terraform-provider-google/google/resource_google_project_migrate.go

package google

import (
	"fmt"
	"log"

	"github.com/hashicorp/terraform/terraform"
)

func resourceGoogleProjectMigrateState(v int, s *terraform.InstanceState, meta interface{}) (*terraform.InstanceState, error) {
	if s.Empty() {
		log.Println("[DEBUG] Empty InstanceState; nothing to migrate.")
		return s, nil
	}

	switch v {
	case 0:
		log.Println("[INFO] Found Google Project State v0; migrating to v1")
		s, err := migrateGoogleProjectStateV0toV1(s, meta.(*Config))
		if err != nil {
			return s, err
		}
		return s, nil
	default:
		return s, fmt.Errorf("Unexpected schema version: %d", v)
	}
}

// This migration adjusts google_project resources to include several additional attributes
// required to support project creation/deletion that was added in V1.
func migrateGoogleProjectStateV0toV1(s *terraform.InstanceState, config *Config) (*terraform.InstanceState, error) {
	log.Printf("[DEBUG] Attributes before migration: %#v", s.Attributes)

	s.Attributes["skip_delete"] = "true"
	s.Attributes["project_id"] = s.ID

	if s.Attributes["policy_data"] != "" {
		p, err := getProjectIamPolicy(s.ID, config)
		if err != nil {
			return s, fmt.Errorf("Could not retrieve project's IAM policy while attempting to migrate state from V0 to V1: %v", err)
		}
		s.Attributes["policy_etag"] = p.Etag
	}

	log.Printf("[DEBUG] Attributes after migration: %#v", s.Attributes)
	return s, nil
}