go exec 源码
golang exec 代码
文件路径：/src/text/template/exec.go
// 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"
"internal/fmtsort"
"io"
"reflect"
"runtime"
"strings"
"text/template/parse"
)
// 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 state 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 isTrue(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) evalFunction(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) evalField(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) evalCall(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
}
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