From 9ce72fe0fcdae509884f8ccc7ab136fff76738d8 Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@koston.org>
Date: Thu, 1 Aug 2024 11:55:05 -0500
Subject: [PATCH] Fix url dispatcher index when variable is preceded by a fixed
 string after a slash (#8566)

(cherry picked from commit f3a1afc51665d9d2180606f250f492a61623ac6b)
---
 CHANGES/8566.bugfix.rst         |  1 +
 aiohttp/web_urldispatcher.py    | 10 ++++++++--
 tests/test_web_urldispatcher.py | 24 ++++++++++++++++++++++++
 3 files changed, 33 insertions(+), 2 deletions(-)
 create mode 100644 CHANGES/8566.bugfix.rst

diff --git a/CHANGES/8566.bugfix.rst b/CHANGES/8566.bugfix.rst
new file mode 100644
index 00000000000..61365c0bb61
--- /dev/null
+++ b/CHANGES/8566.bugfix.rst
@@ -0,0 +1 @@
+Fixed url dispatcher index not matching when a variable is preceded by a fixed string after a slash -- by :user:`bdraco`.
diff --git a/aiohttp/web_urldispatcher.py b/aiohttp/web_urldispatcher.py
index e26fd9dc7a6..a490e100ab3 100644
--- a/aiohttp/web_urldispatcher.py
+++ b/aiohttp/web_urldispatcher.py
@@ -1131,8 +1131,14 @@ def register_resource(self, resource: AbstractResource) -> None:
 
     def _get_resource_index_key(self, resource: AbstractResource) -> str:
         """Return a key to index the resource in the resource index."""
-        # strip at the first { to allow for variables
-        return resource.canonical.partition("{")[0].rstrip("/") or "/"
+        if "{" in (index_key := resource.canonical):
+            # strip at the first { to allow for variables, and than
+            # rpartition at / to allow for variable parts in the path
+            # For example if the canonical path is `/core/locations{tail:.*}`
+            # the index key will be `/core` since index is based on the
+            # url parts split by `/`
+            index_key = index_key.partition("{")[0].rpartition("/")[0]
+        return index_key.rstrip("/") or "/"
 
     def index_resource(self, resource: AbstractResource) -> None:
         """Add a resource to the resource index."""
diff --git a/tests/test_web_urldispatcher.py b/tests/test_web_urldispatcher.py
index 1cda0980cc0..a799f4ba146 100644
--- a/tests/test_web_urldispatcher.py
+++ b/tests/test_web_urldispatcher.py
@@ -937,3 +937,27 @@ async def get(self) -> web.Response:
     r = await client.get("///a")
     assert r.status == 200
     await r.release()
+
+
+async def test_route_with_regex(aiohttp_client: AiohttpClient) -> None:
+    """Test a route with a regex preceded by a fixed string."""
+    app = web.Application()
+
+    async def handler(request: web.Request) -> web.Response:
+        assert isinstance(request.match_info._route.resource, Resource)
+        return web.Response(text=request.match_info._route.resource.canonical)
+
+    app.router.add_get("/core/locations{tail:.*}", handler)
+    client = await aiohttp_client(app)
+
+    r = await client.get("/core/locations/tail/here")
+    assert r.status == 200
+    assert await r.text() == "/core/locations{tail}"
+
+    r = await client.get("/core/locations_tail_here")
+    assert r.status == 200
+    assert await r.text() == "/core/locations{tail}"
+
+    r = await client.get("/core/locations_tail;id=abcdef")
+    assert r.status == 200
+    assert await r.text() == "/core/locations{tail}"