Bubble errors instead of panicking (#194)

kong.go

@@ -13,22 +13,12 @@ var (
 	callbackReturnSignature = reflect.TypeOf((*error)(nil)).Elem()
 )
 
-// Error reported by Kong.
-type Error struct{ msg string }
-
-func (e Error) Error() string { return e.msg }
-
-func fail(format string, args ...interface{}) {
-	panic(Error{msg: fmt.Sprintf(format, args...)})
-}
-
-func failField(parent reflect.Value, field reflect.StructField, format string, args ...interface{}) {
+func failField(parent reflect.Value, field reflect.StructField, format string, args ...interface{}) error {
 	name := parent.Type().Name()
 	if name == "" {
 		name = "<anonymous struct>"
 	}
-	msg := fmt.Sprintf("%s.%s: %s", name, field.Name, fmt.Sprintf(format, args...))
-	panic(Error{msg: msg})
+	return fmt.Errorf("%s.%s: %s", name, field.Name, fmt.Sprintf(format, args...))
 }
 
 // Must creates a new Parser or panics if there is an error.
@@ -118,16 +108,22 @@ func New(grammar interface{}, options ...Option) (*Kong, error) {
 
 	// Synthesise command nodes.
 	for _, dcmd := range k.dynamicCommands {
-		tag := parseTagString(strings.Join(dcmd.tags, " "))
+		tag, terr := parseTagString(strings.Join(dcmd.tags, " "))
+		if terr != nil {
+			return nil, terr
+		}
 		tag.Name = dcmd.name
 		tag.Help = dcmd.help
 		tag.Group = dcmd.group
 		tag.Cmd = true
 		v := reflect.Indirect(reflect.ValueOf(dcmd.cmd))
-		buildChild(k, k.Model.Node, CommandNode, reflect.Value{}, reflect.StructField{
+		err = buildChild(k, k.Model.Node, CommandNode, reflect.Value{}, reflect.StructField{
 			Name: dcmd.name,
 			Type: v.Type(),
 		}, v, tag, dcmd.name, map[string]bool{})
+		if err != nil {
+			return nil, err
+		}
 	}
 
 	for _, option := range k.postBuildOptions {
@@ -231,7 +227,6 @@ func (k *Kong) extraFlags() []*Flag {
 // Will return a ParseError if a *semantically* invalid command-line is encountered (as opposed to a syntactically
 // invalid one, which will report a normal error).
 func (k *Kong) Parse(args []string) (ctx *Context, err error) {
-	defer catch(&err)
 	ctx, err = Trace(k, args)
 	if err != nil {
 		return nil, err
@@ -398,12 +393,3 @@ func (k *Kong) LoadConfig(path string) (Resolver, error) {
 
 	return k.loader(r)
 }
-
-func catch(err *error) {
-	msg := recover()
-	if test, ok := msg.(Error); ok {
-		*err = test
-	} else if msg != nil {
-		panic(msg)
-	}
-}