These new methods ClientConfig and Client provide the bridge into the
main plugin infrastructure by configuring and instantiating (respectively)
a client object for the referenced plugin.
This stops short of getting the proxy object from the client since that
then requires referencing the interface for the plugin kind, which would
then create a dependency on the main terraform package which we'd rather
avoid here. It'll be the responsibility of the caller in the command
package to do the final wiring to get a provider instance out of a
provider plugin client.
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.
With forthcoming support for versioned plugins we need to be able to
answer questions like what versions of plugins are currently installed,
what's the newest version of a given plugin available, etc.
PluginMetaSet gives us a building block for this sort of plugin version
wrangling.
Martin Atkins