backend/remote-state/gcs: Implement the "region" config option.

This allows to select the region in which a bucket is created.
This copies behavior from the Google Cloud provider.

backend/remote-state/gcs/backend.go

@@ -28,6 +28,7 @@ type gcsBackend struct {
 	defaultStateFile string
 
 	projectID string
+	region    string
 }
 
 func New() backend.Backend {
@@ -67,6 +68,13 @@ func New() backend.Backend {
 				Description: "Google Cloud Project ID",
 				Default:     "",
 			},
+
+			"region": {
+				Type:        schema.TypeString,
+				Optional:    true,
+				Description: "Region / location in which to create the bucket",
+				Default:     "",
+			},
 		},
 	}
 
@@ -95,6 +103,10 @@ func (b *gcsBackend) configure(ctx context.Context) error {
 	if id := os.Getenv("GOOGLE_PROJECT"); b.projectID == "" && id != "" {
 		b.projectID = id
 	}
+	b.region = data.Get("region").(string)
+	if r := os.Getenv("GOOGLE_REGION"); b.projectID == "" && r != "" {
+		b.region = r
+	}
 
 	opts := []option.ClientOption{
 		option.WithScopes(storage.ScopeReadWrite),
@@ -128,6 +140,7 @@ func (b *gcsBackend) ensureBucketExists() error {
 
 	attrs := &storage.BucketAttrs{
 		VersioningEnabled: true,
+		Location:          b.region,
 	}
 
 	return b.storageClient.Bucket(b.bucketName).Create(b.storageContext, b.projectID, attrs)

website/docs/backends/types/gcs.html.md

@@ -57,3 +57,5 @@ The following configuration options are supported:
  *  `path` - (Deprecated) GCS path to the state file of the default state. For backwards compatibility only, use `prefix` instead.
  *  `project` / `GOOGLE_PROJECT` - (Optional) The project ID to which the bucket belongs. This is only used when creating a new bucket during initialization.
     Since buckets have globally unique names, the project ID is not required to access the bucket during normal operation.
+ *  `region` / `GOOGLE_REGION` - (Optional) The region in which a new bucket is created.
+    For more information, see [Bucket Locations](https://cloud.google.com/storage/docs/bucket-locations).