hash: do not salt with Go runtime version

cache/hash.go

@@ -11,7 +11,6 @@ import (
 	"hash"
 	"io"
 	"os"
-	"runtime"
 	"strings"
 	"sync"
 )
@@ -29,22 +28,6 @@ type Hash struct {
 	buf  *bytes.Buffer // for verify
 }
 
-// hashSalt is a salt string added to the beginning of every hash
-// created by NewHash. Using the Go version makes sure that different
-// versions of the go command (or even different Git commits during
-// work on the development branch) do not address the same cache
-// entries, so that a bug in one version does not affect the execution
-// of other versions. This salt will result in additional ActionID files
-// in the cache, but not additional copies of the large output files,
-// which are still addressed by unsalted SHA256.
-//
-// We strip any GOEXPERIMENTs the go tool was built with from this
-// version string on the assumption that they shouldn't affect go tool
-// execution. This allows bootstrapping to converge faster: dist builds
-// go_bootstrap without any experiments, so by stripping experiments
-// go_bootstrap and the final go binary will use the same salt.
-var hashSalt = []byte(stripExperiment(runtime.Version()))
-
 // stripExperiment strips any GOEXPERIMENT configuration from the Go
 // version string.
 func stripExperiment(version string) string {
@@ -81,7 +64,6 @@ func NewHash(name string) *Hash {
 	if debugHash {
 		fmt.Fprintf(os.Stderr, "HASH[%s]\n", h.name)
 	}
-	h.Write(hashSalt)
 	if verify {
 		h.buf = new(bytes.Buffer)
 	}

cache/hash_test.go

@@ -11,12 +11,6 @@ import (
 )
 
 func TestHash(t *testing.T) {
-	oldSalt := hashSalt
-	hashSalt = nil
-	defer func() {
-		hashSalt = oldSalt
-	}()
-
 	h := NewHash("alice")
 	h.Write([]byte("hello world"))
 	sum := fmt.Sprintf("%x", h.Sum())