initial support for marshaling self-closing XML tags

add ,selfclosing flag to xml struct tags

support ,selfclosing flag on XMLName fields

Author: ydnar

marshal.go

@@ -211,8 +211,12 @@ func (enc *Encoder) EncodeToken(t Token) error {
 
 	p := &enc.p
 	switch t := t.(type) {
+	case SelfClosingElement:
+		if err := p.writeStart((*StartElement)(&t), true); err != nil {
+			return err
+		}
 	case StartElement:
-		if err := p.writeStart(&t); err != nil {
+		if err := p.writeStart(&t, false); err != nil {
 			return err
 		}
 	case EndElement:
@@ -593,7 +597,16 @@ func (p *printer) marshalValue(val reflect.Value, finfo *fieldInfo, startTemplat
 		start.Attr = append(start.Attr, Attr{Name{Space: "", Local: xmlnsPrefix}, ""})
 	}
 
-	if err := p.writeStart(&start); err != nil {
+	// If this is a self-closing tag, write the tag and return.
+	if finfo != nil && finfo.flags&fSelfClosing != 0 ||
+		tinfo.xmlname != nil && tinfo.xmlname.flags&fSelfClosing != 0 {
+		if err := p.writeStart(&start, true); err != nil {
+			return err
+		}
+		return p.cachedWriteError()
+	}
+
+	if err := p.writeStart(&start, false); err != nil {
 		return err
 	}
 
@@ -748,7 +761,7 @@ func (p *printer) marshalInterface(val Marshaler, start StartElement) error {
 
 // marshalTextInterface marshals a TextMarshaler interface value.
 func (p *printer) marshalTextInterface(val encoding.TextMarshaler, start StartElement) error {
-	if err := p.writeStart(&start); err != nil {
+	if err := p.writeStart(&start, false); err != nil {
 		return err
 	}
 	text, err := val.MarshalText()
@@ -760,7 +773,8 @@ func (p *printer) marshalTextInterface(val encoding.TextMarshaler, start StartEl
 }
 
 // writeStart writes the given start element.
-func (p *printer) writeStart(start *StartElement) error {
+// If close is true, it is written as a self-closing element.
+func (p *printer) writeStart(start *StartElement, close bool) error {
 	if start.Name.Local == "" {
 		return fmt.Errorf("xml: start tag with no name")
 	}
@@ -858,7 +872,13 @@ func (p *printer) writeStart(start *StartElement) error {
 		p.EscapeString(attr.Value)
 		p.WriteByte('"')
 	}
-	p.WriteByte('>')
+	if close {
+		p.WriteString("/>")
+		// Pop elements stack
+		p.elements = p.elements[:len(p.elements)-1]
+	} else {
+		p.WriteByte('>')
+	}
 	return nil
 }
 
@@ -1217,7 +1237,7 @@ func (s *parentStack) trim(parents []string) error {
 // 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 {
+		if err := s.p.writeStart(&StartElement{Name: Name{Local: parents[i]}}, false); err != nil {
 			return err
 		}
 	}

marshal_test.go

@@ -530,9 +530,17 @@ type Generic[T any] struct {
 
 type EPP struct {
 	XMLName struct{} `xml:"urn:ietf:params:xml:ns:epp-1.0 epp"`
+	Hello   *Hello   `xml:"hello,omitempty,selfclosing"`
 	Command *Command `xml:"command,omitempty"`
 }
 
+type Hello struct{}
+
+type Closer struct {
+	XMLName  struct{} `xml:"closer,selfclosing"`
+	Beverage string   `xml:"beverage,attr,omitempty"`
+}
+
 type Command struct {
 	Check *Check `xml:"urn:ietf:params:xml:ns:epp-1.0 check,omitempty"`
 }
@@ -1698,11 +1706,25 @@ var marshalTests = []struct {
 		UnmarshalOnly: true,
 	},
 
+	// Test self-closing tags
+	{
+		ExpectXML: `<closer/>`,
+		Value:     &Closer{},
+	},
+	{
+		ExpectXML: `<closer beverage="coffee"/>`,
+		Value:     &Closer{Beverage: "coffee"},
+	},
+
 	// Test namespace prefixes
 	{
 		ExpectXML: `<epp xmlns="urn:ietf:params:xml:ns:epp-1.0"></epp>`,
 		Value:     &EPP{},
 	},
+	{
+		ExpectXML: `<epp xmlns="urn:ietf:params:xml:ns:epp-1.0"><hello/></epp>`,
+		Value:     &EPP{Hello: &Hello{}},
+	},
 	{
 		ExpectXML: `<epp xmlns="urn:ietf:params:xml:ns:epp-1.0"><command></command></epp>`,
 		Value:     &EPP{Command: &Command{}},
@@ -2065,6 +2087,22 @@ var encodeTokenTests = []struct {
 		StartElement{Name{"space", "local"}, nil},
 	},
 	want: `<local xmlns="space">`,
+}, {
+	desc: "self-closing element with namespace",
+	toks: []Token{
+		SelfClosingElement{Name{"space", "local"}, nil},
+	},
+	want: `<local xmlns="space"/>`,
+}, {
+	desc: "self-closing elements inside other elements",
+	toks: []Token{
+		StartElement{Name{"", "outer"}, nil},
+		SelfClosingElement{Name{"", "a"}, nil},
+		SelfClosingElement{Name{"", "b"}, nil},
+		SelfClosingElement{Name{"", "c"}, nil},
+		EndElement{Name{"", "outer"}},
+	},
+	want: `<outer><a/><b/><c/></outer>`,
 }, {
 	desc: "start element with no name",
 	toks: []Token{

typeinfo.go

@@ -40,6 +40,8 @@ const (
 
 	fOmitEmpty
 
+	fSelfClosing
+
 	fMode = fElement | fAttr | fCDATA | fCharData | fInnerXML | fComment | fAny
 
 	xmlName = "XMLName"
@@ -140,6 +142,8 @@ func structFieldInfo(typ reflect.Type, f *reflect.StructField) (*fieldInfo, erro
 				finfo.flags |= fAny
 			case "omitempty":
 				finfo.flags |= fOmitEmpty
+			case "selfclosing":
+				finfo.flags |= fSelfClosing
 			}
 		}
 
@@ -162,6 +166,9 @@ func structFieldInfo(typ reflect.Type, f *reflect.StructField) (*fieldInfo, erro
 		if finfo.flags&fOmitEmpty != 0 && finfo.flags&(fElement|fAttr) == 0 {
 			valid = false
 		}
+		if finfo.flags&fSelfClosing != 0 && finfo.flags&fElement == 0 {
+			valid = false
+		}
 		if !valid {
 			return nil, fmt.Errorf("xml: invalid tag in field %s of type %s: %q",
 				f.Name, typ, f.Tag.Get("xml"))

xml.go

@@ -73,6 +73,18 @@ func (e StartElement) End() EndElement {
 	return EndElement{e.Name}
 }
 
+// A SelfClosingElement represents a self-closing XML element.
+// It is otherwise identical to StartElement.
+type SelfClosingElement StartElement
+
+// Copy creates a new copy of SelfClosingElement.
+func (e SelfClosingElement) Copy() SelfClosingElement {
+	attrs := make([]Attr, len(e.Attr))
+	copy(attrs, e.Attr)
+	e.Attr = attrs
+	return e
+}
+
 // An EndElement represents an XML end element.
 type EndElement struct {
 	Name Name