Run Format

Source file src/pkg/text/template/exec.go

     1	// Copyright 2011 The Go Authors. All rights reserved.
     2	// Use of this source code is governed by a BSD-style
     3	// license that can be found in the LICENSE file.
     4	
     5	package template
     6	
     7	import (
     8		"bytes"
     9		"fmt"
    10		"io"
    11		"reflect"
    12		"runtime"
    13		"sort"
    14		"strings"
    15		"text/template/parse"
    16	)
    17	
    18	// state represents the state of an execution. It's not part of the
    19	// template so that multiple executions of the same template
    20	// can execute in parallel.
    21	type state struct {
    22		tmpl *Template
    23		wr   io.Writer
    24		node parse.Node // current node, for errors
    25		vars []variable // push-down stack of variable values.
    26	}
    27	
    28	// variable holds the dynamic value of a variable such as $, $x etc.
    29	type variable struct {
    30		name  string
    31		value reflect.Value
    32	}
    33	
    34	// push pushes a new variable on the stack.
    35	func (s *state) push(name string, value reflect.Value) {
    36		s.vars = append(s.vars, variable{name, value})
    37	}
    38	
    39	// mark returns the length of the variable stack.
    40	func (s *state) mark() int {
    41		return len(s.vars)
    42	}
    43	
    44	// pop pops the variable stack up to the mark.
    45	func (s *state) pop(mark int) {
    46		s.vars = s.vars[0:mark]
    47	}
    48	
    49	// setVar overwrites the top-nth variable on the stack. Used by range iterations.
    50	func (s *state) setVar(n int, value reflect.Value) {
    51		s.vars[len(s.vars)-n].value = value
    52	}
    53	
    54	// varValue returns the value of the named variable.
    55	func (s *state) varValue(name string) reflect.Value {
    56		for i := s.mark() - 1; i >= 0; i-- {
    57			if s.vars[i].name == name {
    58				return s.vars[i].value
    59			}
    60		}
    61		s.errorf("undefined variable: %s", name)
    62		return zero
    63	}
    64	
    65	var zero reflect.Value
    66	
    67	// at marks the state to be on node n, for error reporting.
    68	func (s *state) at(node parse.Node) {
    69		s.node = node
    70	}
    71	
    72	// doublePercent returns the string with %'s replaced by %%, if necessary,
    73	// so it can be used safely inside a Printf format string.
    74	func doublePercent(str string) string {
    75		if strings.Contains(str, "%") {
    76			str = strings.Replace(str, "%", "%%", -1)
    77		}
    78		return str
    79	}
    80	
    81	// errorf formats the error and terminates processing.
    82	func (s *state) errorf(format string, args ...interface{}) {
    83		name := doublePercent(s.tmpl.Name())
    84		if s.node == nil {
    85			format = fmt.Sprintf("template: %s: %s", name, format)
    86		} else {
    87			location, context := s.tmpl.ErrorContext(s.node)
    88			format = fmt.Sprintf("template: %s: executing %q at <%s>: %s", location, name, doublePercent(context), format)
    89		}
    90		panic(fmt.Errorf(format, args...))
    91	}
    92	
    93	// errRecover is the handler that turns panics into returns from the top
    94	// level of Parse.
    95	func errRecover(errp *error) {
    96		e := recover()
    97		if e != nil {
    98			switch err := e.(type) {
    99			case runtime.Error:
   100				panic(e)
   101			case error:
   102				*errp = err
   103			default:
   104				panic(e)
   105			}
   106		}
   107	}
   108	
   109	// ExecuteTemplate applies the template associated with t that has the given name
   110	// to the specified data object and writes the output to wr.
   111	func (t *Template) ExecuteTemplate(wr io.Writer, name string, data interface{}) error {
   112		tmpl := t.tmpl[name]
   113		if tmpl == nil {
   114			return fmt.Errorf("template: no template %q associated with template %q", name, t.name)
   115		}
   116		return tmpl.Execute(wr, data)
   117	}
   118	
   119	// Execute applies a parsed template to the specified data object,
   120	// and writes the output to wr.
   121	func (t *Template) Execute(wr io.Writer, data interface{}) (err error) {
   122		defer errRecover(&err)
   123		value := reflect.ValueOf(data)
   124		state := &state{
   125			tmpl: t,
   126			wr:   wr,
   127			vars: []variable{{"$", value}},
   128		}
   129		t.init()
   130		if t.Tree == nil || t.Root == nil {
   131			var b bytes.Buffer
   132			for name, tmpl := range t.tmpl {
   133				if tmpl.Tree == nil || tmpl.Root == nil {
   134					continue
   135				}
   136				if b.Len() > 0 {
   137					b.WriteString(", ")
   138				}
   139				fmt.Fprintf(&b, "%q", name)
   140			}
   141			var s string
   142			if b.Len() > 0 {
   143				s = "; defined templates are: " + b.String()
   144			}
   145			state.errorf("%q is an incomplete or empty template%s", t.Name(), s)
   146		}
   147		state.walk(value, t.Root)
   148		return
   149	}
   150	
   151	// Walk functions step through the major pieces of the template structure,
   152	// generating output as they go.
   153	func (s *state) walk(dot reflect.Value, node parse.Node) {
   154		s.at(node)
   155		switch node := node.(type) {
   156		case *parse.ActionNode:
   157			// Do not pop variables so they persist until next end.
   158			// Also, if the action declares variables, don't print the result.
   159			val := s.evalPipeline(dot, node.Pipe)
   160			if len(node.Pipe.Decl) == 0 {
   161				s.printValue(node, val)
   162			}
   163		case *parse.IfNode:
   164			s.walkIfOrWith(parse.NodeIf, dot, node.Pipe, node.List, node.ElseList)
   165		case *parse.ListNode:
   166			for _, node := range node.Nodes {
   167				s.walk(dot, node)
   168			}
   169		case *parse.RangeNode:
   170			s.walkRange(dot, node)
   171		case *parse.TemplateNode:
   172			s.walkTemplate(dot, node)
   173		case *parse.TextNode:
   174			if _, err := s.wr.Write(node.Text); err != nil {
   175				s.errorf("%s", err)
   176			}
   177		case *parse.WithNode:
   178			s.walkIfOrWith(parse.NodeWith, dot, node.Pipe, node.List, node.ElseList)
   179		default:
   180			s.errorf("unknown node: %s", node)
   181		}
   182	}
   183	
   184	// walkIfOrWith walks an 'if' or 'with' node. The two control structures
   185	// are identical in behavior except that 'with' sets dot.
   186	func (s *state) walkIfOrWith(typ parse.NodeType, dot reflect.Value, pipe *parse.PipeNode, list, elseList *parse.ListNode) {
   187		defer s.pop(s.mark())
   188		val := s.evalPipeline(dot, pipe)
   189		truth, ok := isTrue(val)
   190		if !ok {
   191			s.errorf("if/with can't use %v", val)
   192		}
   193		if truth {
   194			if typ == parse.NodeWith {
   195				s.walk(val, list)
   196			} else {
   197				s.walk(dot, list)
   198			}
   199		} else if elseList != nil {
   200			s.walk(dot, elseList)
   201		}
   202	}
   203	
   204	// isTrue reports whether the value is 'true', in the sense of not the zero of its type,
   205	// and whether the value has a meaningful truth value.
   206	func isTrue(val reflect.Value) (truth, ok bool) {
   207		if !val.IsValid() {
   208			// Something like var x interface{}, never set. It's a form of nil.
   209			return false, true
   210		}
   211		switch val.Kind() {
   212		case reflect.Array, reflect.Map, reflect.Slice, reflect.String:
   213			truth = val.Len() > 0
   214		case reflect.Bool:
   215			truth = val.Bool()
   216		case reflect.Complex64, reflect.Complex128:
   217			truth = val.Complex() != 0
   218		case reflect.Chan, reflect.Func, reflect.Ptr, reflect.Interface:
   219			truth = !val.IsNil()
   220		case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
   221			truth = val.Int() != 0
   222		case reflect.Float32, reflect.Float64:
   223			truth = val.Float() != 0
   224		case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
   225			truth = val.Uint() != 0
   226		case reflect.Struct:
   227			truth = true // Struct values are always true.
   228		default:
   229			return
   230		}
   231		return truth, true
   232	}
   233	
   234	func (s *state) walkRange(dot reflect.Value, r *parse.RangeNode) {
   235		s.at(r)
   236		defer s.pop(s.mark())
   237		val, _ := indirect(s.evalPipeline(dot, r.Pipe))
   238		// mark top of stack before any variables in the body are pushed.
   239		mark := s.mark()
   240		oneIteration := func(index, elem reflect.Value) {
   241			// Set top var (lexically the second if there are two) to the element.
   242			if len(r.Pipe.Decl) > 0 {
   243				s.setVar(1, elem)
   244			}
   245			// Set next var (lexically the first if there are two) to the index.
   246			if len(r.Pipe.Decl) > 1 {
   247				s.setVar(2, index)
   248			}
   249			s.walk(elem, r.List)
   250			s.pop(mark)
   251		}
   252		switch val.Kind() {
   253		case reflect.Array, reflect.Slice:
   254			if val.Len() == 0 {
   255				break
   256			}
   257			for i := 0; i < val.Len(); i++ {
   258				oneIteration(reflect.ValueOf(i), val.Index(i))
   259			}
   260			return
   261		case reflect.Map:
   262			if val.Len() == 0 {
   263				break
   264			}
   265			for _, key := range sortKeys(val.MapKeys()) {
   266				oneIteration(key, val.MapIndex(key))
   267			}
   268			return
   269		case reflect.Chan:
   270			if val.IsNil() {
   271				break
   272			}
   273			i := 0
   274			for ; ; i++ {
   275				elem, ok := val.Recv()
   276				if !ok {
   277					break
   278				}
   279				oneIteration(reflect.ValueOf(i), elem)
   280			}
   281			if i == 0 {
   282				break
   283			}
   284			return
   285		case reflect.Invalid:
   286			break // An invalid value is likely a nil map, etc. and acts like an empty map.
   287		default:
   288			s.errorf("range can't iterate over %v", val)
   289		}
   290		if r.ElseList != nil {
   291			s.walk(dot, r.ElseList)
   292		}
   293	}
   294	
   295	func (s *state) walkTemplate(dot reflect.Value, t *parse.TemplateNode) {
   296		s.at(t)
   297		tmpl := s.tmpl.tmpl[t.Name]
   298		if tmpl == nil {
   299			s.errorf("template %q not defined", t.Name)
   300		}
   301		// Variables declared by the pipeline persist.
   302		dot = s.evalPipeline(dot, t.Pipe)
   303		newState := *s
   304		newState.tmpl = tmpl
   305		// No dynamic scoping: template invocations inherit no variables.
   306		newState.vars = []variable{{"$", dot}}
   307		newState.walk(dot, tmpl.Root)
   308	}
   309	
   310	// Eval functions evaluate pipelines, commands, and their elements and extract
   311	// values from the data structure by examining fields, calling methods, and so on.
   312	// The printing of those values happens only through walk functions.
   313	
   314	// evalPipeline returns the value acquired by evaluating a pipeline. If the
   315	// pipeline has a variable declaration, the variable will be pushed on the
   316	// stack. Callers should therefore pop the stack after they are finished
   317	// executing commands depending on the pipeline value.
   318	func (s *state) evalPipeline(dot reflect.Value, pipe *parse.PipeNode) (value reflect.Value) {
   319		if pipe == nil {
   320			return
   321		}
   322		s.at(pipe)
   323		for _, cmd := range pipe.Cmds {
   324			value = s.evalCommand(dot, cmd, value) // previous value is this one's final arg.
   325			// If the object has type interface{}, dig down one level to the thing inside.
   326			if value.Kind() == reflect.Interface && value.Type().NumMethod() == 0 {
   327				value = reflect.ValueOf(value.Interface()) // lovely!
   328			}
   329		}
   330		for _, variable := range pipe.Decl {
   331			s.push(variable.Ident[0], value)
   332		}
   333		return value
   334	}
   335	
   336	func (s *state) notAFunction(args []parse.Node, final reflect.Value) {
   337		if len(args) > 1 || final.IsValid() {
   338			s.errorf("can't give argument to non-function %s", args[0])
   339		}
   340	}
   341	
   342	func (s *state) evalCommand(dot reflect.Value, cmd *parse.CommandNode, final reflect.Value) reflect.Value {
   343		firstWord := cmd.Args[0]
   344		switch n := firstWord.(type) {
   345		case *parse.FieldNode:
   346			return s.evalFieldNode(dot, n, cmd.Args, final)
   347		case *parse.ChainNode:
   348			return s.evalChainNode(dot, n, cmd.Args, final)
   349		case *parse.IdentifierNode:
   350			// Must be a function.
   351			return s.evalFunction(dot, n, cmd, cmd.Args, final)
   352		case *parse.PipeNode:
   353			// Parenthesized pipeline. The arguments are all inside the pipeline; final is ignored.
   354			return s.evalPipeline(dot, n)
   355		case *parse.VariableNode:
   356			return s.evalVariableNode(dot, n, cmd.Args, final)
   357		}
   358		s.at(firstWord)
   359		s.notAFunction(cmd.Args, final)
   360		switch word := firstWord.(type) {
   361		case *parse.BoolNode:
   362			return reflect.ValueOf(word.True)
   363		case *parse.DotNode:
   364			return dot
   365		case *parse.NilNode:
   366			s.errorf("nil is not a command")
   367		case *parse.NumberNode:
   368			return s.idealConstant(word)
   369		case *parse.StringNode:
   370			return reflect.ValueOf(word.Text)
   371		}
   372		s.errorf("can't evaluate command %q", firstWord)
   373		panic("not reached")
   374	}
   375	
   376	// idealConstant is called to return the value of a number in a context where
   377	// we don't know the type. In that case, the syntax of the number tells us
   378	// its type, and we use Go rules to resolve.  Note there is no such thing as
   379	// a uint ideal constant in this situation - the value must be of int type.
   380	func (s *state) idealConstant(constant *parse.NumberNode) reflect.Value {
   381		// These are ideal constants but we don't know the type
   382		// and we have no context.  (If it was a method argument,
   383		// we'd know what we need.) The syntax guides us to some extent.
   384		s.at(constant)
   385		switch {
   386		case constant.IsComplex:
   387			return reflect.ValueOf(constant.Complex128) // incontrovertible.
   388		case constant.IsFloat && strings.IndexAny(constant.Text, ".eE") >= 0:
   389			return reflect.ValueOf(constant.Float64)
   390		case constant.IsInt:
   391			n := int(constant.Int64)
   392			if int64(n) != constant.Int64 {
   393				s.errorf("%s overflows int", constant.Text)
   394			}
   395			return reflect.ValueOf(n)
   396		case constant.IsUint:
   397			s.errorf("%s overflows int", constant.Text)
   398		}
   399		return zero
   400	}
   401	
   402	func (s *state) evalFieldNode(dot reflect.Value, field *parse.FieldNode, args []parse.Node, final reflect.Value) reflect.Value {
   403		s.at(field)
   404		return s.evalFieldChain(dot, dot, field, field.Ident, args, final)
   405	}
   406	
   407	func (s *state) evalChainNode(dot reflect.Value, chain *parse.ChainNode, args []parse.Node, final reflect.Value) reflect.Value {
   408		s.at(chain)
   409		// (pipe).Field1.Field2 has pipe as .Node, fields as .Field. Eval the pipeline, then the fields.
   410		pipe := s.evalArg(dot, nil, chain.Node)
   411		if len(chain.Field) == 0 {
   412			s.errorf("internal error: no fields in evalChainNode")
   413		}
   414		return s.evalFieldChain(dot, pipe, chain, chain.Field, args, final)
   415	}
   416	
   417	func (s *state) evalVariableNode(dot reflect.Value, variable *parse.VariableNode, args []parse.Node, final reflect.Value) reflect.Value {
   418		// $x.Field has $x as the first ident, Field as the second. Eval the var, then the fields.
   419		s.at(variable)
   420		value := s.varValue(variable.Ident[0])
   421		if len(variable.Ident) == 1 {
   422			s.notAFunction(args, final)
   423			return value
   424		}
   425		return s.evalFieldChain(dot, value, variable, variable.Ident[1:], args, final)
   426	}
   427	
   428	// evalFieldChain evaluates .X.Y.Z possibly followed by arguments.
   429	// dot is the environment in which to evaluate arguments, while
   430	// receiver is the value being walked along the chain.
   431	func (s *state) evalFieldChain(dot, receiver reflect.Value, node parse.Node, ident []string, args []parse.Node, final reflect.Value) reflect.Value {
   432		n := len(ident)
   433		for i := 0; i < n-1; i++ {
   434			receiver = s.evalField(dot, ident[i], node, nil, zero, receiver)
   435		}
   436		// Now if it's a method, it gets the arguments.
   437		return s.evalField(dot, ident[n-1], node, args, final, receiver)
   438	}
   439	
   440	func (s *state) evalFunction(dot reflect.Value, node *parse.IdentifierNode, cmd parse.Node, args []parse.Node, final reflect.Value) reflect.Value {
   441		s.at(node)
   442		name := node.Ident
   443		function, ok := findFunction(name, s.tmpl)
   444		if !ok {
   445			s.errorf("%q is not a defined function", name)
   446		}
   447		return s.evalCall(dot, function, cmd, name, args, final)
   448	}
   449	
   450	// evalField evaluates an expression like (.Field) or (.Field arg1 arg2).
   451	// The 'final' argument represents the return value from the preceding
   452	// value of the pipeline, if any.
   453	func (s *state) evalField(dot reflect.Value, fieldName string, node parse.Node, args []parse.Node, final, receiver reflect.Value) reflect.Value {
   454		if !receiver.IsValid() {
   455			return zero
   456		}
   457		typ := receiver.Type()
   458		receiver, _ = indirect(receiver)
   459		// Unless it's an interface, need to get to a value of type *T to guarantee
   460		// we see all methods of T and *T.
   461		ptr := receiver
   462		if ptr.Kind() != reflect.Interface && ptr.CanAddr() {
   463			ptr = ptr.Addr()
   464		}
   465		if method := ptr.MethodByName(fieldName); method.IsValid() {
   466			return s.evalCall(dot, method, node, fieldName, args, final)
   467		}
   468		hasArgs := len(args) > 1 || final.IsValid()
   469		// It's not a method; must be a field of a struct or an element of a map. The receiver must not be nil.
   470		receiver, isNil := indirect(receiver)
   471		if isNil {
   472			s.errorf("nil pointer evaluating %s.%s", typ, fieldName)
   473		}
   474		switch receiver.Kind() {
   475		case reflect.Struct:
   476			tField, ok := receiver.Type().FieldByName(fieldName)
   477			if ok {
   478				field := receiver.FieldByIndex(tField.Index)
   479				if tField.PkgPath != "" { // field is unexported
   480					s.errorf("%s is an unexported field of struct type %s", fieldName, typ)
   481				}
   482				// If it's a function, we must call it.
   483				if hasArgs {
   484					s.errorf("%s has arguments but cannot be invoked as function", fieldName)
   485				}
   486				return field
   487			}
   488			s.errorf("%s is not a field of struct type %s", fieldName, typ)
   489		case reflect.Map:
   490			// If it's a map, attempt to use the field name as a key.
   491			nameVal := reflect.ValueOf(fieldName)
   492			if nameVal.Type().AssignableTo(receiver.Type().Key()) {
   493				if hasArgs {
   494					s.errorf("%s is not a method but has arguments", fieldName)
   495				}
   496				return receiver.MapIndex(nameVal)
   497			}
   498		}
   499		s.errorf("can't evaluate field %s in type %s", fieldName, typ)
   500		panic("not reached")
   501	}
   502	
   503	var (
   504		errorType       = reflect.TypeOf((*error)(nil)).Elem()
   505		fmtStringerType = reflect.TypeOf((*fmt.Stringer)(nil)).Elem()
   506	)
   507	
   508	// evalCall executes a function or method call. If it's a method, fun already has the receiver bound, so
   509	// it looks just like a function call.  The arg list, if non-nil, includes (in the manner of the shell), arg[0]
   510	// as the function itself.
   511	func (s *state) evalCall(dot, fun reflect.Value, node parse.Node, name string, args []parse.Node, final reflect.Value) reflect.Value {
   512		if args != nil {
   513			args = args[1:] // Zeroth arg is function name/node; not passed to function.
   514		}
   515		typ := fun.Type()
   516		numIn := len(args)
   517		if final.IsValid() {
   518			numIn++
   519		}
   520		numFixed := len(args)
   521		if typ.IsVariadic() {
   522			numFixed = typ.NumIn() - 1 // last arg is the variadic one.
   523			if numIn < numFixed {
   524				s.errorf("wrong number of args for %s: want at least %d got %d", name, typ.NumIn()-1, len(args))
   525			}
   526		} else if numIn < typ.NumIn()-1 || !typ.IsVariadic() && numIn != typ.NumIn() {
   527			s.errorf("wrong number of args for %s: want %d got %d", name, typ.NumIn(), len(args))
   528		}
   529		if !goodFunc(typ) {
   530			// TODO: This could still be a confusing error; maybe goodFunc should provide info.
   531			s.errorf("can't call method/function %q with %d results", name, typ.NumOut())
   532		}
   533		// Build the arg list.
   534		argv := make([]reflect.Value, numIn)
   535		// Args must be evaluated. Fixed args first.
   536		i := 0
   537		for ; i < numFixed; i++ {
   538			argv[i] = s.evalArg(dot, typ.In(i), args[i])
   539		}
   540		// Now the ... args.
   541		if typ.IsVariadic() {
   542			argType := typ.In(typ.NumIn() - 1).Elem() // Argument is a slice.
   543			for ; i < len(args); i++ {
   544				argv[i] = s.evalArg(dot, argType, args[i])
   545			}
   546		}
   547		// Add final value if necessary.
   548		if final.IsValid() {
   549			t := typ.In(typ.NumIn() - 1)
   550			if typ.IsVariadic() {
   551				t = t.Elem()
   552			}
   553			argv[i] = s.validateType(final, t)
   554		}
   555		result := fun.Call(argv)
   556		// If we have an error that is not nil, stop execution and return that error to the caller.
   557		if len(result) == 2 && !result[1].IsNil() {
   558			s.at(node)
   559			s.errorf("error calling %s: %s", name, result[1].Interface().(error))
   560		}
   561		return result[0]
   562	}
   563	
   564	// canBeNil reports whether an untyped nil can be assigned to the type. See reflect.Zero.
   565	func canBeNil(typ reflect.Type) bool {
   566		switch typ.Kind() {
   567		case reflect.Chan, reflect.Func, reflect.Interface, reflect.Map, reflect.Ptr, reflect.Slice:
   568			return true
   569		}
   570		return false
   571	}
   572	
   573	// validateType guarantees that the value is valid and assignable to the type.
   574	func (s *state) validateType(value reflect.Value, typ reflect.Type) reflect.Value {
   575		if !value.IsValid() {
   576			if typ == nil || canBeNil(typ) {
   577				// An untyped nil interface{}. Accept as a proper nil value.
   578				return reflect.Zero(typ)
   579			}
   580			s.errorf("invalid value; expected %s", typ)
   581		}
   582		if typ != nil && !value.Type().AssignableTo(typ) {
   583			if value.Kind() == reflect.Interface && !value.IsNil() {
   584				value = value.Elem()
   585				if value.Type().AssignableTo(typ) {
   586					return value
   587				}
   588				// fallthrough
   589			}
   590			// Does one dereference or indirection work? We could do more, as we
   591			// do with method receivers, but that gets messy and method receivers
   592			// are much more constrained, so it makes more sense there than here.
   593			// Besides, one is almost always all you need.
   594			switch {
   595			case value.Kind() == reflect.Ptr && value.Type().Elem().AssignableTo(typ):
   596				value = value.Elem()
   597			case reflect.PtrTo(value.Type()).AssignableTo(typ) && value.CanAddr():
   598				value = value.Addr()
   599			default:
   600				s.errorf("wrong type for value; expected %s; got %s", typ, value.Type())
   601			}
   602		}
   603		return value
   604	}
   605	
   606	func (s *state) evalArg(dot reflect.Value, typ reflect.Type, n parse.Node) reflect.Value {
   607		s.at(n)
   608		switch arg := n.(type) {
   609		case *parse.DotNode:
   610			return s.validateType(dot, typ)
   611		case *parse.NilNode:
   612			if canBeNil(typ) {
   613				return reflect.Zero(typ)
   614			}
   615			s.errorf("cannot assign nil to %s", typ)
   616		case *parse.FieldNode:
   617			return s.validateType(s.evalFieldNode(dot, arg, []parse.Node{n}, zero), typ)
   618		case *parse.VariableNode:
   619			return s.validateType(s.evalVariableNode(dot, arg, nil, zero), typ)
   620		case *parse.PipeNode:
   621			return s.validateType(s.evalPipeline(dot, arg), typ)
   622		case *parse.IdentifierNode:
   623			return s.evalFunction(dot, arg, arg, nil, zero)
   624		}
   625		switch typ.Kind() {
   626		case reflect.Bool:
   627			return s.evalBool(typ, n)
   628		case reflect.Complex64, reflect.Complex128:
   629			return s.evalComplex(typ, n)
   630		case reflect.Float32, reflect.Float64:
   631			return s.evalFloat(typ, n)
   632		case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
   633			return s.evalInteger(typ, n)
   634		case reflect.Interface:
   635			if typ.NumMethod() == 0 {
   636				return s.evalEmptyInterface(dot, n)
   637			}
   638		case reflect.String:
   639			return s.evalString(typ, n)
   640		case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
   641			return s.evalUnsignedInteger(typ, n)
   642		}
   643		s.errorf("can't handle %s for arg of type %s", n, typ)
   644		panic("not reached")
   645	}
   646	
   647	func (s *state) evalBool(typ reflect.Type, n parse.Node) reflect.Value {
   648		s.at(n)
   649		if n, ok := n.(*parse.BoolNode); ok {
   650			value := reflect.New(typ).Elem()
   651			value.SetBool(n.True)
   652			return value
   653		}
   654		s.errorf("expected bool; found %s", n)
   655		panic("not reached")
   656	}
   657	
   658	func (s *state) evalString(typ reflect.Type, n parse.Node) reflect.Value {
   659		s.at(n)
   660		if n, ok := n.(*parse.StringNode); ok {
   661			value := reflect.New(typ).Elem()
   662			value.SetString(n.Text)
   663			return value
   664		}
   665		s.errorf("expected string; found %s", n)
   666		panic("not reached")
   667	}
   668	
   669	func (s *state) evalInteger(typ reflect.Type, n parse.Node) reflect.Value {
   670		s.at(n)
   671		if n, ok := n.(*parse.NumberNode); ok && n.IsInt {
   672			value := reflect.New(typ).Elem()
   673			value.SetInt(n.Int64)
   674			return value
   675		}
   676		s.errorf("expected integer; found %s", n)
   677		panic("not reached")
   678	}
   679	
   680	func (s *state) evalUnsignedInteger(typ reflect.Type, n parse.Node) reflect.Value {
   681		s.at(n)
   682		if n, ok := n.(*parse.NumberNode); ok && n.IsUint {
   683			value := reflect.New(typ).Elem()
   684			value.SetUint(n.Uint64)
   685			return value
   686		}
   687		s.errorf("expected unsigned integer; found %s", n)
   688		panic("not reached")
   689	}
   690	
   691	func (s *state) evalFloat(typ reflect.Type, n parse.Node) reflect.Value {
   692		s.at(n)
   693		if n, ok := n.(*parse.NumberNode); ok && n.IsFloat {
   694			value := reflect.New(typ).Elem()
   695			value.SetFloat(n.Float64)
   696			return value
   697		}
   698		s.errorf("expected float; found %s", n)
   699		panic("not reached")
   700	}
   701	
   702	func (s *state) evalComplex(typ reflect.Type, n parse.Node) reflect.Value {
   703		if n, ok := n.(*parse.NumberNode); ok && n.IsComplex {
   704			value := reflect.New(typ).Elem()
   705			value.SetComplex(n.Complex128)
   706			return value
   707		}
   708		s.errorf("expected complex; found %s", n)
   709		panic("not reached")
   710	}
   711	
   712	func (s *state) evalEmptyInterface(dot reflect.Value, n parse.Node) reflect.Value {
   713		s.at(n)
   714		switch n := n.(type) {
   715		case *parse.BoolNode:
   716			return reflect.ValueOf(n.True)
   717		case *parse.DotNode:
   718			return dot
   719		case *parse.FieldNode:
   720			return s.evalFieldNode(dot, n, nil, zero)
   721		case *parse.IdentifierNode:
   722			return s.evalFunction(dot, n, n, nil, zero)
   723		case *parse.NilNode:
   724			// NilNode is handled in evalArg, the only place that calls here.
   725			s.errorf("evalEmptyInterface: nil (can't happen)")
   726		case *parse.NumberNode:
   727			return s.idealConstant(n)
   728		case *parse.StringNode:
   729			return reflect.ValueOf(n.Text)
   730		case *parse.VariableNode:
   731			return s.evalVariableNode(dot, n, nil, zero)
   732		case *parse.PipeNode:
   733			return s.evalPipeline(dot, n)
   734		}
   735		s.errorf("can't handle assignment of %s to empty interface argument", n)
   736		panic("not reached")
   737	}
   738	
   739	// indirect returns the item at the end of indirection, and a bool to indicate if it's nil.
   740	// We indirect through pointers and empty interfaces (only) because
   741	// non-empty interfaces have methods we might need.
   742	func indirect(v reflect.Value) (rv reflect.Value, isNil bool) {
   743		for ; v.Kind() == reflect.Ptr || v.Kind() == reflect.Interface; v = v.Elem() {
   744			if v.IsNil() {
   745				return v, true
   746			}
   747			if v.Kind() == reflect.Interface && v.NumMethod() > 0 {
   748				break
   749			}
   750		}
   751		return v, false
   752	}
   753	
   754	// printValue writes the textual representation of the value to the output of
   755	// the template.
   756	func (s *state) printValue(n parse.Node, v reflect.Value) {
   757		s.at(n)
   758		iface, ok := printableValue(v)
   759		if !ok {
   760			s.errorf("can't print %s of type %s", n, v.Type())
   761		}
   762		fmt.Fprint(s.wr, iface)
   763	}
   764	
   765	// printableValue returns the, possibly indirected, interface value inside v that
   766	// is best for a call to formatted printer.
   767	func printableValue(v reflect.Value) (interface{}, bool) {
   768		if v.Kind() == reflect.Ptr {
   769			v, _ = indirect(v) // fmt.Fprint handles nil.
   770		}
   771		if !v.IsValid() {
   772			return "<no value>", true
   773		}
   774	
   775		if !v.Type().Implements(errorType) && !v.Type().Implements(fmtStringerType) {
   776			if v.CanAddr() && (reflect.PtrTo(v.Type()).Implements(errorType) || reflect.PtrTo(v.Type()).Implements(fmtStringerType)) {
   777				v = v.Addr()
   778			} else {
   779				switch v.Kind() {
   780				case reflect.Chan, reflect.Func:
   781					return nil, false
   782				}
   783			}
   784		}
   785		return v.Interface(), true
   786	}
   787	
   788	// Types to help sort the keys in a map for reproducible output.
   789	
   790	type rvs []reflect.Value
   791	
   792	func (x rvs) Len() int      { return len(x) }
   793	func (x rvs) Swap(i, j int) { x[i], x[j] = x[j], x[i] }
   794	
   795	type rvInts struct{ rvs }
   796	
   797	func (x rvInts) Less(i, j int) bool { return x.rvs[i].Int() < x.rvs[j].Int() }
   798	
   799	type rvUints struct{ rvs }
   800	
   801	func (x rvUints) Less(i, j int) bool { return x.rvs[i].Uint() < x.rvs[j].Uint() }
   802	
   803	type rvFloats struct{ rvs }
   804	
   805	func (x rvFloats) Less(i, j int) bool { return x.rvs[i].Float() < x.rvs[j].Float() }
   806	
   807	type rvStrings struct{ rvs }
   808	
   809	func (x rvStrings) Less(i, j int) bool { return x.rvs[i].String() < x.rvs[j].String() }
   810	
   811	// sortKeys sorts (if it can) the slice of reflect.Values, which is a slice of map keys.
   812	func sortKeys(v []reflect.Value) []reflect.Value {
   813		if len(v) <= 1 {
   814			return v
   815		}
   816		switch v[0].Kind() {
   817		case reflect.Float32, reflect.Float64:
   818			sort.Sort(rvFloats{v})
   819		case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
   820			sort.Sort(rvInts{v})
   821		case reflect.String:
   822			sort.Sort(rvStrings{v})
   823		case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
   824			sort.Sort(rvUints{v})
   825		}
   826		return v
   827	}

View as plain text