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: hash.go
    path of file: ./repos/golangci-lint/internal/cache
    
    the code of the file until where you have to start completion: // Copyright 2017 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package cache

import (
	"bytes"
	"crypto/sha256"
	"fmt"
	"hash"
	"io"
	"os"
	"sync"
)

var debugHash = false // set when GODEBUG=gocachehash=1

// HashSize is the number of bytes in a hash.
const HashSize = 32

// A Hash provides access to the canonical hash function used to index the cache.
// The current implementation uses salted SHA256, but clients must not assume this.
type Hash struct {
	h    hash.Hash
	name string        // for
    
func Subkey(parent ActionID, desc string) (ActionID, error) {
	h := sha256.New()
	const subkeyPrefix = "subkey:"
	if n, err := h.Write([]byte(subkeyPrefix)); n != len(subkeyPrefix) {
		return ActionID{}, fmt.Errorf("wrote %d/%d bytes of subkey prefix with error %s", n, len(subkeyPrefix), err)
	}
	if n, err := h.Write(parent[:]); n != len(parent) {
		return ActionID{}, fmt.Errorf("wrote %d/%d bytes of parent with error %s", n, len(parent), err)
	}
	if n, err := h.Write([]byte(desc)); n != len(desc) {
		return ActionID{}, fmt.Errorf("wrote %d/%d bytes of desc with error %s", n, len(desc), err)
	}

	var out ActionID
	h.Sum(out[:0])
	if debugHash {
		fmt.Fprintf(os.Stderr, "HASH subkey %x %q = %x\n", parent, desc, out)
	}
	if verify {
		hashDebug.Lock()
		hashDebug.m[out] = fmt.Sprintf("subkey %x %q", parent, desc)
		hashDebug.Unlock()
	}
	return out, nil
}