Update ancestors parameter for WalkFunc for matcher subrouters

Fixes #263

mux.go

@@ -308,10 +308,12 @@ func (r *Router) walk(walkFn WalkFunc, ancestors []*Route) error {
 		}
 		for _, sr := range t.matchers {
 			if h, ok := sr.(*Router); ok {
+				ancestors = append(ancestors, t)
 				err := h.walk(walkFn, ancestors)
 				if err != nil {
 					return err
 				}
+				ancestors = ancestors[:len(ancestors)-1]
 			}
 		}
 		if h, ok := t.handler.(*Router); ok {

mux_test.go

@@ -11,6 +11,7 @@ import (
 	"fmt"
 	"net/http"
 	"net/url"
+	"reflect"
 	"strings"
 	"testing"
 )
@@ -1382,22 +1383,38 @@ func TestWalkNested(t *testing.T) {
 	l2 := l1.PathPrefix("/l").Subrouter()
 	l2.Path("/a")
 
-	paths := []string{"/g", "/g/o", "/g/o/r", "/g/o/r/i", "/g/o/r/i/l", "/g/o/r/i/l/l", "/g/o/r/i/l/l/a"}
+	testCases := []struct {
+		path      string
+		ancestors []*Route
+	}{
+		{"/g", []*Route{}},
+		{"/g/o", []*Route{g.parent.(*Route)}},
+		{"/g/o/r", []*Route{g.parent.(*Route), o.parent.(*Route)}},
+		{"/g/o/r/i", []*Route{g.parent.(*Route), o.parent.(*Route), r.parent.(*Route)}},
+		{"/g/o/r/i/l", []*Route{g.parent.(*Route), o.parent.(*Route), r.parent.(*Route), i.parent.(*Route)}},
+		{"/g/o/r/i/l/l", []*Route{g.parent.(*Route), o.parent.(*Route), r.parent.(*Route), i.parent.(*Route), l1.parent.(*Route)}},
+		{"/g/o/r/i/l/l/a", []*Route{g.parent.(*Route), o.parent.(*Route), r.parent.(*Route), i.parent.(*Route), l1.parent.(*Route), l2.parent.(*Route)}},
+	}
+
 	idx := 0
 	err := router.Walk(func(route *Route, router *Router, ancestors []*Route) error {
-		path := paths[idx]
+		path := testCases[idx].path
 		tpl := route.regexp.path.template
 		if tpl != path {
 			t.Errorf(`Expected %s got %s`, path, tpl)
 		}
+		currWantAncestors := testCases[idx].ancestors
+		if !reflect.DeepEqual(currWantAncestors, ancestors) {
+			t.Errorf(`Expected %+v got %+v`, currWantAncestors, ancestors)
+		}
 		idx++
 		return nil
 	})
 	if err != nil {
 		panic(err)
 	}
-	if idx != len(paths) {
+	if idx != len(testCases) {
-		t.Errorf("Expected %d routes, found %d", len(paths), idx)
+		t.Errorf("Expected %d routes, found %d", len(testCases), idx)
 	}
 }