helper/schema: start the resource importer

helper/schema/resource_importer.go

@@ -0,0 +1,30 @@
+package schema
+
+// ResourceImporter defines how a resource is imported in Terraform. This
+// can be set onto a Resource struct to make it Importable. Not all resources
+// have to be importable; if a Resource doesn't have a ResourceImporter then
+// it won't be importable.
+//
+// "Importing" in Terraform is the process of taking an already-created
+// resource and bringing it under Terraform management. This can include
+// updating Terraform state, generating Terraform configuration, etc.
+type ResourceImporter struct {
+	// The functions below must all be implemented for importing to work.
+
+	// State is called to convert an ID to one or more InstanceState to
+	// insert into the Terraform state.
+	State StateFunc
+}
+
+// StateFunc is the function called to import a resource into the
+// Terraform state. It is given a ResourceData with only ID set. This
+// ID is going to be an arbitrary value given by the user and may not map
+// directly to the ID format that the resource expects, so that should
+// be validated.
+//
+// This should return a slice of ResourceData that turn into the state
+// that was imported. This might be as simple as returning only the argument
+// that was given to the function. In other cases (such as AWS security groups),
+// an import may fan out to multiple resources and this will have to return
+// multiple.
+type StateFunc func(*ResourceData, interface{}) ([]*ResourceData, error)