Matching arg field (#1)

Check if the first field of an argument branch matches the parent struct field.

build.go

@@ -79,6 +79,10 @@ func buildNode(v reflect.Value, cmd bool) *Node {
 					child.Help = value.Help
 				}
 				child.Name = value.Name
+				if child.Name != name {
+					fail("first field in positional branch %s.%s must have the same name as the parent field (%s).",
+						v.Type().Name(), ft.Name, child.Name)
+				}
 				node.Children = append(node.Children, &Branch{Argument: &Argument{
 					Node:     *child,
 					Argument: value,

kong_test.go

@@ -98,10 +98,21 @@ func TestArgSlice(t *testing.T) {
 	require.Equal(t, true, cli.Flag)
 }
 
-func TestUnsupportedfieldErrors(t *testing.T) {
+func TestUnsupportedFieldErrors(t *testing.T) {
 	var cli struct {
 		Keys map[string]string
 	}
 	_, err := New("", "", &cli)
 	require.Error(t, err)
 }
+
+func TestMatchingArgField(t *testing.T) {
+	var cli struct {
+		ID struct {
+			NotID int `arg:""`
+		} `arg:""`
+	}
+
+	_, err := New("", "", &cli)
+	require.Error(t, err)
+}