introduce AbsMoveableResource

AbsMoveableResource is an AbsMoveable that is either a resource or a resource
instance. This interface represents a moveable that has a resource type.

internal/addrs/moveable.go

@@ -24,6 +24,19 @@ var (
 	_ AbsMoveable = AbsModuleCall{}
 )
 
+// AbsMoveableResource is an AbsMoveable that is either a resource or a resource
+// instance.
+type AbsMoveableResource interface {
+	AbsMoveable
+	Type() string
+}
+
+// The following are all of the possible AbsMoveableResource types:
+var (
+	_ AbsMoveableResource = AbsResource{}
+	_ AbsMoveableResource = AbsResourceInstance{}
+)
+
 // ConfigMoveable is similar to AbsMoveable but represents a static object in
 // the configuration, rather than an instance of that object created by
 // module expansion.

internal/addrs/resource.go

@@ -186,6 +186,10 @@ func (r AbsResource) String() string {
 	return fmt.Sprintf("%s.%s", r.Module.String(), r.Resource.String())
 }
 
+func (r AbsResource) Type() string {
+	return r.Resource.Type
+}
+
 func (r AbsResource) Equal(o AbsResource) bool {
 	return r.Module.Equal(o.Module) && r.Resource.Equal(o.Resource)
 }
@@ -267,6 +271,10 @@ func (r AbsResourceInstance) String() string {
 	return fmt.Sprintf("%s.%s", r.Module.String(), r.Resource.String())
 }
 
+func (r AbsResourceInstance) Type() string {
+	return r.Resource.Resource.Type
+}
+
 func (r AbsResourceInstance) Equal(o AbsResourceInstance) bool {
 	return r.Module.Equal(o.Module) && r.Resource.Equal(o.Resource)
 }

internal/refactoring/move_validate.go

@@ -251,29 +251,17 @@ func moveableObjectExists(addr addrs.AbsMoveable, in instances.Set) bool {
 func resourceTypesDiffer(absFrom, absTo addrs.AbsMoveable) bool {
 	switch absFrom.(type) {
 	case addrs.AbsResourceInstance, addrs.AbsResource:
+		absFrom := absFrom.(addrs.AbsMoveableResource)
 		// addrs.UnifyMoveEndpoints guarantees that both addresses are of the
-		// same kind, so at this point we can assume that absTo is an
+		// same kind, so at this point we can assume that absTo is also an
 		// addrs.AbsResourceInstance or addrs.AbsResource.
-		return absMoveableResourceType(absFrom) != absMoveableResourceType(absTo)
+		absTo := absTo.(addrs.AbsMoveableResource)
+		return absFrom.Type() != absTo.Type()
 	default:
 		return false
 	}
 }
 
-// absMoveableResourceType returns the type of the supplied
-// addrs.AbsResourceInstance or addrs.AbsResource, or "" for other AbsMoveable
-// types.
-func absMoveableResourceType(addr addrs.AbsMoveable) string {
-	switch addr := addr.(type) {
-	case addrs.AbsResourceInstance:
-		return addr.Resource.Resource.Type
-	case addrs.AbsResource:
-		return addr.Resource.Type
-	default:
-		return ""
-	}
-}
-
 func movableObjectDeclRange(addr addrs.AbsMoveable, cfg *configs.Config) (tfdiags.SourceRange, bool) {
 	switch addr := addr.(type) {
 	case addrs.ModuleInstance: