hugo

exec.go (32224B)

 // Copyright 2011 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
 package template
 
 import (
 	"errors"
 	"fmt"
 	"github.com/gohugoio/hugo/tpl/internal/go_templates/fmtsort"
 	"github.com/gohugoio/hugo/tpl/internal/go_templates/texttemplate/parse"
 	"io"
 	"reflect"
 	"runtime"
 	"strings"
 )
 
 // maxExecDepth specifies the maximum stack depth of templates within
 // templates. This limit is only practically reached by accidentally
 // recursive template invocations. This limit allows us to return
 // an error instead of triggering a stack overflow.
 var maxExecDepth = initMaxExecDepth()
 
 func initMaxExecDepth() int {
 	if runtime.GOARCH == "wasm" {
 		return 1000
 	}
 	return 100000
 }
 
 // state represents the state of an execution. It's not part of the
 // template so that multiple executions of the same template
 // can execute in parallel.
 type stateOld struct {
 	tmpl  *Template
 	wr    io.Writer
 	node  parse.Node // current node, for errors
 	vars  []variable // push-down stack of variable values.
 	depth int        // the height of the stack of executing templates.
 }
 
 // variable holds the dynamic value of a variable such as $, $x etc.
 type variable struct {
 	name  string
 	value reflect.Value
 }
 
 // push pushes a new variable on the stack.
 func (s *state) push(name string, value reflect.Value) {
 	s.vars = append(s.vars, variable{name, value})
 }
 
 // mark returns the length of the variable stack.
 func (s *state) mark() int {
 	return len(s.vars)
 }
 
 // pop pops the variable stack up to the mark.
 func (s *state) pop(mark int) {
 	s.vars = s.vars[0:mark]
 }
 
 // setVar overwrites the last declared variable with the given name.
 // Used by variable assignments.
 func (s *state) setVar(name string, value reflect.Value) {
 	for i := s.mark() - 1; i >= 0; i-- {
 		if s.vars[i].name == name {
 			s.vars[i].value = value
 			return
 		}
 	}
 	s.errorf("undefined variable: %s", name)
 }
 
 // setTopVar overwrites the top-nth variable on the stack. Used by range iterations.
 func (s *state) setTopVar(n int, value reflect.Value) {
 	s.vars[len(s.vars)-n].value = value
 }
 
 // varValue returns the value of the named variable.
 func (s *state) varValue(name string) reflect.Value {
 	for i := s.mark() - 1; i >= 0; i-- {
 		if s.vars[i].name == name {
 			return s.vars[i].value
 		}
 	}
 	s.errorf("undefined variable: %s", name)
 	return zero
 }
 
 var zero reflect.Value
 
 type missingValType struct{}
 
 var missingVal = reflect.ValueOf(missingValType{})
 
 // at marks the state to be on node n, for error reporting.
 func (s *state) at(node parse.Node) {
 	s.node = node
 }
 
 // doublePercent returns the string with %'s replaced by %%, if necessary,
 // so it can be used safely inside a Printf format string.
 func doublePercent(str string) string {
 	return strings.ReplaceAll(str, "%", "%%")
 }
 
 // TODO: It would be nice if ExecError was more broken down, but
 // the way ErrorContext embeds the template name makes the
 // processing too clumsy.
 
 // ExecError is the custom error type returned when Execute has an
 // error evaluating its template. (If a write error occurs, the actual
 // error is returned; it will not be of type ExecError.)
 type ExecError struct {
 	Name string // Name of template.
 	Err  error  // Pre-formatted error.
 }
 
 func (e ExecError) Error() string {
 	return e.Err.Error()
 }
 
 func (e ExecError) Unwrap() error {
 	return e.Err
 }
 
 // errorf records an ExecError and terminates processing.
 func (s *state) errorf(format string, args ...any) {
 	name := doublePercent(s.tmpl.Name())
 	if s.node == nil {
 		format = fmt.Sprintf("template: %s: %s", name, format)
 	} else {
 		location, context := s.tmpl.ErrorContext(s.node)
 		format = fmt.Sprintf("template: %s: executing %q at <%s>: %s", location, name, doublePercent(context), format)
 	}
 	panic(ExecError{
 		Name: s.tmpl.Name(),
 		Err:  fmt.Errorf(format, args...),
 	})
 }
 
 // writeError is the wrapper type used internally when Execute has an
 // error writing to its output. We strip the wrapper in errRecover.
 // Note that this is not an implementation of error, so it cannot escape
 // from the package as an error value.
 type writeError struct {
 	Err error // Original error.
 }
 
 func (s *state) writeError(err error) {
 	panic(writeError{
 		Err: err,
 	})
 }
 
 // errRecover is the handler that turns panics into returns from the top
 // level of Parse.
 func errRecover(errp *error) {
 	e := recover()
 	if e != nil {
 		switch err := e.(type) {
 		case runtime.Error:
 			panic(e)
 		case writeError:
 			*errp = err.Err // Strip the wrapper.
 		case ExecError:
 			*errp = err // Keep the wrapper.
 		default:
 			panic(e)
 		}
 	}
 }
 
 // ExecuteTemplate applies the template associated with t that has the given name
 // to the specified data object and writes the output to wr.
 // If an error occurs executing the template or writing its output,
 // execution stops, but partial results may already have been written to
 // the output writer.
 // A template may be executed safely in parallel, although if parallel
 // executions share a Writer the output may be interleaved.
 func (t *Template) ExecuteTemplate(wr io.Writer, name string, data any) error {
 	tmpl := t.Lookup(name)
 	if tmpl == nil {
 		return fmt.Errorf("template: no template %q associated with template %q", name, t.name)
 	}
 	return tmpl.Execute(wr, data)
 }
 
 // Execute applies a parsed template to the specified data object,
 // and writes the output to wr.
 // If an error occurs executing the template or writing its output,
 // execution stops, but partial results may already have been written to
 // the output writer.
 // A template may be executed safely in parallel, although if parallel
 // executions share a Writer the output may be interleaved.
 //
 // If data is a reflect.Value, the template applies to the concrete
 // value that the reflect.Value holds, as in fmt.Print.
 func (t *Template) Execute(wr io.Writer, data any) error {
 	return t.execute(wr, data)
 }
 
 func (t *Template) execute(wr io.Writer, data any) (err error) {
 	defer errRecover(&err)
 	value, ok := data.(reflect.Value)
 	if !ok {
 		value = reflect.ValueOf(data)
 	}
 	state := &state{
 		tmpl: t,
 		wr:   wr,
 		vars: []variable{{"$", value}},
 	}
 	if t.Tree == nil || t.Root == nil {
 		state.errorf("%q is an incomplete or empty template", t.Name())
 	}
 	state.walk(value, t.Root)
 	return
 }
 
 // DefinedTemplates returns a string listing the defined templates,
 // prefixed by the string "; defined templates are: ". If there are none,
 // it returns the empty string. For generating an error message here
 // and in html/template.
 func (t *Template) DefinedTemplates() string {
 	if t.common == nil {
 		return ""
 	}
 	var b strings.Builder
 	t.muTmpl.RLock()
 	defer t.muTmpl.RUnlock()
 	for name, tmpl := range t.tmpl {
 		if tmpl.Tree == nil || tmpl.Root == nil {
 			continue
 		}
 		if b.Len() == 0 {
 			b.WriteString("; defined templates are: ")
 		} else {
 			b.WriteString(", ")
 		}
 		fmt.Fprintf(&b, "%q", name)
 	}
 	return b.String()
 }
 
 // Sentinel errors for use with panic to signal early exits from range loops.
 var (
 	walkBreak    = errors.New("break")
 	walkContinue = errors.New("continue")
 )
 
 // Walk functions step through the major pieces of the template structure,
 // generating output as they go.
 func (s *state) walk(dot reflect.Value, node parse.Node) {
 	s.at(node)
 	switch node := node.(type) {
 	case *parse.ActionNode:
 		// Do not pop variables so they persist until next end.
 		// Also, if the action declares variables, don't print the result.
 		val := s.evalPipeline(dot, node.Pipe)
 		if len(node.Pipe.Decl) == 0 {
 			s.printValue(node, val)
 		}
 	case *parse.BreakNode:
 		panic(walkBreak)
 	case *parse.CommentNode:
 	case *parse.ContinueNode:
 		panic(walkContinue)
 	case *parse.IfNode:
 		s.walkIfOrWith(parse.NodeIf, dot, node.Pipe, node.List, node.ElseList)
 	case *parse.ListNode:
 		for _, node := range node.Nodes {
 			s.walk(dot, node)
 		}
 	case *parse.RangeNode:
 		s.walkRange(dot, node)
 	case *parse.TemplateNode:
 		s.walkTemplate(dot, node)
 	case *parse.TextNode:
 		if _, err := s.wr.Write(node.Text); err != nil {
 			s.writeError(err)
 		}
 	case *parse.WithNode:
 		s.walkIfOrWith(parse.NodeWith, dot, node.Pipe, node.List, node.ElseList)
 	default:
 		s.errorf("unknown node: %s", node)
 	}
 }
 
 // walkIfOrWith walks an 'if' or 'with' node. The two control structures
 // are identical in behavior except that 'with' sets dot.
 func (s *state) walkIfOrWith(typ parse.NodeType, dot reflect.Value, pipe *parse.PipeNode, list, elseList *parse.ListNode) {
 	defer s.pop(s.mark())
 	val := s.evalPipeline(dot, pipe)
 	truth, ok := isTrue(indirectInterface(val))
 	if !ok {
 		s.errorf("if/with can't use %v", val)
 	}
 	if truth {
 		if typ == parse.NodeWith {
 			s.walk(val, list)
 		} else {
 			s.walk(dot, list)
 		}
 	} else if elseList != nil {
 		s.walk(dot, elseList)
 	}
 }
 
 // IsTrue reports whether the value is 'true', in the sense of not the zero of its type,
 // and whether the value has a meaningful truth value. This is the definition of
 // truth used by if and other such actions.
 func IsTrue(val any) (truth, ok bool) {
 	return isTrue(reflect.ValueOf(val))
 }
 
 func isTrueOld(val reflect.Value) (truth, ok bool) {
 	if !val.IsValid() {
 		// Something like var x interface{}, never set. It's a form of nil.
 		return false, true
 	}
 	switch val.Kind() {
 	case reflect.Array, reflect.Map, reflect.Slice, reflect.String:
 		truth = val.Len() > 0
 	case reflect.Bool:
 		truth = val.Bool()
 	case reflect.Complex64, reflect.Complex128:
 		truth = val.Complex() != 0
 	case reflect.Chan, reflect.Func, reflect.Pointer, reflect.Interface:
 		truth = !val.IsNil()
 	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
 		truth = val.Int() != 0
 	case reflect.Float32, reflect.Float64:
 		truth = val.Float() != 0
 	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
 		truth = val.Uint() != 0
 	case reflect.Struct:
 		truth = true // Struct values are always true.
 	default:
 		return
 	}
 	return truth, true
 }
 
 func (s *state) walkRange(dot reflect.Value, r *parse.RangeNode) {
 	s.at(r)
 	defer func() {
 		if r := recover(); r != nil && r != walkBreak {
 			panic(r)
 		}
 	}()
 	defer s.pop(s.mark())
 	val, _ := indirect(s.evalPipeline(dot, r.Pipe))
 	// mark top of stack before any variables in the body are pushed.
 	mark := s.mark()
 	oneIteration := func(index, elem reflect.Value) {
 		// Set top var (lexically the second if there are two) to the element.
 		if len(r.Pipe.Decl) > 0 {
 			s.setTopVar(1, elem)
 		}
 		// Set next var (lexically the first if there are two) to the index.
 		if len(r.Pipe.Decl) > 1 {
 			s.setTopVar(2, index)
 		}
 		defer s.pop(mark)
 		defer func() {
 			// Consume panic(walkContinue)
 			if r := recover(); r != nil && r != walkContinue {
 				panic(r)
 			}
 		}()
 		s.walk(elem, r.List)
 	}
 	switch val.Kind() {
 	case reflect.Array, reflect.Slice:
 		if val.Len() == 0 {
 			break
 		}
 		for i := 0; i < val.Len(); i++ {
 			oneIteration(reflect.ValueOf(i), val.Index(i))
 		}
 		return
 	case reflect.Map:
 		if val.Len() == 0 {
 			break
 		}
 		om := fmtsort.Sort(val)
 		for i, key := range om.Key {
 			oneIteration(key, om.Value[i])
 		}
 		return
 	case reflect.Chan:
 		if val.IsNil() {
 			break
 		}
 		if val.Type().ChanDir() == reflect.SendDir {
 			s.errorf("range over send-only channel %v", val)
 			break
 		}
 		i := 0
 		for ; ; i++ {
 			elem, ok := val.Recv()
 			if !ok {
 				break
 			}
 			oneIteration(reflect.ValueOf(i), elem)
 		}
 		if i == 0 {
 			break
 		}
 		return
 	case reflect.Invalid:
 		break // An invalid value is likely a nil map, etc. and acts like an empty map.
 	default:
 		s.errorf("range can't iterate over %v", val)
 	}
 	if r.ElseList != nil {
 		s.walk(dot, r.ElseList)
 	}
 }
 
 func (s *state) walkTemplate(dot reflect.Value, t *parse.TemplateNode) {
 	s.at(t)
 	tmpl := s.tmpl.Lookup(t.Name)
 	if tmpl == nil {
 		s.errorf("template %q not defined", t.Name)
 	}
 	if s.depth == maxExecDepth {
 		s.errorf("exceeded maximum template depth (%v)", maxExecDepth)
 	}
 	// Variables declared by the pipeline persist.
 	dot = s.evalPipeline(dot, t.Pipe)
 	newState := *s
 	newState.depth++
 	newState.tmpl = tmpl
 	// No dynamic scoping: template invocations inherit no variables.
 	newState.vars = []variable{{"$", dot}}
 	newState.walk(dot, tmpl.Root)
 }
 
 // Eval functions evaluate pipelines, commands, and their elements and extract
 // values from the data structure by examining fields, calling methods, and so on.
 // The printing of those values happens only through walk functions.
 
 // evalPipeline returns the value acquired by evaluating a pipeline. If the
 // pipeline has a variable declaration, the variable will be pushed on the
 // stack. Callers should therefore pop the stack after they are finished
 // executing commands depending on the pipeline value.
 func (s *state) evalPipeline(dot reflect.Value, pipe *parse.PipeNode) (value reflect.Value) {
 	if pipe == nil {
 		return
 	}
 	s.at(pipe)
 	value = missingVal
 	for _, cmd := range pipe.Cmds {
 		value = s.evalCommand(dot, cmd, value) // previous value is this one's final arg.
 		// If the object has type interface{}, dig down one level to the thing inside.
 		if value.Kind() == reflect.Interface && value.Type().NumMethod() == 0 {
 			value = reflect.ValueOf(value.Interface()) // lovely!
 		}
 	}
 	for _, variable := range pipe.Decl {
 		if pipe.IsAssign {
 			s.setVar(variable.Ident[0], value)
 		} else {
 			s.push(variable.Ident[0], value)
 		}
 	}
 	return value
 }
 
 func (s *state) notAFunction(args []parse.Node, final reflect.Value) {
 	if len(args) > 1 || final != missingVal {
 		s.errorf("can't give argument to non-function %s", args[0])
 	}
 }
 
 func (s *state) evalCommand(dot reflect.Value, cmd *parse.CommandNode, final reflect.Value) reflect.Value {
 	firstWord := cmd.Args[0]
 	switch n := firstWord.(type) {
 	case *parse.FieldNode:
 		return s.evalFieldNode(dot, n, cmd.Args, final)
 	case *parse.ChainNode:
 		return s.evalChainNode(dot, n, cmd.Args, final)
 	case *parse.IdentifierNode:
 		// Must be a function.
 		return s.evalFunction(dot, n, cmd, cmd.Args, final)
 	case *parse.PipeNode:
 		// Parenthesized pipeline. The arguments are all inside the pipeline; final must be absent.
 		s.notAFunction(cmd.Args, final)
 		return s.evalPipeline(dot, n)
 	case *parse.VariableNode:
 		return s.evalVariableNode(dot, n, cmd.Args, final)
 	}
 	s.at(firstWord)
 	s.notAFunction(cmd.Args, final)
 	switch word := firstWord.(type) {
 	case *parse.BoolNode:
 		return reflect.ValueOf(word.True)
 	case *parse.DotNode:
 		return dot
 	case *parse.NilNode:
 		s.errorf("nil is not a command")
 	case *parse.NumberNode:
 		return s.idealConstant(word)
 	case *parse.StringNode:
 		return reflect.ValueOf(word.Text)
 	}
 	s.errorf("can't evaluate command %q", firstWord)
 	panic("not reached")
 }
 
 // idealConstant is called to return the value of a number in a context where
 // we don't know the type. In that case, the syntax of the number tells us
 // its type, and we use Go rules to resolve. Note there is no such thing as
 // a uint ideal constant in this situation - the value must be of int type.
 func (s *state) idealConstant(constant *parse.NumberNode) reflect.Value {
 	// These are ideal constants but we don't know the type
 	// and we have no context.  (If it was a method argument,
 	// we'd know what we need.) The syntax guides us to some extent.
 	s.at(constant)
 	switch {
 	case constant.IsComplex:
 		return reflect.ValueOf(constant.Complex128) // incontrovertible.
 
 	case constant.IsFloat &&
 		!isHexInt(constant.Text) && !isRuneInt(constant.Text) &&
 		strings.ContainsAny(constant.Text, ".eEpP"):
 		return reflect.ValueOf(constant.Float64)
 
 	case constant.IsInt:
 		n := int(constant.Int64)
 		if int64(n) != constant.Int64 {
 			s.errorf("%s overflows int", constant.Text)
 		}
 		return reflect.ValueOf(n)
 
 	case constant.IsUint:
 		s.errorf("%s overflows int", constant.Text)
 	}
 	return zero
 }
 
 func isRuneInt(s string) bool {
 	return len(s) > 0 && s[0] == '\''
 }
 
 func isHexInt(s string) bool {
 	return len(s) > 2 && s[0] == '0' && (s[1] == 'x' || s[1] == 'X') && !strings.ContainsAny(s, "pP")
 }
 
 func (s *state) evalFieldNode(dot reflect.Value, field *parse.FieldNode, args []parse.Node, final reflect.Value) reflect.Value {
 	s.at(field)
 	return s.evalFieldChain(dot, dot, field, field.Ident, args, final)
 }
 
 func (s *state) evalChainNode(dot reflect.Value, chain *parse.ChainNode, args []parse.Node, final reflect.Value) reflect.Value {
 	s.at(chain)
 	if len(chain.Field) == 0 {
 		s.errorf("internal error: no fields in evalChainNode")
 	}
 	if chain.Node.Type() == parse.NodeNil {
 		s.errorf("indirection through explicit nil in %s", chain)
 	}
 	// (pipe).Field1.Field2 has pipe as .Node, fields as .Field. Eval the pipeline, then the fields.
 	pipe := s.evalArg(dot, nil, chain.Node)
 	return s.evalFieldChain(dot, pipe, chain, chain.Field, args, final)
 }
 
 func (s *state) evalVariableNode(dot reflect.Value, variable *parse.VariableNode, args []parse.Node, final reflect.Value) reflect.Value {
 	// $x.Field has $x as the first ident, Field as the second. Eval the var, then the fields.
 	s.at(variable)
 	value := s.varValue(variable.Ident[0])
 	if len(variable.Ident) == 1 {
 		s.notAFunction(args, final)
 		return value
 	}
 	return s.evalFieldChain(dot, value, variable, variable.Ident[1:], args, final)
 }
 
 // evalFieldChain evaluates .X.Y.Z possibly followed by arguments.
 // dot is the environment in which to evaluate arguments, while
 // receiver is the value being walked along the chain.
 func (s *state) evalFieldChain(dot, receiver reflect.Value, node parse.Node, ident []string, args []parse.Node, final reflect.Value) reflect.Value {
 	n := len(ident)
 	for i := 0; i < n-1; i++ {
 		receiver = s.evalField(dot, ident[i], node, nil, missingVal, receiver)
 	}
 	// Now if it's a method, it gets the arguments.
 	return s.evalField(dot, ident[n-1], node, args, final, receiver)
 }
 
 func (s *state) evalFunctionOld(dot reflect.Value, node *parse.IdentifierNode, cmd parse.Node, args []parse.Node, final reflect.Value) reflect.Value {
 	s.at(node)
 	name := node.Ident
 	function, isBuiltin, ok := findFunction(name, s.tmpl)
 	if !ok {
 		s.errorf("%q is not a defined function", name)
 	}
 	return s.evalCall(dot, function, isBuiltin, cmd, name, args, final)
 }
 
 // evalField evaluates an expression like (.Field) or (.Field arg1 arg2).
 // The 'final' argument represents the return value from the preceding
 // value of the pipeline, if any.
 func (s *state) evalFieldOld(dot reflect.Value, fieldName string, node parse.Node, args []parse.Node, final, receiver reflect.Value) reflect.Value {
 	if !receiver.IsValid() {
 		if s.tmpl.option.missingKey == mapError { // Treat invalid value as missing map key.
 			s.errorf("nil data; no entry for key %q", fieldName)
 		}
 		return zero
 	}
 	typ := receiver.Type()
 	receiver, isNil := indirect(receiver)
 	if receiver.Kind() == reflect.Interface && isNil {
 		// Calling a method on a nil interface can't work. The
 		// MethodByName method call below would panic.
 		s.errorf("nil pointer evaluating %s.%s", typ, fieldName)
 		return zero
 	}
 
 	// Unless it's an interface, need to get to a value of type *T to guarantee
 	// we see all methods of T and *T.
 	ptr := receiver
 	if ptr.Kind() != reflect.Interface && ptr.Kind() != reflect.Pointer && ptr.CanAddr() {
 		ptr = ptr.Addr()
 	}
 	if method := ptr.MethodByName(fieldName); method.IsValid() {
 		return s.evalCall(dot, method, false, node, fieldName, args, final)
 	}
 	hasArgs := len(args) > 1 || final != missingVal
 	// It's not a method; must be a field of a struct or an element of a map.
 	switch receiver.Kind() {
 	case reflect.Struct:
 		tField, ok := receiver.Type().FieldByName(fieldName)
 		if ok {
 			field, err := receiver.FieldByIndexErr(tField.Index)
 			if !tField.IsExported() {
 				s.errorf("%s is an unexported field of struct type %s", fieldName, typ)
 			}
 			if err != nil {
 				s.errorf("%v", err)
 			}
 			// If it's a function, we must call it.
 			if hasArgs {
 				s.errorf("%s has arguments but cannot be invoked as function", fieldName)
 			}
 			return field
 		}
 	case reflect.Map:
 		// If it's a map, attempt to use the field name as a key.
 		nameVal := reflect.ValueOf(fieldName)
 		if nameVal.Type().AssignableTo(receiver.Type().Key()) {
 			if hasArgs {
 				s.errorf("%s is not a method but has arguments", fieldName)
 			}
 			result := receiver.MapIndex(nameVal)
 			if !result.IsValid() {
 				switch s.tmpl.option.missingKey {
 				case mapInvalid:
 					// Just use the invalid value.
 				case mapZeroValue:
 					result = reflect.Zero(receiver.Type().Elem())
 				case mapError:
 					s.errorf("map has no entry for key %q", fieldName)
 				}
 			}
 			return result
 		}
 	case reflect.Pointer:
 		etyp := receiver.Type().Elem()
 		if etyp.Kind() == reflect.Struct {
 			if _, ok := etyp.FieldByName(fieldName); !ok {
 				// If there's no such field, say "can't evaluate"
 				// instead of "nil pointer evaluating".
 				break
 			}
 		}
 		if isNil {
 			s.errorf("nil pointer evaluating %s.%s", typ, fieldName)
 		}
 	}
 	s.errorf("can't evaluate field %s in type %s", fieldName, typ)
 	panic("not reached")
 }
 
 var (
 	errorType        = reflect.TypeOf((*error)(nil)).Elem()
 	fmtStringerType  = reflect.TypeOf((*fmt.Stringer)(nil)).Elem()
 	reflectValueType = reflect.TypeOf((*reflect.Value)(nil)).Elem()
 )
 
 // evalCall executes a function or method call. If it's a method, fun already has the receiver bound, so
 // it looks just like a function call. The arg list, if non-nil, includes (in the manner of the shell), arg[0]
 // as the function itself.
 func (s *state) evalCallOld(dot, fun reflect.Value, isBuiltin bool, node parse.Node, name string, args []parse.Node, final reflect.Value) reflect.Value {
 	if args != nil {
 		args = args[1:] // Zeroth arg is function name/node; not passed to function.
 	}
 	typ := fun.Type()
 	numIn := len(args)
 	if final != missingVal {
 		numIn++
 	}
 	numFixed := len(args)
 	if typ.IsVariadic() {
 		numFixed = typ.NumIn() - 1 // last arg is the variadic one.
 		if numIn < numFixed {
 			s.errorf("wrong number of args for %s: want at least %d got %d", name, typ.NumIn()-1, len(args))
 		}
 	} else if numIn != typ.NumIn() {
 		s.errorf("wrong number of args for %s: want %d got %d", name, typ.NumIn(), numIn)
 	}
 	if !goodFunc(typ) {
 		// TODO: This could still be a confusing error; maybe goodFunc should provide info.
 		s.errorf("can't call method/function %q with %d results", name, typ.NumOut())
 	}
 
 	unwrap := func(v reflect.Value) reflect.Value {
 		if v.Type() == reflectValueType {
 			v = v.Interface().(reflect.Value)
 		}
 		return v
 	}
 
 	// Special case for builtin and/or, which short-circuit.
 	if isBuiltin && (name == "and" || name == "or") {
 		argType := typ.In(0)
 		var v reflect.Value
 		for _, arg := range args {
 			v = s.evalArg(dot, argType, arg).Interface().(reflect.Value)
 			if truth(v) == (name == "or") {
 				// This value was already unwrapped
 				// by the .Interface().(reflect.Value).
 				return v
 			}
 		}
 		if final != missingVal {
 			// The last argument to and/or is coming from
 			// the pipeline. We didn't short circuit on an earlier
 			// argument, so we are going to return this one.
 			// We don't have to evaluate final, but we do
 			// have to check its type. Then, since we are
 			// going to return it, we have to unwrap it.
 			v = unwrap(s.validateType(final, argType))
 		}
 		return v
 	}
 
 	// Build the arg list.
 	argv := make([]reflect.Value, numIn)
 	// Args must be evaluated. Fixed args first.
 	i := 0
 	for ; i < numFixed && i < len(args); i++ {
 		argv[i] = s.evalArg(dot, typ.In(i), args[i])
 	}
 	// Now the ... args.
 	if typ.IsVariadic() {
 		argType := typ.In(typ.NumIn() - 1).Elem() // Argument is a slice.
 		for ; i < len(args); i++ {
 			argv[i] = s.evalArg(dot, argType, args[i])
 		}
 	}
 	// Add final value if necessary.
 	if final != missingVal {
 		t := typ.In(typ.NumIn() - 1)
 		if typ.IsVariadic() {
 			if numIn-1 < numFixed {
 				// The added final argument corresponds to a fixed parameter of the function.
 				// Validate against the type of the actual parameter.
 				t = typ.In(numIn - 1)
 			} else {
 				// The added final argument corresponds to the variadic part.
 				// Validate against the type of the elements of the variadic slice.
 				t = t.Elem()
 			}
 		}
 		argv[i] = s.validateType(final, t)
 	}
 	v, err := safeCall(fun, argv)
 	// If we have an error that is not nil, stop execution and return that
 	// error to the caller.
 	if err != nil {
 		s.at(node)
 		s.errorf("error calling %s: %w", name, err)
 	}
 	return unwrap(v)
 }
 
 // canBeNil reports whether an untyped nil can be assigned to the type. See reflect.Zero.
 func canBeNil(typ reflect.Type) bool {
 	switch typ.Kind() {
 	case reflect.Chan, reflect.Func, reflect.Interface, reflect.Map, reflect.Pointer, reflect.Slice:
 		return true
 	case reflect.Struct:
 		return typ == reflectValueType
 	}
 	return false
 }
 
 // validateType guarantees that the value is valid and assignable to the type.
 func (s *state) validateType(value reflect.Value, typ reflect.Type) reflect.Value {
 	if !value.IsValid() {
 		if typ == nil {
 			// An untyped nil interface{}. Accept as a proper nil value.
 			return reflect.ValueOf(nil)
 		}
 		if canBeNil(typ) {
 			// Like above, but use the zero value of the non-nil type.
 			return reflect.Zero(typ)
 		}
 		s.errorf("invalid value; expected %s", typ)
 	}
 	if typ == reflectValueType && value.Type() != typ {
 		return reflect.ValueOf(value)
 	}
 	if typ != nil && !value.Type().AssignableTo(typ) {
 		if value.Kind() == reflect.Interface && !value.IsNil() {
 			value = value.Elem()
 			if value.Type().AssignableTo(typ) {
 				return value
 			}
 			// fallthrough
 		}
 		// Does one dereference or indirection work? We could do more, as we
 		// do with method receivers, but that gets messy and method receivers
 		// are much more constrained, so it makes more sense there than here.
 		// Besides, one is almost always all you need.
 		switch {
 		case value.Kind() == reflect.Pointer && value.Type().Elem().AssignableTo(typ):
 			value = value.Elem()
 			if !value.IsValid() {
 				s.errorf("dereference of nil pointer of type %s", typ)
 			}
 		case reflect.PointerTo(value.Type()).AssignableTo(typ) && value.CanAddr():
 			value = value.Addr()
 		default:
 			s.errorf("wrong type for value; expected %s; got %s", typ, value.Type())
 		}
 	}
 	return value
 }
 
 func (s *state) evalArg(dot reflect.Value, typ reflect.Type, n parse.Node) reflect.Value {
 	s.at(n)
 	switch arg := n.(type) {
 	case *parse.DotNode:
 		return s.validateType(dot, typ)
 	case *parse.NilNode:
 		if canBeNil(typ) {
 			return reflect.Zero(typ)
 		}
 		s.errorf("cannot assign nil to %s", typ)
 	case *parse.FieldNode:
 		return s.validateType(s.evalFieldNode(dot, arg, []parse.Node{n}, missingVal), typ)
 	case *parse.VariableNode:
 		return s.validateType(s.evalVariableNode(dot, arg, nil, missingVal), typ)
 	case *parse.PipeNode:
 		return s.validateType(s.evalPipeline(dot, arg), typ)
 	case *parse.IdentifierNode:
 		return s.validateType(s.evalFunction(dot, arg, arg, nil, missingVal), typ)
 	case *parse.ChainNode:
 		return s.validateType(s.evalChainNode(dot, arg, nil, missingVal), typ)
 	}
 	switch typ.Kind() {
 	case reflect.Bool:
 		return s.evalBool(typ, n)
 	case reflect.Complex64, reflect.Complex128:
 		return s.evalComplex(typ, n)
 	case reflect.Float32, reflect.Float64:
 		return s.evalFloat(typ, n)
 	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
 		return s.evalInteger(typ, n)
 	case reflect.Interface:
 		if typ.NumMethod() == 0 {
 			return s.evalEmptyInterface(dot, n)
 		}
 	case reflect.Struct:
 		if typ == reflectValueType {
 			return reflect.ValueOf(s.evalEmptyInterface(dot, n))
 		}
 	case reflect.String:
 		return s.evalString(typ, n)
 	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
 		return s.evalUnsignedInteger(typ, n)
 	}
 	s.errorf("can't handle %s for arg of type %s", n, typ)
 	panic("not reached")
 }
 
 func (s *state) evalBool(typ reflect.Type, n parse.Node) reflect.Value {
 	s.at(n)
 	if n, ok := n.(*parse.BoolNode); ok {
 		value := reflect.New(typ).Elem()
 		value.SetBool(n.True)
 		return value
 	}
 	s.errorf("expected bool; found %s", n)
 	panic("not reached")
 }
 
 func (s *state) evalString(typ reflect.Type, n parse.Node) reflect.Value {
 	s.at(n)
 	if n, ok := n.(*parse.StringNode); ok {
 		value := reflect.New(typ).Elem()
 		value.SetString(n.Text)
 		return value
 	}
 	s.errorf("expected string; found %s", n)
 	panic("not reached")
 }
 
 func (s *state) evalInteger(typ reflect.Type, n parse.Node) reflect.Value {
 	s.at(n)
 	if n, ok := n.(*parse.NumberNode); ok && n.IsInt {
 		value := reflect.New(typ).Elem()
 		value.SetInt(n.Int64)
 		return value
 	}
 	s.errorf("expected integer; found %s", n)
 	panic("not reached")
 }
 
 func (s *state) evalUnsignedInteger(typ reflect.Type, n parse.Node) reflect.Value {
 	s.at(n)
 	if n, ok := n.(*parse.NumberNode); ok && n.IsUint {
 		value := reflect.New(typ).Elem()
 		value.SetUint(n.Uint64)
 		return value
 	}
 	s.errorf("expected unsigned integer; found %s", n)
 	panic("not reached")
 }
 
 func (s *state) evalFloat(typ reflect.Type, n parse.Node) reflect.Value {
 	s.at(n)
 	if n, ok := n.(*parse.NumberNode); ok && n.IsFloat {
 		value := reflect.New(typ).Elem()
 		value.SetFloat(n.Float64)
 		return value
 	}
 	s.errorf("expected float; found %s", n)
 	panic("not reached")
 }
 
 func (s *state) evalComplex(typ reflect.Type, n parse.Node) reflect.Value {
 	if n, ok := n.(*parse.NumberNode); ok && n.IsComplex {
 		value := reflect.New(typ).Elem()
 		value.SetComplex(n.Complex128)
 		return value
 	}
 	s.errorf("expected complex; found %s", n)
 	panic("not reached")
 }
 
 func (s *state) evalEmptyInterface(dot reflect.Value, n parse.Node) reflect.Value {
 	s.at(n)
 	switch n := n.(type) {
 	case *parse.BoolNode:
 		return reflect.ValueOf(n.True)
 	case *parse.DotNode:
 		return dot
 	case *parse.FieldNode:
 		return s.evalFieldNode(dot, n, nil, missingVal)
 	case *parse.IdentifierNode:
 		return s.evalFunction(dot, n, n, nil, missingVal)
 	case *parse.NilNode:
 		// NilNode is handled in evalArg, the only place that calls here.
 		s.errorf("evalEmptyInterface: nil (can't happen)")
 	case *parse.NumberNode:
 		return s.idealConstant(n)
 	case *parse.StringNode:
 		return reflect.ValueOf(n.Text)
 	case *parse.VariableNode:
 		return s.evalVariableNode(dot, n, nil, missingVal)
 	case *parse.PipeNode:
 		return s.evalPipeline(dot, n)
 	}
 	s.errorf("can't handle assignment of %s to empty interface argument", n)
 	panic("not reached")
 }
 
 // indirect returns the item at the end of indirection, and a bool to indicate
 // if it's nil. If the returned bool is true, the returned value's kind will be
 // either a pointer or interface.
 func indirect(v reflect.Value) (rv reflect.Value, isNil bool) {
 	for ; v.Kind() == reflect.Pointer || v.Kind() == reflect.Interface; v = v.Elem() {
 		if v.IsNil() {
 			return v, true
 		}
 	}
 	return v, false
 }
 
 // indirectInterface returns the concrete value in an interface value,
 // or else the zero reflect.Value.
 // That is, if v represents the interface value x, the result is the same as reflect.ValueOf(x):
 // the fact that x was an interface value is forgotten.
 func indirectInterface(v reflect.Value) reflect.Value {
 	if v.Kind() != reflect.Interface {
 		return v
 	}
 	if v.IsNil() {
 		return reflect.Value{}
 	}
 	return v.Elem()
 }
 
 // printValue writes the textual representation of the value to the output of
 // the template.
 func (s *state) printValue(n parse.Node, v reflect.Value) {
 	s.at(n)
 	iface, ok := printableValue(v)
 	if !ok {
 		s.errorf("can't print %s of type %s", n, v.Type())
 	}
 	_, err := fmt.Fprint(s.wr, iface)
 	if err != nil {
 		s.writeError(err)
 	}
 }
 
 // printableValue returns the, possibly indirected, interface value inside v that
 // is best for a call to formatted printer.
 func printableValue(v reflect.Value) (any, bool) {
 	if v.Kind() == reflect.Pointer {
 		v, _ = indirect(v) // fmt.Fprint handles nil.
 	}
 	if !v.IsValid() {
 		return "<no value>", true
 	}
 
 	if !v.Type().Implements(errorType) && !v.Type().Implements(fmtStringerType) {
 		if v.CanAddr() && (reflect.PointerTo(v.Type()).Implements(errorType) || reflect.PointerTo(v.Type()).Implements(fmtStringerType)) {
 			v = v.Addr()
 		} else {
 			switch v.Kind() {
 			case reflect.Chan, reflect.Func:
 				return nil, false
 			}
 		}
 	}
 	return v.Interface(), true
 }