if err := cmd.Run(); err != nil {
		t.Fatal(cmd, ":", err)
	}
	_, lang, ok := strings.Cut(doc.String(), "# Script Language\n\n")
	if !ok {
		t.Fatalf("%q did not include Script Language section", cmd)
	}
	lang, _, ok = strings.Cut(lang, "\n\nvar ")
	if !ok {
		t.Fatalf("%q did not include vars after Script Language section", cmd)
	}
	args.Language = lang

	tmpl := template.Must(template.New("README").Parse(readmeTmpl[1:]))

}

// ParseLangFlag verifies that the -lang flag holds a valid value, and
// exits if not. It initializes data used by AllowsGoVersion.
func ParseLangFlag() {
	if base.Flag.Lang == "" {
		return
	}

	var err error
	langWant, err = parseLang(base.Flag.Lang)
	if err != nil {
		log.Fatalf("invalid value %q for -lang: %v", base.Flag.Lang, err)
	}

	if def := currentLang(); base.Flag.Lang != def {
		defVers, err := parseLang(def)

// say "go 1.21", but Go 1.21rc1 will not handle files that say "go 1.21.0".
func IsLang(x string) bool {
	return gover.IsLang(x)
}

// Lang returns the Go language version. For example, Lang("1.2.3") == "1.2".
func Lang(x string) string {
	return gover.Lang(x)
}

// IsPrerelease reports whether v denotes a Go prerelease version.
func IsPrerelease(x string) bool {
	return gover.Parse(x).Kind != ""
}

type goVersion string

// asGoVersion returns v as a goVersion (e.g., "go1.20.1" becomes "go1.20").
// If v is not a valid Go version, the result is the empty string.
func asGoVersion(v string) goVersion {
	return goVersion(version.Lang(v))
}

// isValid reports whether v is a valid Go version.
func (v goVersion) isValid() bool {
	return v != ""
}

// cmp returns -1, 0, or +1 depending on whether x < y, x == y, or x > y,

	{"1.19alpha3", "1.19beta2", -1},
	{"1.19beta2", "1.19rc1", -1},
	{"1.1", "1.99999999999999998", -1},
	{"1.99999999999999998", "1.99999999999999999", -1},
}

func TestLang(t *testing.T) { test1(t, langTests, "Lang", Lang) }

var langTests = []testCase1[string, string]{
	{"1.2rc3", "1.2"},
	{"1.2.3", "1.2"},
	{"1.2", "1.2"},
	{"1", "1"},
	{"1.999testmod", "1.999"},
}

	// Failing that we'll take the latest release.
	latest := ""
	for i := len(list) - 1; i >= 0; i-- {
		v := list[i]
		if gover.Compare(v, need) < 0 {
			break
		}
		if gover.Lang(latest) == gover.Lang(v) {
			continue
		}
		newer := latest
		latest = v
		if newer != "" && !gover.IsPrerelease(newer) {
			// latest is the last patch release of Go 1.X, and we saw a non-prerelease of Go 1.(X+1),