tree: Fix bug where loop index is not decremented.

Also add test to validate fix.

fixes gin-gonic#3459

Signed-off-by: Kristian Svalland <kristian.svalland@gmail.com>

routes_test.go

@@ -670,3 +670,22 @@ func TestRouteContextHoldsFullPath(t *testing.T) {
 	w := PerformRequest(router, http.MethodGet, "/not-found")
 	assert.Equal(t, http.StatusNotFound, w.Code)
 }
+
+func TestEngineHandleMethodNotAllowedCornerCase(t *testing.T) {
+	r := New()
+	r.HandleMethodNotAllowed = true
+
+	base := r.Group("base")
+	base.GET("/metrics", handlerTest1)
+
+	v1 := base.Group("v1")
+
+	v1.GET("/:id/devices", handlerTest1)
+	v1.GET("/user/:id/groups", handlerTest1)
+
+	v1.GET("/orgs/:id", handlerTest1)
+	v1.DELETE("/orgs/:id", handlerTest1)
+
+	w := PerformRequest(r, "GET", "/base/v1/user/groups")
+	assert.Equal(t, http.StatusNotFound, w.Code)
+}

tree.go

@@ -462,6 +462,7 @@ walk: // Outer loop for walking the tree
 						for l := len(*skippedNodes); l > 0; {
 							skippedNode := (*skippedNodes)[l-1]
 							*skippedNodes = (*skippedNodes)[:l-1]
+							l--
 							if strings.HasSuffix(skippedNode.path, path) {
 								path = skippedNode.path
 								n = skippedNode.node
@@ -579,6 +580,7 @@ walk: // Outer loop for walking the tree
 				for l := len(*skippedNodes); l > 0; {
 					skippedNode := (*skippedNodes)[l-1]
 					*skippedNodes = (*skippedNodes)[:l-1]
+					l--
 					if strings.HasSuffix(skippedNode.path, path) {
 						path = skippedNode.path
 						n = skippedNode.node
@@ -636,6 +638,7 @@ walk: // Outer loop for walking the tree
 			for l := len(*skippedNodes); l > 0; {
 				skippedNode := (*skippedNodes)[l-1]
 				*skippedNodes = (*skippedNodes)[:l-1]
+				l--
 				if strings.HasSuffix(skippedNode.path, path) {
 					path = skippedNode.path
 					n = skippedNode.node