fix: provide clear error when importing VerifiedRoutes instead of using

lib/phoenix/verified_routes.ex

@@ -925,7 +925,19 @@ defmodule Phoenix.VerifiedRoutes do
   defp to_param(data), do: Phoenix.Param.to_param(data)
 
   defp build_route(route_ast, sigil_p, env, endpoint_ctx, router) do
-    config = Module.get_attribute(env.module, :phoenix_verified_config, [])
+    config = Module.get_attribute(env.module, :phoenix_verified_config)
+
+    if is_nil(config) do
+      raise ArgumentError, """
+      attempted to use Phoenix.VerifiedRoutes without calling `use Phoenix.VerifiedRoutes` first.
+
+      You must use `use Phoenix.VerifiedRoutes` with the appropriate options instead of importing it:
+
+          use Phoenix.VerifiedRoutes, endpoint: MyAppWeb.Endpoint, router: MyAppWeb.Router
+
+      See the documentation for more details on configuration options.
+      """
+    end
 
     router =
       case Macro.expand(router, env) do

test/phoenix/verified_routes_test.exs

@@ -302,6 +302,20 @@ defmodule Phoenix.VerifiedRoutesTest do
     :code.delete(__MODULE__.SigilPPrefix)
   end
 
+  test "~p raises when VerifiedRoutes is imported instead of used" do
+    assert_raise ArgumentError,
+                 ~r|attempted to use Phoenix.VerifiedRoutes without calling|,
+                 fn ->
+                   defmodule ImportedVerifiedRoutes do
+                     import Phoenix.VerifiedRoutes
+                     def test, do: ~p"/posts/1"
+                   end
+                 end
+  after
+    :code.purge(__MODULE__.ImportedVerifiedRoutes)
+    :code.delete(__MODULE__.ImportedVerifiedRoutes)
+  end
+
   test "path arities" do
     assert path(Endpoint, ~p"/posts/1") == "/posts/1"
     assert path(conn_with_endpoint(), ~p"/posts/1") == "/posts/1"