Allow multiple xor:"" groups to be defined.

Fixes #113.

README.md

@@ -446,7 +446,7 @@ Tag                    | Description
 `mapsep:"X"`           | Separator for maps (defaults to ";"). May be `none` to disable splitting.
 `enum:"X,Y,..."`       | Set of valid values allowed for this flag.
 `group:"X"`            | Logical group for a flag or command.
-`xor:"X"`              | Exclusive OR group for flags. Only one flag in the group can be used which is restricted within the same command.
+`xor:"X,Y,..."`        | Exclusive OR groups for flags. Only one flag in the group can be used which is restricted within the same command.
 `prefix:"X"`           | Prefix for all sub-flags.
 `set:"K=V"`            | Set a variable for expansion by child elements. Multiples can occur.
 `embed:""`             | If present, this field's children will be embedded in the parent. Useful for composition.

context.go

@@ -871,13 +871,12 @@ func checkXorDuplicates(paths []*Path) error {
 			if !flag.Set {
 				continue
 			}
-			if flag.Xor == "" {
-				continue
+			for _, xor := range flag.Xor {
+				if seen[xor] != nil {
+					return fmt.Errorf("--%s and --%s can't be used together", seen[xor].Name, flag.Name)
+				}
+				seen[xor] = flag
 			}
-			if seen[flag.Xor] != nil {
-				return fmt.Errorf("--%s and --%s can't be used together", seen[flag.Xor].Name, flag.Name)
-			}
-			seen[flag.Xor] = flag
 		}
 	}
 	return nil

kong_test.go

@@ -868,6 +868,22 @@ func TestXorChild(t *testing.T) {
 	require.Error(t, err, "--two and --three can't be used together")
 }
 
+func TestMultiXor(t *testing.T) {
+	var cli struct {
+		Hello bool   `xor:"one,two"`
+		One   bool   `xor:"one"`
+		Two   string `xor:"two"`
+	}
+
+	p := mustNew(t, &cli)
+	_, err := p.Parse([]string{"--hello", "--one"})
+	require.EqualError(t, err, "--hello and --one can't be used together")
+
+	p = mustNew(t, &cli)
+	_, err = p.Parse([]string{"--hello", "--two=foo"})
+	require.EqualError(t, err, "--hello and --two can't be used together")
+}
+
 func TestEnumSequence(t *testing.T) {
 	var cli struct {
 		State []string `enum:"a,b,c" default:"a"`

model.go

@@ -377,7 +377,7 @@ type Positional = Value
 type Flag struct {
 	*Value
 	Group       *Group // Logical grouping when displaying. May also be used by configuration loaders to group options logically.
-	Xor         string
+	Xor         []string
 	PlaceHolder string
 	Env         string
 	Short       rune

tag.go

@@ -29,7 +29,7 @@ type Tag struct {
 	MapSep      rune
 	Enum        string
 	Group       string
-	Xor         string
+	Xor         []string
 	Vars        Vars
 	Prefix      string // Optional prefix on anonymous structs. All sub-flags will have this prefix.
 	Embed       bool
@@ -125,6 +125,10 @@ func newEmptyTag() *Tag {
 	return &Tag{items: map[string][]string{}}
 }
 
+func tagSplitFn(r rune) bool {
+	return r == ',' || r == ' '
+}
+
 func parseTag(fv reflect.Value, ft reflect.StructField) *Tag {
 	if ft.Tag.Get("kong") == "-" {
 		t := newEmptyTag()
@@ -164,7 +168,9 @@ func parseTag(fv reflect.Value, ft reflect.StructField) *Tag {
 	t.Sep, _ = t.GetSep("sep", ',')
 	t.MapSep, _ = t.GetSep("mapsep", ';')
 	t.Group = t.Get("group")
-	t.Xor = t.Get("xor")
+	for _, xor := range t.GetAll("xor") {
+		t.Xor = append(t.Xor, strings.FieldsFunc(xor, tagSplitFn)...)
+	}
 	t.Prefix = t.Get("prefix")
 	t.Embed = t.Has("embed")
 	negatable := t.Has("negatable")
@@ -172,12 +178,9 @@ func parseTag(fv reflect.Value, ft reflect.StructField) *Tag {
 		fail("negatable can only be set on booleans")
 	}
 	t.Negatable = negatable
-	splitFn := func(r rune) bool {
-		return r == ',' || r == ' '
-	}
 	aliases := t.Get("aliases")
 	if len(aliases) > 0 {
-		t.Aliases = append(t.Aliases, strings.FieldsFunc(aliases, splitFn)...)
+		t.Aliases = append(t.Aliases, strings.FieldsFunc(aliases, tagSplitFn)...)
 	}
 	t.Vars = Vars{}
 	for _, set := range t.GetAll("set") {