Don't panic with 'omitempty' and uncomparable type

encode.go

@@ -653,6 +653,11 @@ func isEmpty(rv reflect.Value) bool {
 	case reflect.Array, reflect.Slice, reflect.Map, reflect.String:
 		return rv.Len() == 0
 	case reflect.Struct:
+		// TODO: should probably return an error here, or do this check
+		//       somewhere else.
+		if !rv.Type().Comparable() {
+			return false
+		}
 		return reflect.Zero(rv.Type()).Interface() == rv.Interface()
 	case reflect.Bool:
 		return !rv.Bool()

encode_test.go

@@ -212,6 +212,24 @@ time = 1985-06-18T15:16:17Z
 		v, expected, nil)
 }
 
+func TestEncodeWithOmitEmptyUncomparable(t *testing.T) {
+	type nest struct {
+		Field []string `toml:"Field,omitempty"`
+	}
+	s := struct {
+		Values nest `toml:"values,omitempty"`
+		Empty  nest `toml:"empty,omitempty"`
+	}{Values: nest{[]string{"XXX"}}}
+
+	buf := new(bytes.Buffer)
+	err := NewEncoder(buf).Encode(s)
+	// if !errorContains(err, "comparing uncomparable type struct") {
+	// 	t.Fatalf("wrong error: %v", err)
+	// }
+	fmt.Println(err)
+	fmt.Println(buf.String())
+}
+
 func TestEncodeWithOmitZero(t *testing.T) {
 	type simple struct {
 		Number   int     `toml:"number,omitzero"`