support.
James Bardin