Better printing of newlines, some round-tripping support

cmd/toml-test-decoder/main.go

@@ -31,13 +31,14 @@ func main() {
 	}
 
 	var decoded interface{}
-	if _, err := toml.DecodeReader(os.Stdin, &decoded); err != nil {
+	meta, err := toml.DecodeReader(os.Stdin, &decoded)
+	if err != nil {
 		log.Fatalf("Error decoding TOML: %s", err)
 	}
 
 	j := json.NewEncoder(os.Stdout)
 	j.SetIndent("", "  ")
-	if err := j.Encode(tag.Add("", decoded)); err != nil {
+	if err := j.Encode(tag.Add(meta, "", decoded)); err != nil {
 		log.Fatalf("Error encoding JSON: %s", err)
 	}
 }

decode.go

@@ -111,11 +111,12 @@ func (dec *Decoder) Decode(v interface{}) (MetaData, error) {
 		return MetaData{}, err
 	}
 	md := MetaData{
-		mapping: p.mapping,
-		types:   p.types,
-		keys:    p.ordered,
-		decoded: make(map[string]bool, len(p.ordered)),
-		context: nil,
+		mapping:  p.mapping,
+		types:    p.types,
+		keys:     p.ordered,
+		comments: p.comments,
+		decoded:  make(map[string]bool, len(p.ordered)),
+		context:  nil,
 	}
 	return md, md.unify(p.mapping, indirect(rv))
 }
@@ -244,17 +245,17 @@ func (md *MetaData) unifyStruct(mapping interface{}, rv reflect.Value) error {
 			for _, i := range f.index {
 				subv = indirect(subv.Field(i))
 			}
+
 			if isUnifiable(subv) {
 				md.decoded[md.context.add(key).String()] = true
 				md.context = append(md.context, key)
-				if err := md.unify(datum, subv); err != nil {
+				err := md.unify(datum, subv)
+				if err != nil {
 					return err
 				}
 				md.context = md.context[0 : len(md.context)-1]
 			} else if f.name != "" {
-				// Bad user! No soup for you!
-				return e("cannot write unexported field %s.%s",
-					rv.Type().String(), f.name)
+				return e("cannot write unexported field %s.%s", rv.Type().String(), f.name)
 			}
 		}
 	}
@@ -445,6 +446,7 @@ func (md *MetaData) unifyText(data interface{}, v encoding.TextUnmarshaler) erro
 	var s string
 	switch sdata := data.(type) {
 	case Marshaler:
+		fmt.Println("unifyText (Marshaler)", data, "in to", v)
 		text, err := sdata.MarshalTOML()
 		if err != nil {
 			return err
@@ -456,6 +458,7 @@ func (md *MetaData) unifyText(data interface{}, v encoding.TextUnmarshaler) erro
 			return err
 		}
 		s = string(text)
+		// fmt.Println("unifyText (TextMarshaler)", data, "in to", v, "=", s)
 	case fmt.Stringer:
 		s = sdata.String()
 	case string: