Warn on duplicate route names

sanic/app.py

@@ -1521,6 +1521,18 @@ async def _startup(self):
         self.signalize(self.config.TOUCHUP)
         self.finalize()
 
+        route_names = [route.name for route in self.router.routes]
+        duplicates = {
+            name for name in route_names if route_names.count(name) > 1
+        }
+        if duplicates:
+            names = ", ".join(duplicates)
+            deprecation(
+                f"Duplicate route names detected: {names}. In the future, "
+                "Sanic will enforce uniqueness in route naming.",
+                23.3,
+            )
+
         # TODO: Replace in v22.6 to check against apps in app registry
         if (
             self.__class__._uvloop_setting is not None

tests/test_routes.py

@@ -1266,3 +1266,22 @@ async def handler(request: Request):
 
     assert request.route.ctx.foo() == "foo"
     assert await request.route.ctx.bar() == 99
+
+
+@pytest.mark.asyncio
+async def test_duplicate_route_deprecation(app):
+    @app.route("/foo", name="duped")
+    async def handler_foo(request):
+        return text("...")
+
+    @app.route("/bar", name="duped")
+    async def handler_bar(request):
+        return text("...")
+
+    message = (
+        r"\[DEPRECATION v23\.3\] Duplicate route names detected: "
+        r"test_duplicate_route_deprecation\.duped\. In the future, "
+        r"Sanic will enforce uniqueness in route naming\."
+    )
+    with pytest.warns(DeprecationWarning, match=message):
+        await app._startup()