Allow DynamicCommand to specify arbitrary tags.

Fixes #185.

README.md

@@ -25,6 +25,7 @@
 - [Custom decoders mappers](#custom-decoders-mappers)
 - [Supported tags](#supported-tags)
 - [Plugins](#plugins)
+- [Dynamic Commands](#dynamic-commands)
 - [Variable interpolation](#variable-interpolation)
 - [Validation](#validation)
 - [Modifying Kong's behaviour](#modifying-kongs-behaviour)
@@ -474,6 +475,11 @@ cli.Plugins = kong.Plugins{&pluginOne, &pluginTwo}
 
 Additionally if an interface type is embedded, it can also be populated with a Kong annotated struct.
 
+## Dynamic Commands
+
+While plugins give complete control over extending command-line interfaces, Kong
+also supports dynamically adding commands via `kong.DynamicCommand()`.
+
 ## Variable interpolation
 
 Kong supports limited variable interpolation into help strings, enum lists and

build.go

@@ -51,7 +51,7 @@ 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(v, fv, ft)
+		tag := parseTag(v, ft)
 		if tag.Ignored {
 			continue
 		}

kong.go

@@ -118,7 +118,7 @@ func New(grammar interface{}, options ...Option) (*Kong, error) {
 
 	// Synthesise command nodes.
 	for _, dcmd := range k.dynamicCommands {
-		tag := newEmptyTag()
+		tag := parseTagString(strings.Join(dcmd.tags, " "))
 		tag.Name = dcmd.name
 		tag.Help = dcmd.help
 		tag.Group = dcmd.group

kong_test.go

@@ -1242,9 +1242,14 @@ func TestDynamicCommands(t *testing.T) {
 	cli := struct {
 		One struct{} `cmd:"one"`
 	}{}
+	help := &strings.Builder{}
 	two := &dynamicCommand{}
-	var twoi interface{} = &two
-	p := mustNew(t, &cli, kong.DynamicCommand("two", "", "", twoi))
+	three := &dynamicCommand{}
+	p := mustNew(t, &cli,
+		kong.DynamicCommand("two", "", "", &two),
+		kong.DynamicCommand("three", "", "", three, "hidden"),
+		kong.Writers(help, help),
+		kong.Exit(func(int) {}))
 	kctx, err := p.Parse([]string{"two", "--flag=flag"})
 	require.NoError(t, err)
 	require.Equal(t, "flag", two.Flag)
@@ -1252,6 +1257,10 @@ func TestDynamicCommands(t *testing.T) {
 	err = kctx.Run()
 	require.NoError(t, err)
 	require.True(t, two.ran)
+
+	_, err = p.Parse([]string{"--help"})
+	require.EqualError(t, err, `expected one of "one",  "two"`)
+	require.NotContains(t, help.String(), "three", help.String())
 }
 
 func TestDuplicateShortflags(t *testing.T) {

options.go

@@ -58,19 +58,23 @@ type dynamicCommand struct {
 	name  string
 	help  string
 	group string
+	tags  []string
 	cmd   interface{}
 }
 
 // DynamicCommand registers a dynamically constructed command with the root of the CLI.
 //
 // This is useful for command-line structures that are extensible via user-provided plugins.
-func DynamicCommand(name, help, group string, cmd interface{}) Option {
+//
+// "tags" is a list of extra tag strings to parse, in the form <key>:"<value>".
+func DynamicCommand(name, help, group string, cmd interface{}, tags ...string) Option {
 	return OptionFunc(func(k *Kong) error {
 		k.dynamicCommands = append(k.dynamicCommands, &dynamicCommand{
 			name:  name,
 			help:  help,
 			group: group,
 			cmd:   cmd,
+			tags:  tags,
 		})
 		return nil
 	})

tag.go

@@ -129,24 +129,41 @@ func tagSplitFn(r rune) bool {
 	return r == ',' || r == ' '
 }
 
-func parseTag(parent, fv reflect.Value, ft reflect.StructField) *Tag {
+func parseTagString(s string) *Tag {
+	t := &Tag{
+		items: parseTagItems(s, bareChars),
+	}
+	err := hydrateTag(t, "", false)
+	if err != nil {
+		fail("%s: %s", s, err)
+	}
+	return t
+}
+
+func parseTag(parent reflect.Value, ft reflect.StructField) *Tag {
 	if ft.Tag.Get("kong") == "-" {
 		t := newEmptyTag()
 		t.Ignored = true
 		return t
 	}
-	var (
-		err error
-		t   = &Tag{
-			items: parseTagItems(getTagInfo(ft)),
-		}
-	)
+	t := &Tag{
+		items: parseTagItems(getTagInfo(ft)),
+	}
+	err := hydrateTag(t, ft.Type.Name(), ft.Type.Kind() == reflect.Bool)
+	if err != nil {
+		failField(parent, ft, "%s", err)
+	}
+	return t
+}
+
+func hydrateTag(t *Tag, typeName string, isBool bool) error {
+	var err error
 	t.Cmd = t.Has("cmd")
 	t.Arg = t.Has("arg")
 	required := t.Has("required")
 	optional := t.Has("optional")
 	if required && optional {
-		failField(parent, ft, "can't specify both required and optional")
+		return fmt.Errorf("can't specify both required and optional")
 	}
 	t.Required = required
 	t.Optional = optional
@@ -161,7 +178,7 @@ func parseTag(parent, fv reflect.Value, ft reflect.StructField) *Tag {
 	t.Env = t.Get("env")
 	t.Short, err = t.GetRune("short")
 	if err != nil && t.Get("short") != "" {
-		failField(parent, ft, "invalid short flag name %q: %s", t.Get("short"), err)
+		return fmt.Errorf("invalid short flag name %q: %s", t.Get("short"), err)
 	}
 	t.Hidden = t.Has("hidden")
 	t.Format = t.Get("format")
@@ -174,8 +191,8 @@ func parseTag(parent, fv reflect.Value, ft reflect.StructField) *Tag {
 	t.Prefix = t.Get("prefix")
 	t.Embed = t.Has("embed")
 	negatable := t.Has("negatable")
-	if negatable && ft.Type.Kind() != reflect.Bool {
-		failField(parent, ft, "negatable can only be set on booleans")
+	if negatable && !isBool {
+		return fmt.Errorf("negatable can only be set on booleans")
 	}
 	t.Negatable = negatable
 	aliases := t.Get("aliases")
@@ -186,24 +203,24 @@ func parseTag(parent, fv reflect.Value, ft reflect.StructField) *Tag {
 	for _, set := range t.GetAll("set") {
 		parts := strings.SplitN(set, "=", 2)
 		if len(parts) == 0 {
-			failField(parent, ft, "set should be in the form key=value but got %q", set)
+			return fmt.Errorf("set should be in the form key=value but got %q", set)
 		}
 		t.Vars[parts[0]] = parts[1]
 	}
 	t.PlaceHolder = t.Get("placeholder")
 	if t.PlaceHolder == "" {
-		t.PlaceHolder = strings.ToUpper(dashedString(fv.Type().Name()))
+		t.PlaceHolder = strings.ToUpper(dashedString(typeName))
 	}
 	t.Enum = t.Get("enum")
 	if t.Enum != "" && !(t.Required || t.Default != "") {
-		failField(parent, ft, "enum value is only valid if it is either required or has a valid default value")
+		return fmt.Errorf("enum value is only valid if it is either required or has a valid default value")
 	}
 	passthrough := t.Has("passthrough")
 	if passthrough && !t.Arg {
-		failField(parent, ft, "passthrough only makes sense for positional arguments")
+		return fmt.Errorf("passthrough only makes sense for positional arguments")
 	}
 	t.Passthrough = passthrough
-	return t
+	return nil
 }
 
 // Has returns true if the tag contained the given key.