if typ == nil || seen[typ] {
		return nil
	}
	if seen == nil {
		seen = make(map[types.Type]bool)
	}
	seen[typ] = true

	if tpar, ok := aliases.Unalias(typ).(*types.TypeParam); ok {
		terms, err := typeparams.StructuralTerms(tpar)
		if err != nil {
			return nil // invalid type
		}
		for _, term := range terms {
			subpath := lockPath(tpkg, term.Type(), seen)

		// TODO(gri) report detailed failure cause for better error messages
		var key, elem Type // key != nil: we must have all maps
		mode := variable   // non-maps result mode
		// TODO(gri) factor out closure and use it for non-typeparam cases as well
		if typ.typeSet().underIs(func(u Type) bool {
			l := int64(-1) // valid if >= 0
			var k, e Type  // k is only set for maps
			switch t := u.(type) {
			case *Basic:
				if isString(t) {

		// TODO(gri) report detailed failure cause for better error messages
		var key, elem Type // key != nil: we must have all maps
		mode := variable   // non-maps result mode
		// TODO(gri) factor out closure and use it for non-typeparam cases as well
		if typ.typeSet().underIs(func(u Type) bool {
			l := int64(-1) // valid if >= 0
			var k, e Type  // k is only set for maps
			switch t := u.(type) {
			case *Basic:
				if isString(t) {

	if check != nil {
		check.error(atPos(pos), WrongTypeArgCount, msg)
		return false
	}

	panic(fmt.Sprintf("%v: %s", pos, msg))
}

func (check *Checker) verify(pos syntax.Pos, tparams []*TypeParam, targs []Type, ctxt *Context) (int, error) {
	smap := makeSubstMap(tparams, targs)
	for i, tpar := range tparams {
		// Ensure that we have a (possibly implicit) interface as type bound (go.dev/issue/51048).
		tpar.iface()

		named.underlying = Typ[Invalid]
	}
}

func (check *Checker) collectTypeParams(dst **TypeParamList, list []*syntax.Field) {
	tparams := make([]*TypeParam, len(list))

	// Declare type parameters up-front.
	// The scope of type parameters starts at the beginning of the type parameter
	// list (so we can have mutually recursive parameterized type bounds).

		var n int
		for x, tv := range types {
			if x, _ := x.(*ast.CallExpr); x != nil {
				// there must be exactly one CallExpr which is the P(val) conversion
				n++
				tpar, _ := tv.Type.(*TypeParam)
				if tpar == nil {
					t.Fatalf("%s: got type %s, want type parameter", ExprString(x), tv.Type)
				}
				if name := tpar.Obj().Name(); name != "P" {

		var n int
		for x, tv := range types {
			if x, _ := x.(*syntax.CallExpr); x != nil {
				// there must be exactly one CallExpr which is the P(val) conversion
				n++
				tpar, _ := tv.Type.(*TypeParam)
				if tpar == nil {
					t.Fatalf("%s: got type %s, want type parameter", ExprString(x), tv.Type)
				}
				if name := tpar.Obj().Name(); name != "P" {

	if check != nil {
		check.error(atPos(pos), WrongTypeArgCount, msg)
		return false
	}

	panic(fmt.Sprintf("%v: %s", pos, msg))
}

func (check *Checker) verify(pos token.Pos, tparams []*TypeParam, targs []Type, ctxt *Context) (int, error) {
	smap := makeSubstMap(tparams, targs)
	for i, tpar := range tparams {
		// Ensure that we have a (possibly implicit) interface as type bound (go.dev/issue/51048).
		tpar.iface()

	"termlist.go":      nil,
	"termlist_test.go": nil,
	"tuple.go":         nil,
	"typelists.go":     nil,
	"typeset.go":       func(f *ast.File) { fixTokenPos(f); renameSelectors(f, "Trace->_Trace") },
	"typeparam.go":     nil,
	"typeterm_test.go": nil,
	"typeterm.go":      nil,
	"typestring.go":    nil,
	"under.go":         nil,
	"unify.go":         fixSprintf,
	"universe.go":      fixGlobalTypVarDecl,

	imports       []*PkgName                // list of imported packages
	dotImportMap  map[dotImportKey]*PkgName // maps dot-imported objects to the package they were dot-imported through
	recvTParamMap map[*ast.Ident]*TypeParam // maps blank receiver type parameters to their type
	brokenAliases map[*TypeName]bool        // set of aliases with broken (not yet determined) types
	unionTypeSets map[*Union]*_TypeSet      // computed type sets for union types