* config/mn10300/mn10300.md (adddi3_degenerate): Remove bogus

[official-gcc.git] / libgo / go / encoding / xml / marshal.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 xml

import (
        "bufio"
        "bytes"
        "encoding"
        "fmt"
        "io"
        "reflect"
        "strconv"
        "strings"
)

const (
        // Header is a generic XML header suitable for use with the output of Marshal.
        // This is not automatically added to any output of this package,
        // it is provided as a convenience.
        Header = `<?xml version="1.0" encoding="UTF-8"?>` + "\n"
)

// Marshal returns the XML encoding of v.
//
// Marshal handles an array or slice by marshaling each of the elements.
// Marshal handles a pointer by marshaling the value it points at or, if the
// pointer is nil, by writing nothing. Marshal handles an interface value by
// marshaling the value it contains or, if the interface value is nil, by
// writing nothing. Marshal handles all other data by writing one or more XML
// elements containing the data.
//
// The name for the XML elements is taken from, in order of preference:
//     - the tag on the XMLName field, if the data is a struct
//     - the value of the XMLName field of type Name
//     - the tag of the struct field used to obtain the data
//     - the name of the struct field used to obtain the data
//     - the name of the marshaled type
//
// The XML element for a struct contains marshaled elements for each of the
// exported fields of the struct, with these exceptions:
//     - the XMLName field, described above, is omitted.
//     - a field with tag "-" is omitted.
//     - a field with tag "name,attr" becomes an attribute with
//       the given name in the XML element.
//     - a field with tag ",attr" becomes an attribute with the
//       field name in the XML element.
//     - a field with tag ",chardata" is written as character data,
//       not as an XML element.
//     - a field with tag ",cdata" is written as character data
//       wrapped in one or more <![CDATA[ ... ]]> tags, not as an XML element.
//     - a field with tag ",innerxml" is written verbatim, not subject
//       to the usual marshaling procedure.
//     - a field with tag ",comment" is written as an XML comment, not
//       subject to the usual marshaling procedure. It must not contain
//       the "--" string within it.
//     - a field with a tag including the "omitempty" option is omitted
//       if the field value is empty. The empty values are false, 0, any
//       nil pointer or interface value, and any array, slice, map, or
//       string of length zero.
//     - an anonymous struct field is handled as if the fields of its
//       value were part of the outer struct.
//
// If a field uses a tag "a>b>c", then the element c will be nested inside
// parent elements a and b. Fields that appear next to each other that name
// the same parent will be enclosed in one XML element.
//
// If the XML name for a struct field is defined by both the field tag and the
// struct's XMLName field, the names must match.
//
// See MarshalIndent for an example.
//
// Marshal will return an error if asked to marshal a channel, function, or map.
func Marshal(v interface{}) ([]byte, error) {
        var b bytes.Buffer
        if err := NewEncoder(&b).Encode(v); err != nil {
                return nil, err
        }
        return b.Bytes(), nil
}

// Marshaler is the interface implemented by objects that can marshal
// themselves into valid XML elements.
//
// MarshalXML encodes the receiver as zero or more XML elements.
// By convention, arrays or slices are typically encoded as a sequence
// of elements, one per entry.
// Using start as the element tag is not required, but doing so
// will enable Unmarshal to match the XML elements to the correct
// struct field.
// One common implementation strategy is to construct a separate
// value with a layout corresponding to the desired XML and then
// to encode it using e.EncodeElement.
// Another common strategy is to use repeated calls to e.EncodeToken
// to generate the XML output one token at a time.
// The sequence of encoded tokens must make up zero or more valid
// XML elements.
type Marshaler interface {
        MarshalXML(e *Encoder, start StartElement) error
}

// MarshalerAttr is the interface implemented by objects that can marshal
// themselves into valid XML attributes.
//
// MarshalXMLAttr returns an XML attribute with the encoded value of the receiver.
// Using name as the attribute name is not required, but doing so
// will enable Unmarshal to match the attribute to the correct
// struct field.
// If MarshalXMLAttr returns the zero attribute Attr{}, no attribute
// will be generated in the output.
// MarshalXMLAttr is used only for struct fields with the
// "attr" option in the field tag.
type MarshalerAttr interface {
        MarshalXMLAttr(name Name) (Attr, error)
}

// MarshalIndent works like Marshal, but each XML element begins on a new
// indented line that starts with prefix and is followed by one or more
// copies of indent according to the nesting depth.
func MarshalIndent(v interface{}, prefix, indent string) ([]byte, error) {
        var b bytes.Buffer
        enc := NewEncoder(&b)
        enc.Indent(prefix, indent)
        if err := enc.Encode(v); err != nil {
                return nil, err
        }
        return b.Bytes(), nil
}

// An Encoder writes XML data to an output stream.
type Encoder struct {
        p printer
}

// NewEncoder returns a new encoder that writes to w.
func NewEncoder(w io.Writer) *Encoder {
        e := &Encoder{printer{Writer: bufio.NewWriter(w)}}
        e.p.encoder = e
        return e
}

// Indent sets the encoder to generate XML in which each element
// begins on a new indented line that starts with prefix and is followed by
// one or more copies of indent according to the nesting depth.
func (enc *Encoder) Indent(prefix, indent string) {
        enc.p.prefix = prefix
        enc.p.indent = indent
}

// Encode writes the XML encoding of v to the stream.
//
// See the documentation for Marshal for details about the conversion
// of Go values to XML.
//
// Encode calls Flush before returning.
func (enc *Encoder) Encode(v interface{}) error {
        err := enc.p.marshalValue(reflect.ValueOf(v), nil, nil)
        if err != nil {
                return err
        }
        return enc.p.Flush()
}

// EncodeElement writes the XML encoding of v to the stream,
// using start as the outermost tag in the encoding.
//
// See the documentation for Marshal for details about the conversion
// of Go values to XML.
//
// EncodeElement calls Flush before returning.
func (enc *Encoder) EncodeElement(v interface{}, start StartElement) error {
        err := enc.p.marshalValue(reflect.ValueOf(v), nil, &start)
        if err != nil {
                return err
        }
        return enc.p.Flush()
}

var (
        begComment  = []byte("<!--")
        endComment  = []byte("-->")
        endProcInst = []byte("?>")
)

// EncodeToken writes the given XML token to the stream.
// It returns an error if StartElement and EndElement tokens are not properly matched.
//
// EncodeToken does not call Flush, because usually it is part of a larger operation
// such as Encode or EncodeElement (or a custom Marshaler's MarshalXML invoked
// during those), and those will call Flush when finished.
// Callers that create an Encoder and then invoke EncodeToken directly, without
// using Encode or EncodeElement, need to call Flush when finished to ensure
// that the XML is written to the underlying writer.
//
// EncodeToken allows writing a ProcInst with Target set to "xml" only as the first token
// in the stream.
func (enc *Encoder) EncodeToken(t Token) error {

        p := &enc.p
        switch t := t.(type) {
        case StartElement:
                if err := p.writeStart(&t); err != nil {
                        return err
                }
        case EndElement:
                if err := p.writeEnd(t.Name); err != nil {
                        return err
                }
        case CharData:
                escapeText(p, t, false)
        case Comment:
                if bytes.Contains(t, endComment) {
                        return fmt.Errorf("xml: EncodeToken of Comment containing --> marker")
                }
                p.WriteString("<!--")
                p.Write(t)
                p.WriteString("-->")
                return p.cachedWriteError()
        case ProcInst:
                // First token to be encoded which is also a ProcInst with target of xml
                // is the xml declaration. The only ProcInst where target of xml is allowed.
                if t.Target == "xml" && p.Buffered() != 0 {
                        return fmt.Errorf("xml: EncodeToken of ProcInst xml target only valid for xml declaration, first token encoded")
                }
                if !isNameString(t.Target) {
                        return fmt.Errorf("xml: EncodeToken of ProcInst with invalid Target")
                }
                if bytes.Contains(t.Inst, endProcInst) {
                        return fmt.Errorf("xml: EncodeToken of ProcInst containing ?> marker")
                }
                p.WriteString("<?")
                p.WriteString(t.Target)
                if len(t.Inst) > 0 {
                        p.WriteByte(' ')
                        p.Write(t.Inst)
                }
                p.WriteString("?>")
        case Directive:
                if !isValidDirective(t) {
                        return fmt.Errorf("xml: EncodeToken of Directive containing wrong < or > markers")
                }
                p.WriteString("<!")
                p.Write(t)
                p.WriteString(">")
        default:
                return fmt.Errorf("xml: EncodeToken of invalid token type")

        }
        return p.cachedWriteError()
}

// isValidDirective reports whether dir is a valid directive text,
// meaning angle brackets are matched, ignoring comments and strings.
func isValidDirective(dir Directive) bool {
        var (
                depth     int
                inquote   uint8
                incomment bool
        )
        for i, c := range dir {
                switch {
                case incomment:
                        if c == '>' {
                                if n := 1 + i - len(endComment); n >= 0 && bytes.Equal(dir[n:i+1], endComment) {
                                        incomment = false
                                }
                        }
                        // Just ignore anything in comment
                case inquote != 0:
                        if c == inquote {
                                inquote = 0
                        }
                        // Just ignore anything within quotes
                case c == '\'' || c == '"':
                        inquote = c
                case c == '<':
                        if i+len(begComment) < len(dir) && bytes.Equal(dir[i:i+len(begComment)], begComment) {
                                incomment = true
                        } else {
                                depth++
                        }
                case c == '>':
                        if depth == 0 {
                                return false
                        }
                        depth--
                }
        }
        return depth == 0 && inquote == 0 && !incomment
}

// Flush flushes any buffered XML to the underlying writer.
// See the EncodeToken documentation for details about when it is necessary.
func (enc *Encoder) Flush() error {
        return enc.p.Flush()
}

type printer struct {
        *bufio.Writer
        encoder    *Encoder
        seq        int
        indent     string
        prefix     string
        depth      int
        indentedIn bool
        putNewline bool
        attrNS     map[string]string // map prefix -> name space
        attrPrefix map[string]string // map name space -> prefix
        prefixes   []string
        tags       []Name
}

// createAttrPrefix finds the name space prefix attribute to use for the given name space,
// defining a new prefix if necessary. It returns the prefix.
func (p *printer) createAttrPrefix(url string) string {
        if prefix := p.attrPrefix[url]; prefix != "" {
                return prefix
        }

        // The "http://www.w3.org/XML/1998/namespace" name space is predefined as "xml"
        // and must be referred to that way.
        // (The "http://www.w3.org/2000/xmlns/" name space is also predefined as "xmlns",
        // but users should not be trying to use that one directly - that's our job.)
        if url == xmlURL {
                return xmlPrefix
        }

        // Need to define a new name space.
        if p.attrPrefix == nil {
                p.attrPrefix = make(map[string]string)
                p.attrNS = make(map[string]string)
        }

        // Pick a name. We try to use the final element of the path
        // but fall back to _.
        prefix := strings.TrimRight(url, "/")
        if i := strings.LastIndex(prefix, "/"); i >= 0 {
                prefix = prefix[i+1:]
        }
        if prefix == "" || !isName([]byte(prefix)) || strings.Contains(prefix, ":") {
                prefix = "_"
        }
        if strings.HasPrefix(prefix, "xml") {
                // xmlanything is reserved.
                prefix = "_" + prefix
        }
        if p.attrNS[prefix] != "" {
                // Name is taken. Find a better one.
                for p.seq++; ; p.seq++ {
                        if id := prefix + "_" + strconv.Itoa(p.seq); p.attrNS[id] == "" {
                                prefix = id
                                break
                        }
                }
        }

        p.attrPrefix[url] = prefix
        p.attrNS[prefix] = url

        p.WriteString(`xmlns:`)
        p.WriteString(prefix)
        p.WriteString(`="`)
        EscapeText(p, []byte(url))
        p.WriteString(`" `)

        p.prefixes = append(p.prefixes, prefix)

        return prefix
}

// deleteAttrPrefix removes an attribute name space prefix.
func (p *printer) deleteAttrPrefix(prefix string) {
        delete(p.attrPrefix, p.attrNS[prefix])
        delete(p.attrNS, prefix)
}

func (p *printer) markPrefix() {
        p.prefixes = append(p.prefixes, "")
}

func (p *printer) popPrefix() {
        for len(p.prefixes) > 0 {
                prefix := p.prefixes[len(p.prefixes)-1]
                p.prefixes = p.prefixes[:len(p.prefixes)-1]
                if prefix == "" {
                        break
                }
                p.deleteAttrPrefix(prefix)
        }
}

var (
        marshalerType     = reflect.TypeOf((*Marshaler)(nil)).Elem()
        marshalerAttrType = reflect.TypeOf((*MarshalerAttr)(nil)).Elem()
        textMarshalerType = reflect.TypeOf((*encoding.TextMarshaler)(nil)).Elem()
)

// marshalValue writes one or more XML elements representing val.
// If val was obtained from a struct field, finfo must have its details.
func (p *printer) marshalValue(val reflect.Value, finfo *fieldInfo, startTemplate *StartElement) error {
        if startTemplate != nil && startTemplate.Name.Local == "" {
                return fmt.Errorf("xml: EncodeElement of StartElement with missing name")
        }

        if !val.IsValid() {
                return nil
        }
        if finfo != nil && finfo.flags&fOmitEmpty != 0 && isEmptyValue(val) {
                return nil
        }

        // Drill into interfaces and pointers.
        // This can turn into an infinite loop given a cyclic chain,
        // but it matches the Go 1 behavior.
        for val.Kind() == reflect.Interface || val.Kind() == reflect.Ptr {
                if val.IsNil() {
                        return nil
                }
                val = val.Elem()
        }

        kind := val.Kind()
        typ := val.Type()

        // Check for marshaler.
        if val.CanInterface() && typ.Implements(marshalerType) {
                return p.marshalInterface(val.Interface().(Marshaler), defaultStart(typ, finfo, startTemplate))
        }
        if val.CanAddr() {
                pv := val.Addr()
                if pv.CanInterface() && pv.Type().Implements(marshalerType) {
                        return p.marshalInterface(pv.Interface().(Marshaler), defaultStart(pv.Type(), finfo, startTemplate))
                }
        }

        // Check for text marshaler.
        if val.CanInterface() && typ.Implements(textMarshalerType) {
                return p.marshalTextInterface(val.Interface().(encoding.TextMarshaler), defaultStart(typ, finfo, startTemplate))
        }
        if val.CanAddr() {
                pv := val.Addr()
                if pv.CanInterface() && pv.Type().Implements(textMarshalerType) {
                        return p.marshalTextInterface(pv.Interface().(encoding.TextMarshaler), defaultStart(pv.Type(), finfo, startTemplate))
                }
        }

        // Slices and arrays iterate over the elements. They do not have an enclosing tag.
        if (kind == reflect.Slice || kind == reflect.Array) && typ.Elem().Kind() != reflect.Uint8 {
                for i, n := 0, val.Len(); i < n; i++ {
                        if err := p.marshalValue(val.Index(i), finfo, startTemplate); err != nil {
                                return err
                        }
                }
                return nil
        }

        tinfo, err := getTypeInfo(typ)
        if err != nil {
                return err
        }

        // Create start element.
        // Precedence for the XML element name is:
        // 0. startTemplate
        // 1. XMLName field in underlying struct;
        // 2. field name/tag in the struct field; and
        // 3. type name
        var start StartElement

        if startTemplate != nil {
                start.Name = startTemplate.Name
                start.Attr = append(start.Attr, startTemplate.Attr...)
        } else if tinfo.xmlname != nil {
                xmlname := tinfo.xmlname
                if xmlname.name != "" {
                        start.Name.Space, start.Name.Local = xmlname.xmlns, xmlname.name
                } else if v, ok := xmlname.value(val).Interface().(Name); ok && v.Local != "" {
                        start.Name = v
                }
        }
        if start.Name.Local == "" && finfo != nil {
                start.Name.Space, start.Name.Local = finfo.xmlns, finfo.name
        }
        if start.Name.Local == "" {
                name := typ.Name()
                if name == "" {
                        return &UnsupportedTypeError{typ}
                }
                start.Name.Local = name
        }

        // Attributes
        for i := range tinfo.fields {
                finfo := &tinfo.fields[i]
                if finfo.flags&fAttr == 0 {
                        continue
                }
                fv := finfo.value(val)

                if finfo.flags&fOmitEmpty != 0 && isEmptyValue(fv) {
                        continue
                }

                if fv.Kind() == reflect.Interface && fv.IsNil() {
                        continue
                }

                name := Name{Space: finfo.xmlns, Local: finfo.name}
                if err := p.marshalAttr(&start, name, fv); err != nil {
                        return err
                }
        }

        if err := p.writeStart(&start); err != nil {
                return err
        }

        if val.Kind() == reflect.Struct {
                err = p.marshalStruct(tinfo, val)
        } else {
                s, b, err1 := p.marshalSimple(typ, val)
                if err1 != nil {
                        err = err1
                } else if b != nil {
                        EscapeText(p, b)
                } else {
                        p.EscapeString(s)
                }
        }
        if err != nil {
                return err
        }

        if err := p.writeEnd(start.Name); err != nil {
                return err
        }

        return p.cachedWriteError()
}

// marshalAttr marshals an attribute with the given name and value, adding to start.Attr.
func (p *printer) marshalAttr(start *StartElement, name Name, val reflect.Value) error {
        if val.CanInterface() && val.Type().Implements(marshalerAttrType) {
                attr, err := val.Interface().(MarshalerAttr).MarshalXMLAttr(name)
                if err != nil {
                        return err
                }
                if attr.Name.Local != "" {
                        start.Attr = append(start.Attr, attr)
                }
                return nil
        }

        if val.CanAddr() {
                pv := val.Addr()
                if pv.CanInterface() && pv.Type().Implements(marshalerAttrType) {
                        attr, err := pv.Interface().(MarshalerAttr).MarshalXMLAttr(name)
                        if err != nil {
                                return err
                        }
                        if attr.Name.Local != "" {
                                start.Attr = append(start.Attr, attr)
                        }
                        return nil
                }
        }

        if val.CanInterface() && val.Type().Implements(textMarshalerType) {
                text, err := val.Interface().(encoding.TextMarshaler).MarshalText()
                if err != nil {
                        return err
                }
                start.Attr = append(start.Attr, Attr{name, string(text)})
                return nil
        }

        if val.CanAddr() {
                pv := val.Addr()
                if pv.CanInterface() && pv.Type().Implements(textMarshalerType) {
                        text, err := pv.Interface().(encoding.TextMarshaler).MarshalText()
                        if err != nil {
                                return err
                        }
                        start.Attr = append(start.Attr, Attr{name, string(text)})
                        return nil
                }
        }

        // Dereference or skip nil pointer, interface values.
        switch val.Kind() {
        case reflect.Ptr, reflect.Interface:
                if val.IsNil() {
                        return nil
                }
                val = val.Elem()
        }

        // Walk slices.
        if val.Kind() == reflect.Slice && val.Type().Elem().Kind() != reflect.Uint8 {
                n := val.Len()
                for i := 0; i < n; i++ {
                        if err := p.marshalAttr(start, name, val.Index(i)); err != nil {
                                return err
                        }
                }
                return nil
        }

        if val.Type() == attrType {
                start.Attr = append(start.Attr, val.Interface().(Attr))
                return nil
        }

        s, b, err := p.marshalSimple(val.Type(), val)
        if err != nil {
                return err
        }
        if b != nil {
                s = string(b)
        }
        start.Attr = append(start.Attr, Attr{name, s})
        return nil
}

// defaultStart returns the default start element to use,
// given the reflect type, field info, and start template.
func defaultStart(typ reflect.Type, finfo *fieldInfo, startTemplate *StartElement) StartElement {
        var start StartElement
        // Precedence for the XML element name is as above,
        // except that we do not look inside structs for the first field.
        if startTemplate != nil {
                start.Name = startTemplate.Name
                start.Attr = append(start.Attr, startTemplate.Attr...)
        } else if finfo != nil && finfo.name != "" {
                start.Name.Local = finfo.name
                start.Name.Space = finfo.xmlns
        } else if typ.Name() != "" {
                start.Name.Local = typ.Name()
        } else {
                // Must be a pointer to a named type,
                // since it has the Marshaler methods.
                start.Name.Local = typ.Elem().Name()
        }
        return start
}

// marshalInterface marshals a Marshaler interface value.
func (p *printer) marshalInterface(val Marshaler, start StartElement) error {
        // Push a marker onto the tag stack so that MarshalXML
        // cannot close the XML tags that it did not open.
        p.tags = append(p.tags, Name{})
        n := len(p.tags)

        err := val.MarshalXML(p.encoder, start)
        if err != nil {
                return err
        }

        // Make sure MarshalXML closed all its tags. p.tags[n-1] is the mark.
        if len(p.tags) > n {
                return fmt.Errorf("xml: %s.MarshalXML wrote invalid XML: <%s> not closed", receiverType(val), p.tags[len(p.tags)-1].Local)
        }
        p.tags = p.tags[:n-1]
        return nil
}

// marshalTextInterface marshals a TextMarshaler interface value.
func (p *printer) marshalTextInterface(val encoding.TextMarshaler, start StartElement) error {
        if err := p.writeStart(&start); err != nil {
                return err
        }
        text, err := val.MarshalText()
        if err != nil {
                return err
        }
        EscapeText(p, text)
        return p.writeEnd(start.Name)
}

// writeStart writes the given start element.
func (p *printer) writeStart(start *StartElement) error {
        if start.Name.Local == "" {
                return fmt.Errorf("xml: start tag with no name")
        }

        p.tags = append(p.tags, start.Name)
        p.markPrefix()

        p.writeIndent(1)
        p.WriteByte('<')
        p.WriteString(start.Name.Local)

        if start.Name.Space != "" {
                p.WriteString(` xmlns="`)
                p.EscapeString(start.Name.Space)
                p.WriteByte('"')
        }

        // Attributes
        for _, attr := range start.Attr {
                name := attr.Name
                if name.Local == "" {
                        continue
                }
                p.WriteByte(' ')
                if name.Space != "" {
                        p.WriteString(p.createAttrPrefix(name.Space))
                        p.WriteByte(':')
                }
                p.WriteString(name.Local)
                p.WriteString(`="`)
                p.EscapeString(attr.Value)
                p.WriteByte('"')
        }
        p.WriteByte('>')
        return nil
}

func (p *printer) writeEnd(name Name) error {
        if name.Local == "" {
                return fmt.Errorf("xml: end tag with no name")
        }
        if len(p.tags) == 0 || p.tags[len(p.tags)-1].Local == "" {
                return fmt.Errorf("xml: end tag </%s> without start tag", name.Local)
        }
        if top := p.tags[len(p.tags)-1]; top != name {
                if top.Local != name.Local {
                        return fmt.Errorf("xml: end tag </%s> does not match start tag <%s>", name.Local, top.Local)
                }
                return fmt.Errorf("xml: end tag </%s> in namespace %s does not match start tag <%s> in namespace %s", name.Local, name.Space, top.Local, top.Space)
        }
        p.tags = p.tags[:len(p.tags)-1]

        p.writeIndent(-1)
        p.WriteByte('<')
        p.WriteByte('/')
        p.WriteString(name.Local)
        p.WriteByte('>')
        p.popPrefix()
        return nil
}

func (p *printer) marshalSimple(typ reflect.Type, val reflect.Value) (string, []byte, error) {
        switch val.Kind() {
        case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
                return strconv.FormatInt(val.Int(), 10), nil, nil
        case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
                return strconv.FormatUint(val.Uint(), 10), nil, nil
        case reflect.Float32, reflect.Float64:
                return strconv.FormatFloat(val.Float(), 'g', -1, val.Type().Bits()), nil, nil
        case reflect.String:
                return val.String(), nil, nil
        case reflect.Bool:
                return strconv.FormatBool(val.Bool()), nil, nil
        case reflect.Array:
                if typ.Elem().Kind() != reflect.Uint8 {
                        break
                }
                // [...]byte
                var bytes []byte
                if val.CanAddr() {
                        bytes = val.Slice(0, val.Len()).Bytes()
                } else {
                        bytes = make([]byte, val.Len())
                        reflect.Copy(reflect.ValueOf(bytes), val)
                }
                return "", bytes, nil
        case reflect.Slice:
                if typ.Elem().Kind() != reflect.Uint8 {
                        break
                }
                // []byte
                return "", val.Bytes(), nil
        }
        return "", nil, &UnsupportedTypeError{typ}
}

var ddBytes = []byte("--")

// indirect drills into interfaces and pointers, returning the pointed-at value.
// If it encounters a nil interface or pointer, indirect returns that nil value.
// This can turn into an infinite loop given a cyclic chain,
// but it matches the Go 1 behavior.
func indirect(vf reflect.Value) reflect.Value {
        for vf.Kind() == reflect.Interface || vf.Kind() == reflect.Ptr {
                if vf.IsNil() {
                        return vf
                }
                vf = vf.Elem()
        }
        return vf
}

func (p *printer) marshalStruct(tinfo *typeInfo, val reflect.Value) error {
        s := parentStack{p: p}
        for i := range tinfo.fields {
                finfo := &tinfo.fields[i]
                if finfo.flags&fAttr != 0 {
                        continue
                }
                vf := finfo.value(val)

                switch finfo.flags & fMode {
                case fCDATA, fCharData:
                        emit := EscapeText
                        if finfo.flags&fMode == fCDATA {
                                emit = emitCDATA
                        }
                        if err := s.trim(finfo.parents); err != nil {
                                return err
                        }
                        if vf.CanInterface() && vf.Type().Implements(textMarshalerType) {
                                data, err := vf.Interface().(encoding.TextMarshaler).MarshalText()
                                if err != nil {
                                        return err
                                }
                                if err := emit(p, data); err != nil {
                                        return err
                                }
                                continue
                        }
                        if vf.CanAddr() {
                                pv := vf.Addr()
                                if pv.CanInterface() && pv.Type().Implements(textMarshalerType) {
                                        data, err := pv.Interface().(encoding.TextMarshaler).MarshalText()
                                        if err != nil {
                                                return err
                                        }
                                        if err := emit(p, data); err != nil {
                                                return err
                                        }
                                        continue
                                }
                        }

                        var scratch [64]byte
                        vf = indirect(vf)
                        switch vf.Kind() {
                        case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
                                if err := emit(p, strconv.AppendInt(scratch[:0], vf.Int(), 10)); err != nil {
                                        return err
                                }
                        case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
                                if err := emit(p, strconv.AppendUint(scratch[:0], vf.Uint(), 10)); err != nil {
                                        return err
                                }
                        case reflect.Float32, reflect.Float64:
                                if err := emit(p, strconv.AppendFloat(scratch[:0], vf.Float(), 'g', -1, vf.Type().Bits())); err != nil {
                                        return err
                                }
                        case reflect.Bool:
                                if err := emit(p, strconv.AppendBool(scratch[:0], vf.Bool())); err != nil {
                                        return err
                                }
                        case reflect.String:
                                if err := emit(p, []byte(vf.String())); err != nil {
                                        return err
                                }
                        case reflect.Slice:
                                if elem, ok := vf.Interface().([]byte); ok {
                                        if err := emit(p, elem); err != nil {
                                                return err
                                        }
                                }
                        }
                        continue

                case fComment:
                        if err := s.trim(finfo.parents); err != nil {
                                return err
                        }
                        vf = indirect(vf)
                        k := vf.Kind()
                        if !(k == reflect.String || k == reflect.Slice && vf.Type().Elem().Kind() == reflect.Uint8) {
                                return fmt.Errorf("xml: bad type for comment field of %s", val.Type())
                        }
                        if vf.Len() == 0 {
                                continue
                        }
                        p.writeIndent(0)
                        p.WriteString("<!--")
                        dashDash := false
                        dashLast := false
                        switch k {
                        case reflect.String:
                                s := vf.String()
                                dashDash = strings.Contains(s, "--")
                                dashLast = s[len(s)-1] == '-'
                                if !dashDash {
                                        p.WriteString(s)
                                }
                        case reflect.Slice:
                                b := vf.Bytes()
                                dashDash = bytes.Contains(b, ddBytes)
                                dashLast = b[len(b)-1] == '-'
                                if !dashDash {
                                        p.Write(b)
                                }
                        default:
                                panic("can't happen")
                        }
                        if dashDash {
                                return fmt.Errorf(`xml: comments must not contain "--"`)
                        }
                        if dashLast {
                                // "--->" is invalid grammar. Make it "- -->"
                                p.WriteByte(' ')
                        }
                        p.WriteString("-->")
                        continue

                case fInnerXml:
                        vf = indirect(vf)
                        iface := vf.Interface()
                        switch raw := iface.(type) {
                        case []byte:
                                p.Write(raw)
                                continue
                        case string:
                                p.WriteString(raw)
                                continue
                        }

                case fElement, fElement | fAny:
                        if err := s.trim(finfo.parents); err != nil {
                                return err
                        }
                        if len(finfo.parents) > len(s.stack) {
                                if vf.Kind() != reflect.Ptr && vf.Kind() != reflect.Interface || !vf.IsNil() {
                                        if err := s.push(finfo.parents[len(s.stack):]); err != nil {
                                                return err
                                        }
                                }
                        }
                }
                if err := p.marshalValue(vf, finfo, nil); err != nil {
                        return err
                }
        }
        s.trim(nil)
        return p.cachedWriteError()
}

// return the bufio Writer's cached write error
func (p *printer) cachedWriteError() error {
        _, err := p.Write(nil)
        return err
}

func (p *printer) writeIndent(depthDelta int) {
        if len(p.prefix) == 0 && len(p.indent) == 0 {
                return
        }
        if depthDelta < 0 {
                p.depth--
                if p.indentedIn {
                        p.indentedIn = false
                        return
                }
                p.indentedIn = false
        }
        if p.putNewline {
                p.WriteByte('\n')
        } else {
                p.putNewline = true
        }
        if len(p.prefix) > 0 {
                p.WriteString(p.prefix)
        }
        if len(p.indent) > 0 {
                for i := 0; i < p.depth; i++ {
                        p.WriteString(p.indent)
                }
        }
        if depthDelta > 0 {
                p.depth++
                p.indentedIn = true
        }
}

type parentStack struct {
        p     *printer
        stack []string
}

// trim updates the XML context to match the longest common prefix of the stack
// and the given parents. A closing tag will be written for every parent
// popped. Passing a zero slice or nil will close all the elements.
func (s *parentStack) trim(parents []string) error {
        split := 0
        for ; split < len(parents) && split < len(s.stack); split++ {
                if parents[split] != s.stack[split] {
                        break
                }
        }
        for i := len(s.stack) - 1; i >= split; i-- {
                if err := s.p.writeEnd(Name{Local: s.stack[i]}); err != nil {
                        return err
                }
        }
        s.stack = s.stack[:split]
        return nil
}

// push adds parent elements to the stack and writes open tags.
func (s *parentStack) push(parents []string) error {
        for i := 0; i < len(parents); i++ {
                if err := s.p.writeStart(&StartElement{Name: Name{Local: parents[i]}}); err != nil {
                        return err
                }
        }
        s.stack = append(s.stack, parents...)
        return nil
}

// UnsupportedTypeError is returned when Marshal encounters a type
// that cannot be converted into XML.
type UnsupportedTypeError struct {
        Type reflect.Type
}

func (e *UnsupportedTypeError) Error() string {
        return "xml: unsupported type: " + e.Type.String()
}

func isEmptyValue(v reflect.Value) bool {
        switch v.Kind() {
        case reflect.Array, reflect.Map, reflect.Slice, reflect.String:
                return v.Len() == 0
        case reflect.Bool:
                return !v.Bool()
        case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
                return v.Int() == 0
        case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
                return v.Uint() == 0
        case reflect.Float32, reflect.Float64:
                return v.Float() == 0
        case reflect.Interface, reflect.Ptr:
                return v.IsNil()
        }
        return false
}