fixing alecthomas#137 error returned from Capture interface does not …

…contain position and is not wrapped

grammar.go

@@ -52,7 +52,7 @@ func (g *generatorContext) parseType(t reflect.Type) (_ node, returnedError erro
 		if slexer.NumField() == 0 {
 			return nil, fmt.Errorf("can not parse into empty struct %s", t)
 		}
-		defer decorate(&returnedError, func() string { return slexer.Field().Name })
+		defer decorate(&returnedError, nil, func() string { return slexer.Field().Name })
 		e, err := g.parseDisjunction(slexer)
 		if err != nil {
 			return nil, err

nodes.go

@@ -38,15 +38,25 @@ type node interface {
 	String() string
 }
 
-func decorate(err *error, name func() string) {
+func nearestPos(tokens []lexer.Token) *lexer.Position {
+	if len(tokens) == 0 {
+		return nil
+	}
+
+	return &tokens[0].Pos
+}
+
+func decorate(err *error, pos *lexer.Position, name func() string) {
 	if *err == nil {
 		return
 	}
-	if perr, ok := (*err).(Error); ok {
-		*err = Errorf(perr.Position(), "%s: %s", name(), perr.Message())
-	} else {
-		*err = &parseError{Msg: fmt.Sprintf("%s: %s", name(), *err)}
+
+	if pos == nil {
+		*err = fmt.Errorf("%s: %w", name(), err)
+		return
 	}
+
+	*err = Wrapf(*pos, *err, "%s", name())
 }
 
 // A node that proxies to an implementation that implements the Parseable interface.
@@ -550,7 +560,7 @@ func sizeOfKind(kind reflect.Kind) int {
 // For all other types, an attempt will be made to convert the string to the corresponding
 // type (int, float32, etc.).
 func setField(tokens []lexer.Token, strct reflect.Value, field structLexerField, fieldValue []reflect.Value) (err error) { // nolint: gocognit
-	defer decorate(&err, func() string { return strct.Type().Name() + "." + field.Name })
+	defer decorate(&err, nearestPos(tokens), func() string { return strct.Type().Name() + "." + field.Name })
 
 	f := strct.FieldByIndex(field.Index)
 

struct.go

@@ -122,7 +122,7 @@ func collectFieldIndexes(s reflect.Type) (out [][]int, err error) {
 	if s.Kind() != reflect.Struct {
 		return nil, fmt.Errorf("expected a struct but got %q", s)
 	}
-	defer decorate(&err, s.String)
+	defer decorate(&err, nil, s.String)
 	for i := 0; i < s.NumField(); i++ {
 		f := s.Field(i)
 		switch {