// The Scopes mapping does not contain an entry for the
	// function body ([*ast.BlockStmt]); the function's scope is
	// associated with the [*ast.FuncType].
	//
	// The following node types may appear in Scopes:
	//
	//     *ast.File
	//     *ast.FuncType
	//     *ast.TypeSpec
	//     *ast.BlockStmt
	//     *ast.IfStmt
	//     *ast.SwitchStmt
	//     *ast.TypeSwitchStmt
	//     *ast.CaseClause

	// The Scopes mapping does not contain an entry for the
	// function body ([*ast.BlockStmt]); the function's scope is
	// associated with the [*ast.FuncType].
	//
	// The following node types may appear in Scopes:
	//
	//     *syntax.File
	//     *syntax.FuncType
	//     *syntax.TypeDecl
	//     *syntax.BlockStmt
	//     *syntax.IfStmt
	//     *syntax.SwitchStmt
	//     *syntax.CaseClause

		Walk(v, n.Key)
		Walk(v, n.Value)

	// Types
	case *ArrayType:
		if n.Len != nil {
			Walk(v, n.Len)
		}
		Walk(v, n.Elt)

	case *StructType:
		Walk(v, n.Fields)

	case *FuncType:
		if n.TypeParams != nil {
			Walk(v, n.TypeParams)
		}
		if n.Params != nil {
			Walk(v, n.Params)
		}
		if n.Results != nil {
			Walk(v, n.Results)
		}

	case *InterfaceType:

			if !isValid(typ.base) {
				return Typ[Invalid]
			}
			return typ
		}

		check.errorf(e0, NotAType, "%s is not a type", e0)
		check.use(e0)

	case *syntax.FuncType:
		typ := new(Signature)
		setDefType(def, typ)
		check.funcType(typ, nil, nil, e)
		return typ

	case *syntax.InterfaceType:
		typ := check.newInterface()
		setDefType(def, typ)
		check.interfaceType(typ, e, def)
		return typ

		typ.base = Typ[Invalid] // avoid nil base in invalid recursive type declaration
		setDefType(def, typ)
		typ.base = check.varType(e.X)
		return typ

	case *ast.FuncType:
		typ := new(Signature)
		setDefType(def, typ)
		check.funcType(typ, nil, e)
		return typ

	case *ast.InterfaceType:
		typ := check.newInterface()
		setDefType(def, typ)
		check.interfaceType(typ, e, def)
		return typ

				}
			}
		})
	}
}

// TestFuncType tests that an ast.FuncType with a nil Params field
// can be printed (per go/ast specification). Test case for issue 3870.
func TestFuncType(t *testing.T) {
	src := &ast.File{
		Name: &ast.Ident{Name: "p"},
		Decls: []ast.Decl{
			&ast.FuncDecl{
				Name: &ast.Ident{Name: "f"},
				Type: &ast.FuncType{},
			},
		},
	}

	var buf bytes.Buffer

// inadvertently copy a lock, by checking whether
// its receiver, parameters, or return values
// are locks.
func checkCopyLocksFunc(pass *analysis.Pass, name string, recv *ast.FieldList, typ *ast.FuncType) {
	if recv != nil && len(recv.List) > 0 {
		expr := recv.List[0].Type
		if path := lockPath(pass.Pkg, pass.TypesInfo.Types[expr].Type, nil); path != nil {

			r := TypeExpr(f, pkg, t.Results().At(i).Type())
			if r == nil {
				return nil
			}
			returns = append(returns, &ast.Field{
				Type: r,
			})
		}
		return &ast.FuncType{
			Params: &ast.FieldList{
				List: params,
			},
			Results: &ast.FieldList{
				List: returns,
			},
		}
	case interface{ Obj() *types.TypeName }: // *types.{Alias,Named,TypeParam}

var nopos syntax.Pos

// A rewriter implements rewriting the range-over-funcs in a given function.
type rewriter struct {
	pkg   *types2.Package
	info  *types2.Info
	sig   *types2.Signature
	outer *syntax.FuncType
	body  *syntax.BlockStmt

	// References to important types and values.
	any   types2.Object
	bool  types2.Object
	int   types2.Object
	true  types2.Object
	false types2.Object

	case *ArrayType:
		return filterType(t.Elt, f, export)
	case *StructType:
		if filterFieldList(t.Fields, f, export) {
			t.Incomplete = true
		}
		return len(t.Fields.List) > 0
	case *FuncType:
		b1 := filterParamList(t.Params, f, export)
		b2 := filterParamList(t.Results, f, export)
		return b1 || b2
	case *InterfaceType:
		if filterFieldList(t.Methods, f, export) {
			t.Incomplete = true
		}