You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: spanner_update_instance_config.go
    path of file: ./repos/golang-samples/spanner/spanner_snippets/spanner
    
    the code of the file until where you have to start completion: // Copyright 2022 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package spanner

// [START spanner_update_instance_config]

import (
	"context"
	"fmt"
	"io"
	"time"

	instance "cloud.google.com/go/spanner/admin/instance/apiv1"
	instancepb "google.golang.org/genproto/googleapis/spanner/admin/instance/v1"
	"google.golang.org/genproto/protobuf/field_mask"
)

// updateInstanceConfig updates the custom spanner instance config
func updateInstanceConfig(w io.Writer, projectID, userConfigID string) error {
	// projectID := "m
    
func updateInstanceConfig(w io.Writer, projectID, userConfigID string) error {
	// projectID := "my-project-id"
	// userConfigID := "custom-config", custom config names must start with the prefix “custom-”.

	// Add timeout to context.
	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Minute)
	defer cancel()

	adminClient, err := instance.NewInstanceAdminClient(ctx)
	if err != nil {
		return err
	}
	defer adminClient.Close()
	config, err := adminClient.GetInstanceConfig(ctx, &instancepb.GetInstanceConfigRequest{
		Name: fmt.Sprintf("projects/%s/instanceConfigs/%s", projectID, userConfigID),
	})
	if err != nil {
		return fmt.Errorf("updateInstanceConfig.GetInstanceConfig: %w", err)
	}
	config.DisplayName = "updated custom instance config"
	config.Labels["updated"] = "true"
	op, err := adminClient.UpdateInstanceConfig(ctx, &instancepb.UpdateInstanceConfigRequest{
		InstanceConfig: config,
		UpdateMask: &field_mask.FieldMask{
			Paths: []string{"display_name", "labels"},
		},
		ValidateOnly: false,
	})
	if err != nil {
		return err
	}
	fmt.Fprintf(w, "Waiting for update operation on %s to complete...\n", userConfigID)
	// Wait for the instance configuration creation to finish.
	i, err := op.Wait(ctx)
	if err != nil {
		return fmt.Errorf("Waiting for instance config creation to finish failed: %w", err)
	}
	// The instance configuration may not be ready to serve yet.
	if i.State != instancepb.InstanceConfig_READY {
		fmt.Fprintf(w, "InstanceConfig state is not READY yet. Got state %v\n", i.State)
	}
	fmt.Fprintf(w, "Updated instance configuration [%s]\n", config.Name)
	return nil
}