adding proto2 group

field.go

@@ -10,7 +10,7 @@ type Field struct {
 	Options  []*Option
 }
 
-// NormalField
+// NormalField represents a field in a Message.
 type NormalField struct {
 	*Field
 	Repeated bool

formatter.go

@@ -164,3 +164,8 @@ func (f *Formatter) VisitNormalField(f1 *NormalField) {
 	}
 	fmt.Fprintf(f.w, "%s %s = %d;\n", f1.Type, f1.Name, f1.Sequence)
 }
+
+// VisitGroup formats a proto2 Group.
+func (f *Formatter) VisitGroup(g *Group) {
+	io.WriteString(f.w, "TODO group ")
+}

group.go

@@ -0,0 +1,42 @@
+package proto
+
+// Group represents a (proto2 only) group.
+// https://developers.google.com/protocol-buffers/docs/reference/proto2-spec#group_field
+type Group struct {
+	Name     string
+	Sequence int
+	Elements []Visitee
+}
+
+// Accept dispatches the call to the visitor.
+func (g *Group) Accept(v Visitor) {
+	v.VisitGroup(g)
+}
+
+// addElement is part of elementContainer
+func (g *Group) addElement(v Visitee) {
+	g.Elements = append(g.Elements, v)
+}
+
+// parse expects:
+// group = label "group" groupName "=" fieldNumber messageBody
+func (g *Group) parse(p *Parser) error {
+	tok, lit := p.scanIgnoreWhitespace()
+	if tok != tIDENT {
+		if !isKeyword(tok) {
+			return p.unexpected(lit, "group name", g)
+		}
+	}
+	g.Name = lit
+	tok, lit = p.scanIgnoreWhitespace()
+	if tok != tEQUALS {
+		return p.unexpected(lit, "group =", g)
+	}
+	i, err := p.s.scanInteger()
+	if err != nil {
+		return p.unexpected(lit, "group sequence number", g)
+	}
+	g.Sequence = i
+	parseMessageBody(p, g)
+	return nil
+}

message.go

@@ -11,6 +11,11 @@ func (m *Message) Accept(v Visitor) {
 	v.VisitMessage(m)
 }
 
+// addElement is part of elementContainer
+func (m *Message) addElement(v Visitee) {
+	m.Elements = append(m.Elements, v)
+}
+
 func (m *Message) parse(p *Parser) error {
 	tok, lit := p.scanIgnoreWhitespace()
 	if tok != tIDENT {
@@ -23,47 +28,63 @@ func (m *Message) parse(p *Parser) error {
 	if tok != tLEFTCURLY {
 		return p.unexpected(lit, "message opening {", m)
 	}
+	return parseMessageBody(p, m)
+}
+
+func parseMessageBody(p *Parser, c elementContainer) error {
+	var (
+		tok token
+		lit string
+	)
 	for {
 		tok, lit = p.scanIgnoreWhitespace()
 		switch tok {
 		case tCOMMENT:
-			m.Elements = append(m.Elements, p.newComment(lit))
+			c.addElement(p.newComment(lit))
 		case tENUM:
 			e := new(Enum)
 			if err := e.parse(p); err != nil {
 				return err
 			}
-			m.Elements = append(m.Elements, e)
+			c.addElement(e)
 		case tMESSAGE:
 			msg := new(Message)
 			if err := msg.parse(p); err != nil {
 				return err
 			}
-			m.Elements = append(m.Elements, msg)
+			c.addElement(msg)
 		case tOPTION:
 			o := new(Option)
 			if err := o.parse(p); err != nil {
 				return err
 			}
-			m.Elements = append(m.Elements, o)
+			c.addElement(o)
 		case tONEOF:
 			o := new(Oneof)
 			if err := o.parse(p); err != nil {
 				return err
 			}
-			m.Elements = append(m.Elements, o)
+			c.addElement(o)
 		case tMAP:
 			f := newMapField()
 			if err := f.parse(p); err != nil {
 				return err
 			}
-			m.Elements = append(m.Elements, f)
+			c.addElement(f)
 		case tRESERVED:
 			r := new(Reserved)
 			if err := r.parse(p); err != nil {
 				return err
 			}
-			m.Elements = append(m.Elements, r)
+			c.addElement(r)
+		// BEGIN proto2 only
+		case tGROUP:
+			g := new(Group)
+			if err := g.parse(p); err != nil {
+				return err
+			}
+			c.addElement(g)
+		// END proto2 only
 		case tRIGHTCURLY:
 			goto done
 		case tSEMICOLON:
@@ -75,12 +96,12 @@ func (m *Message) parse(p *Parser) error {
 			if err := f.parse(p); err != nil {
 				return err
 			}
-			m.Elements = append(m.Elements, f)
+			c.addElement(f)
 		}
 	}
 done:
 	if tok != tRIGHTCURLY {
-		return p.unexpected(lit, "message closing }", m)
+		return p.unexpected(lit, "message|group closing }", c)
 	}
 	return nil
 }

proto.go

@@ -7,21 +7,6 @@ type Proto struct {
 	Elements []Visitee
 }
 
-// Comment holds a message and line number.
-type Comment struct {
-	Message string
-}
-
-// Accept dispatches the call to the visitor.
-func (c *Comment) Accept(v Visitor) {
-	v.VisitComment(c)
-}
-
-// IsMultiline returns whether its message has one or more lineends.
-func (c Comment) IsMultiline() bool {
-	return strings.Contains(c.Message, "\n")
-}
-
 // parse parsers a complete .proto definition source.
 func (proto *Proto) parse(p *Parser) error {
 	for {
@@ -82,3 +67,22 @@ func (proto *Proto) parse(p *Parser) error {
 done:
 	return nil
 }
+
+// Comment holds a message and line number.
+type Comment struct {
+	Message string
+}
+
+// Accept dispatches the call to the visitor.
+func (c *Comment) Accept(v Visitor) {
+	v.VisitComment(c)
+}
+
+// IsMultiline returns whether its message has one or more lineends.
+func (c Comment) IsMultiline() bool {
+	return strings.Contains(c.Message, "\n")
+}
+
+type elementContainer interface {
+	addElement(v Visitee)
+}

scanner.go

@@ -96,19 +96,6 @@ func (s *scanner) scanWhitespace() (tok token, lit string) {
 	return tWS, buf.String()
 }
 
-// skipWhitespace consumes all contiguous whitespace.
-func (s *scanner) skipWhitespace() {
-	// Non-whitespace characters and EOF will cause the loop to exit.
-	for {
-		if ch := s.read(); ch == eof {
-			break
-		} else if !isWhitespace(ch) {
-			s.unread(ch)
-			break
-		}
-	}
-}
-
 func (s *scanner) scanInteger() (int, error) {
 	var i int
 	if _, err := fmt.Fscanf(s.r, "%d", &i); err != nil {

token.go

@@ -30,7 +30,7 @@ const (
 	tDOT         // .
 
 	// Keywords
-	KeywordsStart
+	keywordsStart
 	tSYNTAX
 	tSERVICE
 	tRPC
@@ -52,9 +52,10 @@ const (
 	// proto2
 	tOPTIONAL
 	tGROUP
-	KeywordsEnd
+	keywordsEnd
 )
 
+// typeTokens exists for future validation
 const typeTokens = "double float int32 int64 uint32 uint64 sint32 sint64 fixed32 sfixed32 sfixed64 bool string bytes"
 
 // context dependent reserved words
@@ -64,5 +65,5 @@ const (
 
 // isKeyword returns if tok is in the keywords range
 func isKeyword(tok token) bool {
-	return KeywordsStart < tok && tok < KeywordsEnd
+	return keywordsStart < tok && tok < keywordsEnd
 }

visitor.go

@@ -17,6 +17,7 @@ type Visitor interface {
 	VisitReserved(r *Reserved)
 	VisitRPC(r *RPC)
 	VisitMapField(f *MapField)
+	VisitGroup(g *Group)
 }
 
 // Visitee is implemented by all Proto elements.
@@ -47,6 +48,7 @@ func (r *reflector) VisitOneofField(o *OneOfField)   { r.name = "OneOfField" }
 func (r *reflector) VisitReserved(rs *Reserved)      { r.name = "Reserved" }
 func (r *reflector) VisitRPC(rpc *RPC)               { r.name = "RPC" }
 func (r *reflector) VisitMapField(f *MapField)       { r.name = "MapField" }
+func (r *reflector) VisitGroup(g *Group)             { r.name = "Group" }
 
 // nameOfVisitee returns the short type name of a Visitee.
 func nameOfVisitee(e Visitee) string {