internal/godebugs: test for use of IncNonDefault

A few recent godebugs are missing IncNonDefault uses.
Test for that, so that people remember to do it.
Filed bugs for the missing ones.

For #66215.
For #66216.
For #66217.

Change-Id: Ia3fd10fd108e1b003bb30a8bc2f83995c768fab6
Reviewed-on: https://go-review.googlesource.com/c/go/+/570275
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Damien Neil <dneil@google.com>

9 files changed, 100 insertions, 49 deletions

diff --git a/src/cmd/go/internal/cache/cache.go b/src/cmd/go/internal/cache/cache.go
index 14b2deccd4..c3442eccbf 100644
--- a/src/cmd/go/internal/cache/cache.go
+++ b/src/cmd/go/internal/cache/cache.go
@@ -159,22 +159,22 @@ var DebugTest = false
 func init() { initEnv() }
 
 var (
-	goCacheVerify = godebug.New("gocacheverify")
-	goDebugHash   = godebug.New("gocachehash")
-	goCacheTest   = godebug.New("gocachetest")
+	gocacheverify = godebug.New("gocacheverify")
+	gocachehash   = godebug.New("gocachehash")
+	gocachetest   = godebug.New("gocachetest")
 )
 
 func initEnv() {
-	if goCacheVerify.Value() == "1" {
-		goCacheVerify.IncNonDefault()
+	if gocacheverify.Value() == "1" {
+		gocacheverify.IncNonDefault()
 		verify = true
 	}
-	if goDebugHash.Value() == "1" {
-		goDebugHash.IncNonDefault()
+	if gocachehash.Value() == "1" {
+		gocachehash.IncNonDefault()
 		debugHash = true
 	}
-	if goCacheTest.Value() == "1" {
-		goCacheTest.IncNonDefault()
+	if gocachetest.Value() == "1" {
+		gocachetest.IncNonDefault()
 		DebugTest = true
 	}
 }
diff --git a/src/crypto/x509/x509.go b/src/crypto/x509/x509.go
index f33283b559..636a345eef 100644
--- a/src/crypto/x509/x509.go
+++ b/src/crypto/x509/x509.go
@@ -1101,7 +1101,7 @@ func isIA5String(s string) error {
 	return nil
 }
 
-var usePoliciesField = godebug.New("x509usepolicies")
+var x509usepolicies = godebug.New("x509usepolicies")
 
 func buildCertExtensions(template *Certificate, subjectIsEmpty bool, authorityKeyId []byte, subjectKeyId []byte) (ret []pkix.Extension, err error) {
 	ret = make([]pkix.Extension, 10 /* maximum number of elements. */)
@@ -1188,7 +1188,7 @@ func buildCertExtensions(template *Certificate, subjectIsEmpty bool, authorityKe
 		n++
 	}
 
-	usePolicies := usePoliciesField.Value() == "1"
+	usePolicies := x509usepolicies.Value() == "1"
 	if ((!usePolicies && len(template.PolicyIdentifiers) > 0) || (usePolicies && len(template.Policies) > 0)) &&
 		!oidInExtensions(oidExtensionCertificatePolicies, template.ExtraExtensions) {
 		ret[n], err = marshalCertificatePolicies(template.Policies, template.PolicyIdentifiers)
@@ -1381,8 +1381,8 @@ func marshalCertificatePolicies(policies []OID, policyIdentifiers []asn1.ObjectI
 
 	b := cryptobyte.NewBuilder(make([]byte, 0, 128))
 	b.AddASN1(cryptobyte_asn1.SEQUENCE, func(child *cryptobyte.Builder) {
-		if usePoliciesField.Value() == "1" {
-			usePoliciesField.IncNonDefault()
+		if x509usepolicies.Value() == "1" {
+			x509usepolicies.IncNonDefault()
 			for _, v := range policies {
 				child.AddASN1(cryptobyte_asn1.SEQUENCE, func(child *cryptobyte.Builder) {
 					child.AddASN1(cryptobyte_asn1.OBJECT_IDENTIFIER, func(child *cryptobyte.Builder) {
diff --git a/src/internal/godebug/godebug.go b/src/internal/godebug/godebug.go
index 36bfeaccc4..0756d313e6 100644
--- a/src/internal/godebug/godebug.go
+++ b/src/internal/godebug/godebug.go
@@ -22,8 +22,23 @@
 //	}
 //
 // Each time a non-default setting causes a change in program behavior,
-// code should call [Setting.IncNonDefault] to increment a counter that can
-// be reported by [runtime/metrics.Read].
+// code must call [Setting.IncNonDefault] to increment a counter that can
+// be reported by [runtime/metrics.Read]. The call must only happen when
+// the program executes a non-default behavior, not just when the setting
+// is set to a non-default value. This is occasionally (but very rarely)
+// infeasible, in which case the internal/godebugs table entry must set
+// Opaque: true, and the documentation in doc/godebug.md should
+// mention that metrics are unavailable.
+//
+// Conventionally, the global variable representing a godebug is named
+// for the godebug itself, with no case changes:
+//
+//	var gotypesalias = godebug.New("gotypesalias") // this
+//	var goTypesAlias = godebug.New("gotypesalias") // NOT THIS
+//
+// The test in internal/godebugs that checks for use of IncNonDefault
+// requires the use of this convention.
+//
 // Note that counters used with IncNonDefault must be added to
 // various tables in other packages. See the [Setting.IncNonDefault]
 // documentation for details.
@@ -70,6 +85,11 @@ type value struct {
 // To disable that panic for access to an undocumented setting,
 // prefix the name with a #, as in godebug.New("#gofsystrace").
 // The # is a signal to New but not part of the key used in $GODEBUG.
+//
+// Note that almost all settings should arrange to call [IncNonDefault] precisely
+// when program behavior is changing from the default due to the setting
+// (not just when the setting is different, but when program behavior changes).
+// See the [internal/godebug] package comment for more.
 func New(name string) *Setting {
 	return &Setting{name: name}
 }
diff --git a/src/internal/godebugs/godebugs_test.go b/src/internal/godebugs/godebugs_test.go
index a1cb8d492a..046193b5c6 100644
--- a/src/internal/godebugs/godebugs_test.go
+++ b/src/internal/godebugs/godebugs_test.go
@@ -8,12 +8,17 @@ import (
 	"internal/godebugs"
 	"internal/testenv"
 	"os"
+	"os/exec"
+	"path/filepath"
+	"regexp"
 	"runtime"
 	"strings"
 	"testing"
 )
 
 func TestAll(t *testing.T) {
+	testenv.MustHaveGoBuild(t)
+
 	data, err := os.ReadFile("../../../doc/godebug.md")
 	if err != nil {
 		if os.IsNotExist(err) && (testenv.Builder() == "" || runtime.GOOS != "linux") {
@@ -23,6 +28,8 @@ func TestAll(t *testing.T) {
 	}
 	doc := string(data)
 
+	incs := incNonDefaults(t)
+
 	last := ""
 	for _, info := range godebugs.All {
 		if info.Name <= last {
@@ -42,5 +49,46 @@ func TestAll(t *testing.T) {
 		if !strings.Contains(doc, "`"+info.Name+"`") {
 			t.Errorf("Name=%s not documented in doc/godebug.md", info.Name)
 		}
+		if !info.Opaque && !incs[info.Name] {
+			t.Errorf("Name=%s missing IncNonDefault calls; see 'go doc internal/godebug'", info.Name)
+		}
+	}
+}
+
+var incNonDefaultRE = regexp.MustCompile(`([\pL\p{Nd}_]+)\.IncNonDefault\(\)`)
+
+func incNonDefaults(t *testing.T) map[string]bool {
+	// Build list of all files importing internal/godebug.
+	// Tried a more sophisticated search in go list looking for
+	// imports containing "internal/godebug", but that turned
+	// up a bug in go list instead. #66218
+	out, err := exec.Command("go", "list", "-f={{.Dir}}", "std", "cmd").CombinedOutput()
+	if err != nil {
+		t.Fatalf("go list: %v\n%s", err, out)
+	}
+
+	seen := map[string]bool{}
+	for _, dir := range strings.Split(string(out), "\n") {
+		if dir == "" {
+			continue
+		}
+		files, err := os.ReadDir(dir)
+		if err != nil {
+			t.Fatal(err)
+		}
+		for _, file := range files {
+			name := file.Name()
+			if !strings.HasSuffix(name, ".go") || strings.HasSuffix(name, "_test.go") {
+				continue
+			}
+			data, err := os.ReadFile(filepath.Join(dir, name))
+			if err != nil {
+				t.Fatal(err)
+			}
+			for _, m := range incNonDefaultRE.FindAllSubmatch(data, -1) {
+				seen[string(m[1])] = true
+			}
+		}
 	}
+	return seen
 }
diff --git a/src/internal/godebugs/table.go b/src/internal/godebugs/table.go
index d5ac707a18..c11f708dd9 100644
--- a/src/internal/godebugs/table.go
+++ b/src/internal/godebugs/table.go
@@ -29,14 +29,14 @@ var All = []Info{
 	{Name: "gocachehash", Package: "cmd/go"},
 	{Name: "gocachetest", Package: "cmd/go"},
 	{Name: "gocacheverify", Package: "cmd/go"},
-	{Name: "gotypesalias", Package: "go/types"},
+	{Name: "gotypesalias", Package: "go/types", Opaque: true}, // bug #66216: remove Opaque
 	{Name: "http2client", Package: "net/http"},
 	{Name: "http2debug", Package: "net/http", Opaque: true},
 	{Name: "http2server", Package: "net/http"},
 	{Name: "httplaxcontentlength", Package: "net/http", Changed: 22, Old: "1"},
 	{Name: "httpmuxgo121", Package: "net/http", Changed: 22, Old: "1"},
 	{Name: "installgoroot", Package: "go/build"},
-	{Name: "jstmpllitinterp", Package: "html/template"},
+	{Name: "jstmpllitinterp", Package: "html/template", Opaque: true}, // bug #66217: remove Opaque
 	//{Name: "multipartfiles", Package: "mime/multipart"},
 	{Name: "multipartmaxheaders", Package: "mime/multipart"},
 	{Name: "multipartmaxparts", Package: "mime/multipart"},
@@ -49,8 +49,8 @@ var All = []Info{
 	{Name: "tlsmaxrsasize", Package: "crypto/tls"},
 	{Name: "tlsrsakex", Package: "crypto/tls", Changed: 22, Old: "1"},
 	{Name: "tlsunsafeekm", Package: "crypto/tls", Changed: 22, Old: "1"},
-	{Name: "winreadlinkvolume", Package: "os", Changed: 22, Old: "0"},
-	{Name: "winsymlink", Package: "os", Changed: 22, Old: "0"},
+	{Name: "winreadlinkvolume", Package: "os", Changed: 22, Old: "0", Opaque: true}, // bug #66215: remove Opaque
+	{Name: "winsymlink", Package: "os", Changed: 22, Old: "0", Opaque: true},        // bug #66215: remove Opaque
 	{Name: "x509sha1", Package: "crypto/x509"},
 	{Name: "x509usefallbackroots", Package: "crypto/x509"},
 	{Name: "x509usepolicies", Package: "crypto/x509"},
diff --git a/src/mime/multipart/formdata.go b/src/mime/multipart/formdata.go
index 85bad2a4cb..e0a63a66ae 100644
--- a/src/mime/multipart/formdata.go
+++ b/src/mime/multipart/formdata.go
@@ -34,8 +34,8 @@ func (r *Reader) ReadForm(maxMemory int64) (*Form, error) {
 }
 
 var (
-	multipartFiles    = godebug.New("#multipartfiles") // TODO: document and remove #
-	multipartMaxParts = godebug.New("multipartmaxparts")
+	multipartfiles    = godebug.New("#multipartfiles") // TODO: document and remove #
+	multipartmaxparts = godebug.New("multipartmaxparts")
 )
 
 func (r *Reader) readForm(maxMemory int64) (_ *Form, err error) {
@@ -46,15 +46,15 @@ func (r *Reader) readForm(maxMemory int64) (_ *Form, err error) {
 	)
 	numDiskFiles := 0
 	combineFiles := true
-	if multipartFiles.Value() == "distinct" {
+	if multipartfiles.Value() == "distinct" {
 		combineFiles = false
-		// multipartFiles.IncNonDefault() // TODO: uncomment after documenting
+		// multipartfiles.IncNonDefault() // TODO: uncomment after documenting
 	}
 	maxParts := 1000
-	if s := multipartMaxParts.Value(); s != "" {
+	if s := multipartmaxparts.Value(); s != "" {
 		if v, err := strconv.Atoi(s); err == nil && v >= 0 {
 			maxParts = v
-			multipartMaxParts.IncNonDefault()
+			multipartmaxparts.IncNonDefault()
 		}
 	}
 	maxHeaders := maxMIMEHeaders()
diff --git a/src/mime/multipart/multipart.go b/src/mime/multipart/multipart.go
index da1f45810e..00a7e5fe46 100644
--- a/src/mime/multipart/multipart.go
+++ b/src/mime/multipart/multipart.go
@@ -347,15 +347,15 @@ type Reader struct {
 // including header keys, values, and map overhead.
 const maxMIMEHeaderSize = 10 << 20
 
-// multipartMaxHeaders is the maximum number of header entries NextPart will return,
+// multipartmaxheaders is the maximum number of header entries NextPart will return,
 // as well as the maximum combined total of header entries Reader.ReadForm will return
 // in FileHeaders.
-var multipartMaxHeaders = godebug.New("multipartmaxheaders")
+var multipartmaxheaders = godebug.New("multipartmaxheaders")
 
 func maxMIMEHeaders() int64 {
-	if s := multipartMaxHeaders.Value(); s != "" {
+	if s := multipartmaxheaders.Value(); s != "" {
 		if v, err := strconv.ParseInt(s, 10, 64); err == nil && v >= 0 {
-			multipartMaxHeaders.IncNonDefault()
+			multipartmaxheaders.IncNonDefault()
 			return v
 		}
 	}
diff --git a/src/net/http/transfer.go b/src/net/http/transfer.go
index 255e8bc45a..ee2107c418 100644
--- a/src/net/http/transfer.go
+++ b/src/net/http/transfer.go
@@ -1043,7 +1043,7 @@ func (bl bodyLocked) Read(p []byte) (n int, err error) {
 	return bl.b.readLocked(p)
 }
 
-var laxContentLength = godebug.New("httplaxcontentlength")
+var httplaxcontentlength = godebug.New("httplaxcontentlength")
 
 // parseContentLength checks that the header is valid and then trims
 // whitespace. It returns -1 if no value is set otherwise the value
@@ -1057,8 +1057,8 @@ func parseContentLength(clHeaders []string) (int64, error) {
 	// The Content-Length must be a valid numeric value.
 	// See: https://datatracker.ietf.org/doc/html/rfc2616/#section-14.13
 	if cl == "" {
-		if laxContentLength.Value() == "1" {
-			laxContentLength.IncNonDefault()
+		if httplaxcontentlength.Value() == "1" {
+			httplaxcontentlength.IncNonDefault()
 			return -1, nil
 		}
 		return 0, badStringError("invalid empty Content-Length", cl)
diff --git a/src/runtime/metrics/doc.go b/src/runtime/metrics/doc.go
index e63599e0d9..e1b3387c13 100644
--- a/src/runtime/metrics/doc.go
+++ b/src/runtime/metrics/doc.go
@@ -246,10 +246,6 @@ Below is the full list of supported metrics, ordered lexicographically.
 		The number of non-default behaviors executed by the cmd/go
 		package due to a non-default GODEBUG=gocacheverify=... setting.
 
-	/godebug/non-default-behavior/gotypesalias:events
-		The number of non-default behaviors executed by the go/types
-		package due to a non-default GODEBUG=gotypesalias=... 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.
@@ -271,11 +267,6 @@ Below is the full list of supported metrics, ordered lexicographically.
 		The number of non-default behaviors executed by the go/build
 		package due to a non-default GODEBUG=installgoroot=... setting.
 
-	/godebug/non-default-behavior/jstmpllitinterp:events
-		The number of non-default behaviors executed by
-		the html/template package due to a non-default
-		GODEBUG=jstmpllitinterp=... setting.
-
 	/godebug/non-default-behavior/multipartmaxheaders:events
 		The number of non-default behaviors executed by
 		the mime/multipart package due to a non-default
@@ -319,14 +310,6 @@ Below is the full list of supported metrics, ordered lexicographically.
 		The number of non-default behaviors executed by the crypto/tls
 		package due to a non-default GODEBUG=tlsunsafeekm=... setting.
 
-	/godebug/non-default-behavior/winreadlinkvolume:events
-		The number of non-default behaviors executed by the os package
-		due to a non-default GODEBUG=winreadlinkvolume=... setting.
-
-	/godebug/non-default-behavior/winsymlink:events
-		The number of non-default behaviors executed by the os package
-		due to a non-default GODEBUG=winsymlink=... setting.
-
 	/godebug/non-default-behavior/x509sha1:events
 		The number of non-default behaviors executed by the crypto/x509
 		package due to a non-default GODEBUG=x509sha1=... setting.