Support literal multiline marshal (#485)

Use struct tag `multiline:"true" literal:"true"` to enable it.

marshal.go

@@ -18,6 +18,7 @@ const (
 	tagFieldComment = "comment"
 	tagCommented    = "commented"
 	tagMultiline    = "multiline"
+	tagLiteral      = "literal"
 	tagDefault      = "default"
 )
 
@@ -27,6 +28,7 @@ type tomlOpts struct {
 	comment      string
 	commented    bool
 	multiline    bool
+	literal      bool
 	include      bool
 	omitempty    bool
 	defaultValue string
@@ -46,6 +48,7 @@ type annotation struct {
 	comment      string
 	commented    string
 	multiline    string
+	literal      string
 	defaultValue string
 }
 
@@ -54,6 +57,7 @@ var annotationDefault = annotation{
 	comment:      tagFieldComment,
 	commented:    tagCommented,
 	multiline:    tagMultiline,
+	literal:      tagLiteral,
 	defaultValue: tagDefault,
 }
 
@@ -442,6 +446,7 @@ func (e *Encoder) valueToTree(mtype reflect.Type, mval reflect.Value) (*Tree, er
 							Comment:   opts.comment,
 							Commented: opts.commented,
 							Multiline: opts.multiline,
+							Literal:   opts.literal,
 						}, val)
 					}
 				}
@@ -1168,13 +1173,15 @@ func tomlOptions(vf reflect.StructField, an annotation) tomlOpts {
 	}
 	commented, _ := strconv.ParseBool(vf.Tag.Get(an.commented))
 	multiline, _ := strconv.ParseBool(vf.Tag.Get(an.multiline))
+	literal, _ := strconv.ParseBool(vf.Tag.Get(an.literal))
 	defaultValue := vf.Tag.Get(tagDefault)
 	result := tomlOpts{
 		name:         vf.Name,
 		nameFromTag:  false,
 		comment:      comment,
 		commented:    commented,
 		multiline:    multiline,
+		literal:      literal,
 		include:      true,
 		omitempty:    false,
 		defaultValue: defaultValue,

marshal_test.go

@@ -1294,6 +1294,32 @@ NonCommented = "Not commented line"
 	}
 }
 
+func TestMarshalMultilineLiteral(t *testing.T) {
+	type Doc struct {
+		Value string `multiline:"true" literal:"true"`
+	}
+
+	d := Doc{
+		Value: "hello\nworld\ttest\nend",
+	}
+
+	expected := []byte(`Value = '''
+hello
+world	test
+end
+'''
+`)
+
+	b, err := Marshal(d)
+	if err != nil {
+		t.Fatal("unexpected error")
+	}
+
+	if !bytes.Equal(b, expected) {
+		t.Errorf("Bad marshal: expected\n-----\n%s\n-----\ngot\n-----\n%s\n-----\n", expected, b)
+	}
+}
+
 func TestMarshalNonPrimitiveTypeCommented(t *testing.T) {
 	expectedToml := []byte(`
 # [CommentedMapField]

toml.go

@@ -15,6 +15,7 @@ type tomlValue struct {
 	comment   string
 	commented bool
 	multiline bool
+	literal   bool
 	position  Position
 }
 
@@ -314,6 +315,7 @@ type SetOptions struct {
 	Comment   string
 	Commented bool
 	Multiline bool
+	Literal   bool
 }
 
 // SetWithOptions is the same as Set, but allows you to provide formatting
@@ -362,12 +364,14 @@ func (t *Tree) SetPathWithOptions(keys []string, opts SetOptions, value interfac
 		v.comment = opts.Comment
 		v.commented = opts.Commented
 		v.multiline = opts.Multiline
+		v.literal = opts.Literal
 		toInsert = v
 	default:
 		toInsert = &tomlValue{value: value,
 			comment:   opts.Comment,
 			commented: opts.Commented,
 			multiline: opts.Multiline,
+			literal:   opts.Literal,
 			position:  Position{Line: subtree.position.Line + len(subtree.values) + 1, Col: subtree.position.Col}}
 	}
 

tomltree_write.go

@@ -158,7 +158,15 @@ func tomlValueStringRepresentation(v interface{}, commented string, indent strin
 		return strings.ToLower(strconv.FormatFloat(value, 'f', -1, bits)), nil
 	case string:
 		if tv.multiline {
-			return "\"\"\"\n" + encodeMultilineTomlString(value, commented) + "\"\"\"", nil
+			if tv.literal {
+				b := strings.Builder{}
+				b.WriteString("'''\n")
+				b.Write([]byte(value))
+				b.WriteString("\n'''")
+				return b.String(), nil
+			} else {
+				return "\"\"\"\n" + encodeMultilineTomlString(value, commented) + "\"\"\"", nil
+			}
 		}
 		return "\"" + encodeTomlString(value) + "\"", nil
 	case []byte: