This exercises the ability to customize the installation methods used by
the provider plugin installer, in this case forcing the use of a custom
local directory with a result essentially the same as what happens when
you pass -plugin-dir to "terraform init".
This more closely replicates the 0.12-and-earlier behavior, where having
at least one version of a provider installed locally would totally disable
any attempt to look for newer versions remotely.
This is just for the implicit default behavior. Assumption is that later
we'll have an explicit configuration mechanism that will allow the user
to specify exactly where to look for what, and thus avoid tricky
heuristics like this.
In the new design the ProviderSource is decided by package main, not by
the "command" package, and so making sure the vendor directory is included
is the responsibility of that package instead. Therefore we can no longer
test this at the "command" package level, but we'll retain a test for it
in e2etests to record that it isn't currently working, so that we have
a prompt to fix it before releasing.
Due to some incomplete rework of this function in an earlier commit, the
safety check for using the same directory as both the target and the
cache was inverted and was raising an error _unless_ they matched, rather
than _if_ they matched.
This change is verified by the e2etest TestInitProviders_pluginCache,
which is also updated to use the new-style cache directory layout as part
of this commit.
Martin Atkins