Router: add explicit error message when calling RegisterRoutes twice

Author: System-Glitch

router.go

@@ -138,9 +138,7 @@ func NewRouter(server *Server) *Router {
 
 // ClearRegexCache set internal router's regex cache used for route parameters optimisation to nil
 // so it can be garbage collected.
-// You don't need to call this function if you are using `goyave.Server`.
-// However, this method SHOULD be called by external tooling that build routers without starting the HTTP
-// server when they are done registering routes and subrouters.
+// You don't need to call this function if you are using `server.RegisterRoutes`.
 func (r *Router) ClearRegexCache() {
 	r.regexCache = nil
 	for _, subrouter := range r.subrouters {

server.go

@@ -490,6 +490,9 @@ func (s *Server) Start() error {
 // The router's regex cache is cleared after the `routeRegistrer` function returns.
 // This method should only be called once.
 func (s *Server) RegisterRoutes(routeRegistrer func(*Server, *Router)) {
+	if s.router.regexCache == nil {
+		panic(errors.NewSkip("router's regex cache has already been cleared, did you call RegisterRoutes twice?", 3))
+	}
 	routeRegistrer(s, s.router)
 	s.router.ClearRegexCache()
 }

server_test.go

@@ -340,6 +340,12 @@ func TestServer(t *testing.T) {
 			router.Get("/", func(_ *Response, _ *Request) {}).Name("base")
 		})
 		assert.NotNil(t, server.router.GetRoute("base"))
+
+		t.Run("panic_if_called_twice", func(t *testing.T) {
+			assert.PanicsWithError(t, "router's regex cache has already been cleared, did you call RegisterRoutes twice?", func() {
+				server.RegisterRoutes(func(_ *Server, _ *Router) {})
+			})
+		})
 	})
 
 	t.Run("Transaction", func(t *testing.T) {