Unfortunately in the user model the noun "source" is already used for the
argument in the required_providers block to specify which provider to use,
so it's confusing to use the same noun to also refer to the method used to
obtain that provider.
In the hope of mitigating that confusion, here we use the noun "method",
as in "installation method", to talk about the decision between getting
a provider directly from its origin registry or getting it from some
mirror. This is distinct from the provider's "source", which is the
location where a provider _originates_ (prior to mirroring).
This noun is also not super awesome, but better than overloading an
existing term in the same feature.
This new CLI config block type allows explicitly specifying where
Terraform should look to find provider plugins for installation. This is
not used anywhere as of this commit, but in a future commit we'll change
package main to treat the presence of a block of this type as a request
to disable the default set of provider sources and use these explicitly-
specified ones instead.
This is just a wholesale move of the CLI configuration types and functions
from the main package into its own package, leaving behind some type
aliases and wrappers for now to keep existing callers working.
This commit alone doesn't really achieve anything, but in future commits
we'll expand the functionality in this package.
Martin Atkins