internal/godebug: let interp fold settings so unused FIPS self-tests are removed

loader/goroot.go

@@ -245,6 +245,7 @@ func pathsToOverride(goMinor int, needsSyscallPackage bool) map[string]bool {
 		"internal/cm/":                false,
 		"internal/futex/":             false,
 		"internal/fuzz/":              false,
+		"internal/godebug/":           false,
 		"internal/itoa/":              false,
 		"internal/poll/":              false,
 		"internal/reflectlite/":       false,

src/internal/godebug/godebug.go

@@ -0,0 +1,83 @@
+// Package godebug is a simplified version of the upstream internal/godebug.
+// TinyGo only sees GODEBUG changes made with os.Setenv.
+package godebug
+
+import _ "unsafe" // go:linkname
+
+// A Setting is a single setting in the $GODEBUG environment variable.
+type Setting struct {
+	name string
+}
+
+// The current value of the $GODEBUG environment variable.
+var env string
+
+// New returns a new Setting for the $GODEBUG setting with the given name.
+// A name with a # prefix is an undocumented setting.
+func New(name string) *Setting {
+	return &Setting{name: name}
+}
+
+// Name returns the name of the setting.
+func (s *Setting) Name() string {
+	if s.name != "" && s.name[0] == '#' {
+		return s.name[1:]
+	}
+	return s.name
+}
+
+// Undocumented reports whether this is an undocumented setting.
+func (s *Setting) Undocumented() bool {
+	return s.name != "" && s.name[0] == '#'
+}
+
+// String returns a printable form for the setting: name=value.
+func (s *Setting) String() string {
+	return s.Name() + "=" + s.Value()
+}
+
+// IncNonDefault does nothing because TinyGo has no runtime/metrics support.
+func (s *Setting) IncNonDefault() {}
+
+// Value returns the current value for the GODEBUG setting s.
+func (s *Setting) Value() string {
+	return lookup(env, s.Name())
+}
+
+// lookup returns the value of name in s. Later settings win and a #pattern
+// suffix for bisect is ignored.
+func lookup(s, name string) string {
+	end := len(s)
+	eq := -1
+	for i := end - 1; i >= -1; i-- {
+		if i == -1 || s[i] == ',' {
+			if eq >= 0 && s[i+1:eq] == name {
+				arg := s[eq+1 : end]
+				for j := 0; j < len(arg); j++ {
+					if arg[j] == '#' {
+						return arg[:j]
+					}
+				}
+				return arg
+			}
+			eq = -1
+			end = i
+		} else if s[i] == '=' {
+			eq = i
+		}
+	}
+	return ""
+}
+
+//go:linkname setUpdate
+func setUpdate(update func(string, string))
+
+func init() {
+	setUpdate(update)
+}
+
+// update is called by the runtime when the GODEBUG environment variable
+// changes.
+func update(_, e string) {
+	env = e
+}