cmd/go/internal/cache: use internal/godebug for three GODEBUGs

And register/document them.

Change-Id: If0f1cf3c09230e0f63d03c52e56e51a030468ab2
Reviewed-on: https://go-review.googlesource.com/c/go/+/487655
Auto-Submit: Dmitri Shuralyov <dmitshur@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Carlos Amedee <carlos@golang.org>
Reviewed-by: Bryan Mills <bcmills@google.com>
Run-TryBot: Dmitri Shuralyov <dmitshur@golang.org>

doc/godebug.md

@@ -182,6 +182,12 @@ Go 1.18 removed support for SHA1 in most X.509 certificates,
 controlled by the [`x509sha1` setting](/crypto/x509#InsecureAlgorithmError).
 This setting will be removed in a future release, Go 1.22 at the earliest.
 
+### Go 1.10
+
+Go 1.10 changed how build caching worked and added test caching, along
+with the [`gocacheverify`, `gocachehash`, and `gocachetest` settings](/cmd/go/#hdr-Build_and_test_caching).
+There is no plan to remove these settings.
+
 ### Go 1.6
 
 Go 1.6 introduced transparent support for HTTP/2,

src/cmd/go/internal/cache/cache.go

@@ -11,6 +11,7 @@ import (
 	"encoding/hex"
 	"errors"
 	"fmt"
+	"internal/godebug"
 	"io"
 	"io/fs"
 	"os"
@@ -115,21 +116,25 @@ var DebugTest = false
 
 func init() { initEnv() }
 
+var (
+	goCacheVerify = godebug.New("gocacheverify")
+	goDebugHash   = godebug.New("gocachehash")
+	goCacheTest   = godebug.New("gocachetest")
+)
+
 func initEnv() {
-	verify = false
-	debugHash = false
-	debug := strings.Split(os.Getenv("GODEBUG"), ",")
-	for _, f := range debug {
-		if f == "gocacheverify=1" {
+	if goCacheVerify.Value() == "1" {
+		goCacheVerify.IncNonDefault()
 		verify = true
 	}
-		if f == "gocachehash=1" {
+	if goDebugHash.Value() == "1" {
+		goDebugHash.IncNonDefault()
 		debugHash = true
 	}
-		if f == "gocachetest=1" {
+	if goCacheTest.Value() == "1" {
+		goCacheTest.IncNonDefault()
 		DebugTest = true
 	}
-	}
 }
 
 // Get looks up the action ID in the cache,

src/internal/godebugs/table.go

@@ -26,6 +26,9 @@ type Info struct {
 // (Otherwise the test in this package will fail.)
 var All = []Info{
 	{Name: "execerrdot", Package: "os/exec"},
+	{Name: "gocachehash", Package: "cmd/go"},
+	{Name: "gocachetest", Package: "cmd/go"},
+	{Name: "gocacheverify", Package: "cmd/go"},
 	{Name: "http2client", Package: "net/http"},
 	{Name: "http2debug", Package: "net/http", Opaque: true},
 	{Name: "http2server", Package: "net/http"},

src/runtime/metrics/doc.go

@@ -234,6 +234,18 @@ Below is the full list of supported metrics, ordered lexicographically.
 		The number of non-default behaviors executed by the os/exec
 		package due to a non-default GODEBUG=execerrdot=... setting.
 
+	/godebug/non-default-behavior/gocachehash:events
+		The number of non-default behaviors executed by the cmd/go
+		package due to a non-default GODEBUG=gocachehash=... setting.
+
+	/godebug/non-default-behavior/gocachetest:events
+		The number of non-default behaviors executed by the cmd/go
+		package due to a non-default GODEBUG=gocachetest=... setting.
+
+	/godebug/non-default-behavior/gocacheverify:events
+		The number of non-default behaviors executed by the cmd/go
+		package due to a non-default GODEBUG=gocacheverify=... setting.
+
 	/godebug/non-default-behavior/http2client:events
 		The number of non-default behaviors executed by the net/http
 		package due to a non-default GODEBUG=http2client=... setting.