Avoid to create unnecessary resources (aio-libs#2586)

Do not create a new resource when adding a route with the same
name and path of an existing resource

CHANGES/2586.feature

@@ -0,0 +1,2 @@
+Avoid to create a new resource when adding a route with the same
+name and path of the last added resource

aiohttp/web_urldispatcher.py

@@ -299,6 +299,10 @@ async def resolve(self, request):
         else:
             return None, allowed_methods
 
+    @abc.abstractmethod
+    def raw_match(self, path):
+        """Perform a raw match against path"""
+
     def __len__(self):
         return len(self._routes)
 
@@ -332,6 +336,9 @@ def _match(self, path):
         else:
             return None
 
+    def raw_match(self, path):
+        return self._path == path
+
     def get_info(self):
         return {'path': self._path}
 
@@ -400,6 +407,9 @@ def _match(self, path):
             return {key: unquote(value, unsafe='+') for key, value in
                     match.groupdict().items()}
 
+    def raw_match(self, path):
+        return self._formatter == path
+
     def get_info(self):
         return {'formatter': self._formatter,
                 'pattern': self._pattern}
@@ -830,6 +840,11 @@ def register_resource(self, resource):
     def add_resource(self, path, *, name=None):
         if path and not path.startswith('/'):
             raise ValueError("path should be started with / or be empty")
+        # Reuse last added resource if path and name are the same
+        if self._resources:
+            resource = self._resources[-1]
+            if resource.name == name and resource.raw_match(path):
+                return resource
         if not ('{' in path or '}' in path or ROUTE_RE.search(path)):
             url = URL(path)
             resource = PlainResource(url.raw_path, name=name)

tests/test_web_urldispatcher.py

@@ -342,3 +342,23 @@ async def handler(_):
     r = await client.head('/b')
     assert r.status == 405
     await r.release()
+
+
+@pytest.mark.parametrize("path", [
+    '/a',
+    '/{a}',
+])
+def test_reuse_last_added_resource(path):
+    """
+    Test that adding a route with the same name and path of the last added
+    resource doesn't create a new resource.
+    """
+    app = web.Application()
+
+    async def handler(request):
+        return web.Response()
+
+    app.router.add_get(path, handler, name="a")
+    app.router.add_post(path, handler, name="a")
+
+    assert len(app.router.resources()) == 1