Slice support.

build.go

@@ -85,6 +85,7 @@ func buildNode(v reflect.Value) *Node {
 				Help:     help,
 				Decoder:  decoder,
 				Value:    fv,
+				Field:    ft,
 				Required: !optional || required,
 			}
 			if arg {

decoders.go

@@ -4,15 +4,23 @@ import (
 	"fmt"
 	"reflect"
 	"strconv"
+	"strings"
 )
 
-type Decoder interface {
+type DecoderContext struct {
-	Decode(scan *Scanner, target reflect.Value) error
+	// Value being decoded into.
+	Value *Value
 }
 
-type DecoderFunc func(scan *Scanner, target reflect.Value) error
+type Decoder interface {
+	Decode(ctx *DecoderContext, scan *Scanner, target reflect.Value) error
+}
 
-func (d DecoderFunc) Decode(scan *Scanner, target reflect.Value) error { return d(scan, target) }
+type DecoderFunc func(ctx *DecoderContext, scan *Scanner, target reflect.Value) error
+
+func (d DecoderFunc) Decode(ctx *DecoderContext, scan *Scanner, target reflect.Value) error {
+	return d(ctx, scan, target)
+}
 
 var _ Decoder = DecoderFunc(nil)
 
@@ -76,6 +84,8 @@ var (
 	kindDecoders  map[reflect.Kind]KindDecoder
 )
 
+// DecoderForField finds a decoder for a struct field.
+//
 func DecoderForField(field reflect.StructField) Decoder {
 	name, ok := field.Tag.Lookup("type")
 	if ok {
@@ -116,7 +126,7 @@ func RegisterDecoder(decoders ...Decoder) {
 }
 
 func init() {
-	intDecoder := NewKindDecoder(reflect.Int, func(scan *Scanner, target reflect.Value) error {
+	intDecoder := NewKindDecoder(reflect.Int, func(ctx *DecoderContext, scan *Scanner, target reflect.Value) error {
 		n, err := strconv.ParseInt(scan.PopValue("int"), 10, 64)
 		if err != nil {
 			return err
@@ -124,7 +134,7 @@ func init() {
 		target.SetInt(n)
 		return nil
 	})
-	uintDecoder := NewKindDecoder(reflect.Uint, func(scan *Scanner, target reflect.Value) error {
+	uintDecoder := NewKindDecoder(reflect.Uint, func(ctx *DecoderContext, scan *Scanner, target reflect.Value) error {
 		n, err := strconv.ParseUint(scan.PopValue("uint"), 10, 64)
 		if err != nil {
 			return err
@@ -143,7 +153,7 @@ func init() {
 		reflect.Uint16: uintDecoder,
 		reflect.Uint32: uintDecoder,
 		reflect.Uint64: uintDecoder,
-		reflect.Float32: NewKindDecoder(reflect.Float32, func(scan *Scanner, target reflect.Value) error {
+		reflect.Float32: NewKindDecoder(reflect.Float32, func(ctx *DecoderContext, scan *Scanner, target reflect.Value) error {
 			n, err := strconv.ParseFloat(scan.PopValue("float"), 32)
 			if err != nil {
 				return err
@@ -151,7 +161,7 @@ func init() {
 			target.SetFloat(n)
 			return nil
 		}),
-		reflect.Float64: NewKindDecoder(reflect.Float64, func(scan *Scanner, target reflect.Value) error {
+		reflect.Float64: NewKindDecoder(reflect.Float64, func(ctx *DecoderContext, scan *Scanner, target reflect.Value) error {
 			n, err := strconv.ParseFloat(scan.PopValue("float"), 64)
 			if err != nil {
 				return err
@@ -159,17 +169,35 @@ func init() {
 			target.SetFloat(n)
 			return nil
 		}),
-		reflect.String: NewKindDecoder(reflect.String, func(scan *Scanner, target reflect.Value) error {
+		reflect.String: NewKindDecoder(reflect.String, func(ctx *DecoderContext, scan *Scanner, target reflect.Value) error {
 			target.SetString(scan.PopValue("string"))
 			return nil
 		}),
-		reflect.Bool: NewKindDecoder(reflect.Bool, func(scan *Scanner, target reflect.Value) error {
+		reflect.Bool: NewKindDecoder(reflect.Bool, func(ctx *DecoderContext, scan *Scanner, target reflect.Value) error {
 			target.SetBool(true)
 			return nil
 		}),
+		reflect.Slice: NewKindDecoder(reflect.Slice, func(ctx *DecoderContext, scan *Scanner, target reflect.Value) error {
+			el := target.Type().Elem()
+			sep, ok := ctx.Value.Field.Tag.Lookup("sep")
+			if !ok {
+				sep = ","
+			}
+			childScanner := Scan(strings.Split(scan.PopValue("slice"), sep)...)
+			childDecoder := DecoderForType(el)
+			for childScanner.Peek().Type != EOLToken {
+				childValue := reflect.New(el).Elem()
+				err := childDecoder.Decode(ctx, childScanner, childValue)
+				if err != nil {
+					return err
+				}
+				target.Set(reflect.Append(target, childValue))
+			}
+			return nil
+		}),
 	}
 }
 
-var missingDecoder DecoderFunc = func(scan *Scanner, target reflect.Value) error {
+var missingDecoder DecoderFunc = func(ctx *DecoderContext, scan *Scanner, target reflect.Value) error {
-	return fmt.Errorf("no decoder for %q (of type %T)", target.String(), target.Type())
+	return fmt.Errorf("no decoder for %q (of type %T) for field %q", target.String(), target.Type(), ctx.Value.Field.Name)
 }

kong.go

@@ -49,10 +49,9 @@ func (k *Kong) Parse(args []string) (command string, err error) {
 // Recursively reset values to defaults (as specified in the grammar) or the zero value.
 func (k *Kong) reset(node *Node) {
 	for _, flag := range node.Flags {
-		if flag.Default != "" {
-			flag.Decoder.Decode(Scan(flag.Default), flag.Value.Value)
-		} else {
 		flag.Value.Value.Set(reflect.Zero(flag.Value.Value.Type()))
+		if flag.Default != "" {
+			flag.Decoder.Decode(&DecoderContext{Value: &flag.Value}, Scan(flag.Default), flag.Value.Value)
 		}
 	}
 	for _, pos := range node.Positional {
@@ -76,35 +75,39 @@ func (k *Kong) applyNode(scan *Scanner, node *Node) (command []string, err error
 			switch {
 			// -- indicates end of parsing. All remaining arguments are treated as positional arguments only.
 			case token.Value == "--":
+				args := []string{}
 				for {
 					token = scan.Pop()
 					if token.Type == EOLToken {
 						break
 					}
-					scan.PushTyped(token.Value, PositionalArgumentToken)
+					args = append(args, token.Value)
+				}
+				for i := range args {
+					scan.PushTyped(args[len(args)-1-i], PositionalArgumentToken)
 				}
 
 			// Long flag.
 			case strings.HasPrefix(token.Value, "--"):
 				// Parse it and push the tokens.
 				parts := strings.SplitN(token.Value[2:], "=", 2)
-				scan.PushTyped(parts[0], FlagToken)
 				if len(parts) > 1 {
 					scan.PushTyped(parts[1], FlagValueToken)
 				}
+				scan.PushTyped(parts[0], FlagToken)
 
 				// Short flag.
 			case strings.HasPrefix(token.Value, "-"):
-				scan.PushTyped(token.Value[1:2], ShortFlagToken)
 				scan.PushTyped(token.Value[2:], ShortFlagTailToken)
+				scan.PushTyped(token.Value[1:2], ShortFlagToken)
 
 			default:
 				scan.PushTyped(token.Value, PositionalArgumentToken)
 			}
 
 		case ShortFlagTailToken:
-			scan.PushTyped(token.Value[0:1], ShortFlagToken)
 			scan.PushTyped(token.Value[1:], ShortFlagTailToken)
+			scan.PushTyped(token.Value[0:1], ShortFlagToken)
 
 		case FlagToken:
 			if err := matchFlags(node.Flags, token, scan, func(f *Flag) bool {
@@ -140,7 +143,7 @@ func (k *Kong) applyNode(scan *Scanner, node *Node) (command []string, err error
 
 				case branch.Argument != nil:
 					arg := branch.Argument.Argument
-					if err := arg.Decoder.Decode(scan, arg.Value); err == nil {
+					if err := arg.Decoder.Decode(&DecoderContext{Value: arg}, scan, arg.Value); err == nil {
 						command = append(command, "<"+arg.Name+">")
 						cmd, err := k.applyNode(scan, &branch.Argument.Node)
 						if err != nil {
@@ -171,7 +174,7 @@ func matchFlags(flags []*Flag, token Token, scan *Scanner, matcher func(f *Flag)
 	for _, flag := range flags {
 		// Found a matching flag.
 		if flag.Name == token.Value {
-			err := flag.Decoder.Decode(scan, flag.Value.Value)
+			err := flag.Decoder.Decode(&DecoderContext{Value: &flag.Value}, scan, flag.Value.Value)
 			if err != nil {
 				return err
 			}

kong_test.go

@@ -1,12 +1,9 @@
 package kong
 
 import (
-	"reflect"
 	"testing"
 
 	"github.com/stretchr/testify/require"
-
-	"github.com/alecthomas/repr"
 )
 
 func mustNew(t *testing.T, cli interface{}) *Kong {
@@ -41,7 +38,6 @@ func TestArgument(t *testing.T) {
 		} `arg:"true"`
 	}
 	p := mustNew(t, &cli)
-	repr.Println(p.Model, repr.Hide(reflect.Value{}))
 	cmd, err := p.Parse([]string{"10", "delete"})
 	require.NoError(t, err)
 	require.Equal(t, 10, cli.Id.Id)
@@ -61,3 +57,13 @@ func TestResetWithDefaults(t *testing.T) {
 	require.Equal(t, "", cli.Flag)
 	require.Equal(t, "default", cli.FlagWithDefault)
 }
+
+func TestSlice(t *testing.T) {
+	var cli struct {
+		Slice []int
+	}
+	parser := mustNew(t, &cli)
+	_, err := parser.Parse([]string{"--slice=1,2,3"})
+	require.NoError(t, err)
+	require.Equal(t, []int{1, 2, 3}, cli.Slice)
+}

model.go

@@ -24,6 +24,7 @@ type Value struct {
 	Name     string
 	Help     string
 	Decoder  Decoder
+	Field    reflect.StructField
 	Value    reflect.Value
 	Required bool
 }

scanner.go

@@ -60,18 +60,21 @@ func (t Token) IsValue() bool {
 }
 
 type Scanner struct {
-	raw  []string
 	args []Token
 }
 
 func Scan(args ...string) *Scanner {
-	s := &Scanner{raw: args}
+	s := &Scanner{}
 	for _, arg := range args {
 		s.args = append(s.args, Token{Value: arg})
 	}
 	return s
 }
 
+func (s *Scanner) Len() int {
+	return len(s.args)
+}
+
 func (s *Scanner) Pop() Token {
 	if len(s.args) == 0 {
 		return Token{Type: EOLToken}