Multiline Marshal tag (#221)

The new multiline tag works just like the existing 'commented' tag (i.e.
`multiline:"true"`), and tells go-toml to marshal the value as a
multi-line string. The tag currently has no impact on any non-string
fields.

marshal.go

@@ -11,10 +11,13 @@ import (
 	"time"
 )
 
+const tagKeyMultiline = "multiline"
+
 type tomlOpts struct {
 	name      string
 	comment   string
 	commented bool
+	multiline bool
 	include   bool
 	omitempty bool
 }
@@ -230,7 +233,12 @@ func (e *Encoder) valueToTree(mtype reflect.Type, mval reflect.Value) (*Tree, er
 				if err != nil {
 					return nil, err
 				}
-				tval.SetWithComment(opts.name, opts.comment, opts.commented, val)
+
+				tval.SetWithOptions(opts.name, SetOptions{
+					Comment:   opts.comment,
+					Commented: opts.commented,
+					Multiline: opts.multiline,
+				}, val)
 			}
 		}
 	case reflect.Map:
@@ -559,7 +567,8 @@ func tomlOptions(vf reflect.StructField) tomlOpts {
 		comment = c
 	}
 	commented, _ := strconv.ParseBool(vf.Tag.Get("commented"))
-	result := tomlOpts{name: vf.Name, comment: comment, commented: commented, include: true, omitempty: false}
+	multiline, _ := strconv.ParseBool(vf.Tag.Get(tagKeyMultiline))
+	result := tomlOpts{name: vf.Name, comment: comment, commented: commented, multiline: multiline, include: true, omitempty: false}
 	if parse[0] != "" {
 		if parse[0] == "-" && len(parse) == 1 {
 			result.include = false

toml.go

@@ -14,6 +14,7 @@ type tomlValue struct {
 	value     interface{} // string, int64, uint64, float64, bool, time.Time, [] of any of this list
 	comment   string
 	commented bool
+	multiline bool
 	position  Position
 }
 
@@ -175,6 +176,63 @@ func (t *Tree) GetDefault(key string, def interface{}) interface{} {
 	return val
 }
 
+// SetOptions arguments are supplied to the SetWithOptions and SetPathWithOptions functions to modify marshalling behaviour.
+// The default values within the struct are valid default options.
+type SetOptions struct {
+	Comment   string
+	Commented bool
+	Multiline bool
+}
+
+// SetWithOptions is the same as Set, but allows you to provide formatting
+// instructions to the key, that will be used by Marshal().
+func (t *Tree) SetWithOptions(key string, opts SetOptions, value interface{}) {
+	t.SetPathWithOptions(strings.Split(key, "."), opts, value)
+}
+
+// SetPathWithOptions is the same as SetPath, but allows you to provide
+// formatting instructions to the key, that will be reused by Marshal().
+func (t *Tree) SetPathWithOptions(keys []string, opts SetOptions, value interface{}) {
+	subtree := t
+	for _, intermediateKey := range keys[:len(keys)-1] {
+		nextTree, exists := subtree.values[intermediateKey]
+		if !exists {
+			nextTree = newTree()
+			subtree.values[intermediateKey] = nextTree // add new element here
+		}
+		switch node := nextTree.(type) {
+		case *Tree:
+			subtree = node
+		case []*Tree:
+			// go to most recent element
+			if len(node) == 0 {
+				// create element if it does not exist
+				subtree.values[intermediateKey] = append(node, newTree())
+			}
+			subtree = node[len(node)-1]
+		}
+	}
+
+	var toInsert interface{}
+
+	switch value.(type) {
+	case *Tree:
+		tt := value.(*Tree)
+		tt.comment = opts.Comment
+		toInsert = value
+	case []*Tree:
+		toInsert = value
+	case *tomlValue:
+		tt := value.(*tomlValue)
+		tt.comment = opts.Comment
+		toInsert = tt
+	default:
+		toInsert = &tomlValue{value: value, comment: opts.Comment, commented: opts.Commented, multiline: opts.Multiline}
+	}
+
+	subtree.values[keys[len(keys)-1]] = toInsert
+}
+
 // Set an element in the tree.
 // Key is a dot-separated path (e.g. a.b.c).
 // Creates all necessary intermediate trees, if needed.

tomltree_write.go

@@ -12,7 +12,41 @@ import (
 	"time"
 )
 
-// encodes a string to a TOML-compliant string value
+// Encodes a string to a TOML-compliant multi-line string value
+// This function is a clone of the existing encodeTomlString function, except that whitespace characters
+// are preserved. Quotation marks and backslashes are also not escaped.
+func encodeMultilineTomlString(value string) string {
+	var b bytes.Buffer
+
+	for _, rr := range value {
+		switch rr {
+		case '\b':
+			b.WriteString(`\b`)
+		case '\t':
+			b.WriteString("\t")
+		case '\n':
+			b.WriteString("\n")
+		case '\f':
+			b.WriteString(`\f`)
+		case '\r':
+			b.WriteString("\r")
+		case '"':
+			b.WriteString(`"`)
+		case '\\':
+			b.WriteString(`\`)
+		default:
+			intRr := uint16(rr)
+			if intRr < 0x001F {
+				b.WriteString(fmt.Sprintf("\\u%0.4X", intRr))
+			} else {
+				b.WriteRune(rr)
+			}
+		}
+	}
+	return b.String()
+}
+
+// Encodes a string to a TOML-compliant string value
 func encodeTomlString(value string) string {
 	var b bytes.Buffer
 
@@ -45,6 +79,15 @@ func encodeTomlString(value string) string {
 }
 
 func tomlValueStringRepresentation(v interface{}, indent string, arraysOneElementPerLine bool) (string, error) {
+	// this interface check is added to dereference the change made in the writeTo function.
+	// That change was made to allow this function to see formatting options.
+	tv, ok := v.(*tomlValue)
+	if ok {
+		v = tv.value
+	} else {
+		tv = &tomlValue{}
+	}
+
 	switch value := v.(type) {
 	case uint64:
 		return strconv.FormatUint(value, 10), nil
@@ -58,6 +101,9 @@ func tomlValueStringRepresentation(v interface{}, indent string, arraysOneElemen
 		}
 		return strings.ToLower(strconv.FormatFloat(value, 'f', -1, 32)), nil
 	case string:
+		if tv.multiline {
+			return "\"\"\"\n" + encodeMultilineTomlString(value) + "\"\"\"", nil
+		}
 		return "\"" + encodeTomlString(value) + "\"", nil
 	case []byte:
 		b, _ := v.([]byte)
@@ -130,7 +176,7 @@ func (t *Tree) writeTo(w io.Writer, indent, keyspace string, bytesCount int64, a
 			return bytesCount, fmt.Errorf("invalid value type at %s: %T", k, t.values[k])
 		}
 
-		repr, err := tomlValueStringRepresentation(v.value, indent, arraysOneElementPerLine)
+		repr, err := tomlValueStringRepresentation(v, indent, arraysOneElementPerLine)
 		if err != nil {
 			return bytesCount, err
 		}