From efd7f01c292b8b99164bc7010c19da38cadb2d08 Mon Sep 17 00:00:00 2001
From: Yurii Karabas <1998uriyyo@gmail.com>
Date: Mon, 3 May 2021 23:59:02 +0300
Subject: [PATCH] Add better exception msg for duplicated param names

---
 starlette/routing.py  |  9 +++++++++
 tests/test_routing.py | 14 ++++++++++++++
 2 files changed, 23 insertions(+)

diff --git a/starlette/routing.py b/starlette/routing.py
index 1e6ae0b55..2707bbf4a 100644
--- a/starlette/routing.py
+++ b/starlette/routing.py
@@ -107,6 +107,7 @@ def compile_path(
     """
     path_regex = "^"
     path_format = ""
+    duplicated_params = set()
 
     idx = 0
     param_convertors = {}
@@ -124,10 +125,18 @@ def compile_path(
         path_format += path[idx : match.start()]
         path_format += "{%s}" % param_name
 
+        if param_name in param_convertors:
+            duplicated_params.add(param_name)
+
         param_convertors[param_name] = convertor
 
         idx = match.end()
 
+    if duplicated_params:
+        names = ", ".join(sorted(duplicated_params))
+        ending = "s" if len(duplicated_params) > 1 else ""
+        raise ValueError(f"Duplicated param name{ending} {names} at path {path}")
+
     path_regex += re.escape(path[idx:]) + "$"
     path_format += path[idx:]
 
diff --git a/tests/test_routing.py b/tests/test_routing.py
index 8927c60cd..fff3332db 100644
--- a/tests/test_routing.py
+++ b/tests/test_routing.py
@@ -622,3 +622,17 @@ def test_partial_async_endpoint():
     cls_method_response = test_client.get("/cls")
     assert cls_method_response.status_code == 200
     assert cls_method_response.json() == {"arg": "foo"}
+
+
+def test_duplicated_param_names():
+    with pytest.raises(
+        ValueError,
+        match="Duplicated param name id at path /{id}/{id}",
+    ):
+        Route("/{id}/{id}", user)
+
+    with pytest.raises(
+        ValueError,
+        match="Duplicated param names id, name at path /{id}/{name}/{id}/{name}",
+    ):
+        Route("/{id}/{name}/{id}/{name}", user)