if constraint && comparable(V, true /* spec comparability */, nil, nil) {
			// V is comparable if we are at Go 1.20 or higher.
			if check == nil || check.allowVersion(atPos(pos), go1_20) { // atPos needed so that go/types generate passes
				return true
			}
			if cause != nil {
				*cause = check.sprintf("%s to %s comparable requires go1.20 or later", V, verb)
			}

		if constraint && comparable(V, true /* spec comparability */, nil, nil) {
			// V is comparable if we are at Go 1.20 or higher.
			if check == nil || check.allowVersion(atPos(pos), go1_20) { // atPos needed so that go/types generate passes
				return true
			}
			if cause != nil {
				*cause = check.sprintf("%s to %s comparable requires go1.20 or later", V, verb)
			}

			// error here as well (even though we could do it eagerly) because it's the same
			// error message.
			if check != nil {
				check.later(func() {
					if pos.IsKnown() && !check.allowVersion(atPos(pos), go1_14) || !Identical(m.typ, other.Type()) {
						err := check.newError(DuplicateDecl)
						err.addf(atPos(pos), "duplicate method %s", m.name)

			// error here as well (even though we could do it eagerly) because it's the same
			// error message.
			if check != nil {
				check.later(func() {
					if pos.IsValid() && !check.allowVersion(atPos(pos), go1_14) || !Identical(m.typ, other.Type()) {
						err := check.newError(DuplicateDecl)
						err.addf(atPos(pos), "duplicate method %s", m.name)

	// and collect the indices of generic parameters with untyped arguments.
	// Terminology: generic parameter = function parameter with a type-parameterized type
	u := newUnifier(tparams, targs, check.allowVersion(posn, go1_21))

	errorf := func(tpar, targ Type, arg *operand) {
		// provide a better error message if we can
		targs := u.inferred(tparams)
		if targs[0] == nil {

	// and collect the indices of generic parameters with untyped arguments.
	// Terminology: generic parameter = function parameter with a type-parameterized type
	u := newUnifier(tparams, targs, check.allowVersion(pos, go1_21))

	errorf := func(tpar, targ Type, arg *operand) {
		// provide a better error message if we can
		targs := u.inferred(tparams)
		if targs[0] == nil {

// literal is not compatible with the current language version.
func (check *Checker) langCompat(lit *ast.BasicLit) {
	s := lit.Value
	if len(s) <= 2 || check.allowVersion(lit, go1_13) {
		return
	}
	// len(s) > 2
	if strings.Contains(s, "_") {
		check.versionErrorf(lit, go1_13, "underscore in numeric literal")
		return
	}
	if s[0] != '0' {
		return
	}

// literal is not compatible with the current language version.
func (check *Checker) langCompat(lit *syntax.BasicLit) {
	s := lit.Value
	if len(s) <= 2 || check.allowVersion(lit, go1_13) {
		return
	}
	// len(s) > 2
	if strings.Contains(s, "_") {
		check.versionErrorf(lit, go1_13, "underscore in numeric literal")
		return
	}
	if s[0] != '0' {
		return
	}