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: version3.go
    path of file: ./repos/terraform/internal/states/statefile
    
    the code of the file until where you have to start completion: // Copyright (c) HashiCorp, Inc.
// SPDX-License-Identifier: BUSL-1.1

package statefile

import (
	"encoding/json"
	"fmt"

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

func readStateV3(src []byte) (*File, tfdiags.Diagnostics) {
	var diags tfdiags.Diagnostics
	sV3 := &stateV3{}
	err := json.Unmarshal(src, sV3)
    
func prepareStateV3(sV3 *stateV3) (*File, tfdiags.Diagnostics) {
	var diags tfdiags.Diagnostics
	sV4, err := upgradeStateV3ToV4(sV3)
	if err != nil {
		diags = diags.Append(tfdiags.Sourceless(
			tfdiags.Error,
			upgradeFailed,
			fmt.Sprintf("Error upgrading state file format from version 3 to version 4: %s.", err),
		))
		return nil, diags
	}

	file, prepDiags := prepareStateV4(sV4)
	diags = diags.Append(prepDiags)
	return file, diags
}