core: fix inheritence checks in ConfigTreeDependencies

Due to some disagreement about what representation of provider addresses
we were using, the inherited providers map wasn't matching. Now we'll
consistenly use the "compact" form (just the provider name and optional
alias).

Also includes some other tweaks to make this test better-behaved.

terraform/module_dependencies.go

@@ -34,7 +34,8 @@ func configTreeConfigDependencies(root *configs.Config, inheritProviders map[str
 		// This isn't necessarily correct if we're called with a nil that
 		// *isn't* at the root, but in practice that can never happen.
 		return &moduledeps.Module{
-			Name: "root",
+			Name:      "root",
+			Providers: make(moduledeps.Providers),
 		}
 	}
 
@@ -109,7 +110,7 @@ func configTreeConfigDependencies(root *configs.Config, inheritProviders map[str
 			}
 
 			reason := moduledeps.ProviderDependencyImplicit
-			if _, inherited := inheritProviders[addr.String()]; inherited {
+			if _, inherited := inheritProviders[addr.StringCompact()]; inherited {
 				reason = moduledeps.ProviderDependencyInherited
 			}
 

terraform/module_dependencies_test.go

@@ -3,7 +3,7 @@ package terraform
 import (
 	"testing"
 
-	"github.com/davecgh/go-spew/spew"
+	"github.com/go-test/deep"
 	"github.com/hashicorp/terraform/configs"
 	"github.com/hashicorp/terraform/moduledeps"
 	"github.com/hashicorp/terraform/plugin/discovery"
@@ -249,12 +249,8 @@ func TestModuleTreeDependencies(t *testing.T) {
 			}
 
 			got := ConfigTreeDependencies(root, test.State)
-			if !got.Equal(test.Want) {
-				t.Errorf(
-					"wrong dependency tree\ngot:  %s\nwant: %s",
-					spew.Sdump(got),
-					spew.Sdump(test.Want),
-				)
+			for _, problem := range deep.Equal(got, test.Want) {
+				t.Error(problem)
 			}
 		})
 	}