Support for flag prefixing.

README.md

@@ -395,7 +395,9 @@ Both can coexist with standard Tag parsing.
 | `hidden`               | If present, command or flag is hidden.      |
 | `format:"X"`           | Format for parsing input, if supported.     |
 | `sep:"X"`              | Separator for sequences (defaults to ","). May be `none` to disable splitting. |
-| `enum:"X,Y,..."`       |
+| `enum:"X,Y,..."`       | Set of valid values allowed for this flag.  |
+| `group:"X"`            | Logical group for a flag or command.        |
+| `prefix:"X"`           | Prefix for all sub-flags.                   |
 
 ## Variable interpolation
 

build.go

@@ -38,20 +38,30 @@ func dashedString(s string) string {
 type flattenedField struct {
 	field reflect.StructField
 	value reflect.Value
+	tag   *Tag
 }
 
 func flattenedFields(v reflect.Value) (out []flattenedField) {
 	for i := 0; i < v.NumField(); i++ {
 		ft := v.Type().Field(i)
 		fv := v.Field(i)
+		tag := parseTag(fv, ft)
 		if ft.Anonymous {
-			out = append(out, flattenedFields(fv)...)
+			sub := flattenedFields(fv)
+			// Assign parent group to children, if they're not otherwise set.
+			for _, subf := range sub {
+				if subf.tag.Group == "" {
+					subf.tag.Group = tag.Group
+				}
+				subf.tag.Prefix = tag.Prefix + subf.tag.Prefix
+			}
+			out = append(out, sub...)
 			continue
 		}
 		if !fv.CanSet() {
 			continue
 		}
-		out = append(out, flattenedField{field: ft, value: fv})
+		out = append(out, flattenedField{field: ft, value: fv, tag: tag})
 	}
 	return
 }
@@ -65,11 +75,12 @@ func buildNode(k *Kong, v reflect.Value, typ NodeType, seenFlags map[string]bool
 		ft := field.field
 		fv := field.value
 
-		tag := parseTag(fv, ft)
+		tag := field.tag
-
 		name := tag.Name
 		if name == "" {
-			name = strings.ToLower(dashedString(ft.Name))
+			name = tag.Prefix + strings.ToLower(dashedString(ft.Name))
+		} else {
+			name = tag.Prefix + name
 		}
 
 		// Nested structs are either commands or args, unless they implement the Mapper interface.
@@ -108,6 +119,7 @@ func buildChild(k *Kong, node *Node, typ NodeType, v reflect.Value, ft reflect.S
 	child.Parent = node
 	child.Help = tag.Help
 	child.Hidden = tag.Hidden
+	child.Group = tag.Group
 
 	if fv.Type().Implements(helpProviderType) {
 		child.Detail = fv.Interface().(HelpProvider).Help()
@@ -176,6 +188,7 @@ func buildField(k *Kong, node *Node, v reflect.Value, ft reflect.StructField, fv
 			Short:       tag.Short,
 			PlaceHolder: tag.PlaceHolder,
 			Env:         tag.Env,
+			Group:       tag.Group,
 		}
 		value.Flag = flag
 		node.Flags = append(node.Flags, flag)

kong_test.go

@@ -577,3 +577,16 @@ func TestBoolOverride(t *testing.T) {
 	_, err = p.Parse([]string{"--flag", "false"})
 	require.Error(t, err)
 }
+
+func TestAnonymousPrefix(t *testing.T) {
+	type Anonymous struct {
+		Flag string
+	}
+	var cli struct {
+		Anonymous `prefix:"anon-"`
+	}
+	p := mustNew(t, &cli)
+	_, err := p.Parse([]string{"--anon-flag=moo"})
+	require.NoError(t, err)
+	require.Equal(t, "moo", cli.Flag)
+}

model.go

@@ -37,6 +37,7 @@ type Node struct {
 	Name       string
 	Help       string // Short help displayed in summaries.
 	Detail     string // Detailed help displayed when describing command/arg alone.
+	Group      string
 	Hidden     bool
 	Flags      []*Flag
 	Positional []*Positional
@@ -284,6 +285,7 @@ type Positional = Value
 // A Flag represents a command-line flag.
 type Flag struct {
 	*Value
+	Group       string // Logical grouping when displaying. May also be used by configuration loaders to group options logically.
 	PlaceHolder string
 	Env         string
 	Short       rune

tag.go

@@ -25,6 +25,8 @@ type Tag struct {
 	Hidden      bool
 	Sep         rune
 	Enum        string
+	Group       string
+	Prefix      string // Optional prefix on anonymous structs. All sub-flags will have this prefix.
 
 	// Storage for all tag keys for arbitrary lookups.
 	items map[string]string
@@ -137,6 +139,8 @@ func parseTag(fv reflect.Value, ft reflect.StructField) *Tag {
 	t.Hidden = t.Has("hidden")
 	t.Format = t.Get("format")
 	t.Sep, _ = t.GetRune("sep")
+	t.Group = t.Get("group")
+	t.Prefix = t.Get("prefix")
 	if t.Sep == 0 {
 		if t.Get("sep") == "none" {
 			t.Sep = -1