internal/getproviders: Distinguished packed vs. unpacked local packages

Our local filesystem mirror mechanism will allow provider packages to be
given either in packed form as an archive directly downloaded to disk or
in an unpacked form where the archive is extracted.

Distinguishing these two cases in the concrete Location types will allow
callers to reliably select the mode chosen by the selected installation
source and handle it appropriately, rather than resorting to out-of-band
heuristics like checking whether the object is a directory or a file.

internal/getproviders/types.go

@@ -59,19 +59,27 @@ type PackageMeta struct {
 }
 
 // PackageLocation represents a location where a provider distribution package
-// can be obtained. A value of this type contains either a PackageLocalPath or a
-// PackageHTTPURL value.
+// can be obtained. A value of this type contains one of the following
+// concrete types: PackageLocalArchive, PackageLocalDir, or PackageHTTPURL.
 type PackageLocation interface {
 	packageLocation()
 }
 
-// PackageLocalPath is a provider package location in the local filesystem.
-// Its value is a local filesystem path using the syntax understood by Go's
-// standard path/filepath package on the operating system where Terraform is
-// running.
-type PackageLocalPath string
+// PackageLocalArchive is the location of a provider distribution archive file
+// in the local filesystem. Its value is a local filesystem path using the
+// syntax understood by Go's standard path/filepath package on the operating
+// system where Terraform is running.
+type PackageLocalArchive string
 
-func (p PackageLocalPath) packageLocation() {}
+func (p PackageLocalArchive) packageLocation() {}
+
+// PackageLocalDir is the location of a directory containing an unpacked
+// provider distribution archive in the local filesystem. Its value is a local
+// filesystem path using the syntax understood by Go's standard path/filepath
+// package on the operating system where Terraform is running.
+type PackageLocalDir string
+
+func (p PackageLocalDir) packageLocation() {}
 
 // PackageHTTPURL is a provider package location accessible via HTTP.
 // Its value is a URL string using either the http: scheme or the https: scheme.