Distinguish between empty slice and nil slice

encode.go

@@ -231,7 +231,11 @@ func (e *Encoder) encodeBool(v bool) ast.Node {
 }
 
 func (e *Encoder) encodeSlice(value reflect.Value) (ast.Node, error) {
-	sequence := ast.Sequence(token.New("-", "-", e.pos(e.column)), e.isFlowStyle)
+	isFlowStyle := e.isFlowStyle
+	if value.Len() == 0 && !value.IsNil() {
+		isFlowStyle = true
+	}
+	sequence := ast.Sequence(token.New("-", "-", e.pos(e.column)), isFlowStyle)
 	for i := 0; i < value.Len(); i++ {
 		node, err := e.encodeValue(value.Index(i), e.column)
 		if err != nil {

encode_test.go

@@ -189,7 +189,24 @@ func TestEncoder(t *testing.T) {
 				},
 			},
 		},
-
+		{
+			"a: 1\nb:\n\n",
+			struct {
+				A int
+				B []string
+			}{
+				1, ([]string)(nil),
+			},
+		},
+		{
+			"a: 1\nb: []\n",
+			struct {
+				A int
+				B []string
+			}{
+				1, []string{},
+			},
+		},
 		{
 			"a: b\nc: d\n",
 			struct {
@@ -265,6 +282,15 @@ func TestEncoder(t *testing.T) {
 				B float64 `yaml:"b,omitempty"`
 			}{1, 0},
 		},
+		{
+			"a: 1\n",
+			struct {
+				A int
+				B []string `yaml:"b,omitempty"`
+			}{
+				1, []string{},
+			},
+		},
 
 		// Flow flag
 		{