a.actionID = actionHash
	actionID := buildid.HashToString(actionHash)
	if a.json != nil {
		a.json.ActionID = actionID
	}
	contentID := actionID // temporary placeholder, likely unique
	a.buildID = actionID + buildIDSeparator + contentID

	// Executable binaries also record the main build ID in the middle.
	// See "Build IDs" comment above.
	if a.Mode == "link" {
		mainpkg := a.Deps[0]

	if err != nil {
		t.Fatal(err)
	}
	name := f.Name()
	fmt.Fprintf(f, "hello world")
	defer os.Remove(name)
	if err := f.Close(); err != nil {
		t.Fatal(err)
	}

	var h ActionID // make sure hash result is assignable to ActionID
	h, err = FileHash(name)
	if err != nil {
		t.Fatal(err)
	}
	sum := fmt.Sprintf("%x", h)
	want := "b94d27b9934d3e08a52e52d7da7dabfac484efe37a5380ee9088f7ace2efcde9"
	if sum != want {

			t.Fatalf("addIndexEntry: %v", err)
		}
		id := ActionID(dummyID(i))
		entry, err := c.Get(id)
		if err != nil {
			t.Fatalf("Get(%x): %v", id, err)
		}
		if entry.OutputID != dummyID(i*99) || entry.Size != int64(i)*101 {
			t.Errorf("Get(%x) = %x, %d, want %x, %d", id, entry.OutputID, entry.Size, dummyID(i*99), int64(i)*101)
		}
	}
	for i := 0; i < n; i++ {
		id := ActionID(dummyID(i))
		entry, err := c.Get(id)
		if err != nil {

	"strconv"
	"strings"
	"time"

	"cmd/go/internal/lockedfile"
	"cmd/go/internal/mmap"
)

// An ActionID is a cache action key, the hash of a complete description of a
// repeatable computation (command line, environment variables,
// input file contents, executable contents).
type ActionID [HashSize]byte

// An OutputID is a cache output key, the hash of an output of a computation.
type OutputID [HashSize]byte

	ID int64

	// Command is the type of request.
	// The cmd/go tool will only send commands that were declared
	// as supported by the child.
	Command ProgCmd

	// ActionID is non-nil for get and puts.
	ActionID []byte `json:",omitempty"` // or nil if not used

	// ObjectID is set for Type "put" and "output-file".
	ObjectID []byte `json:",omitempty"` // or nil if not used

}

// Subkey returns an action ID corresponding to mixing a parent
// action ID with a string description of the subkey.
func Subkey(parent ActionID, desc string) ActionID {
	h := sha256.New()
	h.Write([]byte("subkey:"))
	h.Write(parent[:])
	h.Write([]byte(desc))
	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()

type Module struct {
	modroot string
	d       *decoder
	n       int // number of packages
}

// moduleHash returns an ActionID corresponding to the state of the module
// located at filesystem path modroot.
func moduleHash(modroot string, ismodcache bool) (cache.ActionID, error) {
	// We expect modules stored within the module cache to be checksummed and
	// immutable, and we expect released modules within GOROOT to change only

	if err != nil {
		log.Fatal(err)
	}
	matches, hash, err := buildid.FindAndHash(f, id, 0)
	f.Close()
	if err != nil {
		log.Fatal(err)
	}

	// <= go 1.7 doesn't embed the contentID or actionID, so no slash is present
	if !strings.Contains(id, "/") {
		log.Fatalf("%s: build ID is a legacy format...binary too old for this tool", file)
	}

	newID := id[:strings.LastIndex(id, "/")] + "/" + buildid.HashToString(hash)

func testAndInputKey(testID, testInputsID cache.ActionID) cache.ActionID {
	return cache.Subkey(testID, fmt.Sprintf("inputs:%x", testInputsID))
}

func (c *runCache) saveOutput(a *work.Action) {
	if c.id1 == (cache.ActionID{}) && c.id2 == (cache.ActionID{}) {
		return
	}

	// See comment about two-level lookup in tryCacheWithID above.

	Objdir   string         // directory for intermediate objects
	Target   string         // goal of the action: the created package or executable
	built    string         // the actual created package or executable
	actionID cache.ActionID // cache ID of action input
	buildID  string         // build ID of action output

	VetxOnly  bool       // Mode=="vet": only being called to supply info about dependencies