[3.12] Fix AsyncResolver not using the loop argument (#10951)

fixes #10787

Author: bdraco

CHANGES/10951.bugfix.rst

@@ -0,0 +1 @@
+Fixed :py:class:`~aiohttp.resolver.AsyncResolver` not using the ``loop`` argument in versions 3.x where it should still be supported -- by :user:`bdraco`.

aiohttp/resolver.py

@@ -94,7 +94,7 @@ def __init__(
         if aiodns is None:
             raise RuntimeError("Resolver requires aiodns library")
 
-        self._loop = asyncio.get_running_loop()
+        self._loop = loop or asyncio.get_running_loop()
         self._manager: Optional[_DNSResolverManager] = None
         # If custom args are provided, create a dedicated resolver instance
         # This means each AsyncResolver with custom args gets its own

tests/test_resolver.py

@@ -711,3 +711,37 @@ async def test_async_resolver_close_with_none_resolver() -> None:
 
         # This should not raise AttributeError
         await resolver.close()
+
+
+@pytest.mark.skipif(aiodns is None, reason="aiodns required")
+def test_async_resolver_uses_provided_loop() -> None:
+    """Test that AsyncResolver uses the loop parameter when provided."""
+    # Create a custom event loop
+    custom_loop = asyncio.new_event_loop()
+
+    try:
+        # Need to set the loop as current for get_running_loop() to work
+        asyncio.set_event_loop(custom_loop)
+
+        # Create resolver with explicit loop parameter
+        resolver = AsyncResolver(loop=custom_loop)
+
+        # Check that the resolver uses the provided loop
+        assert resolver._loop is custom_loop
+    finally:
+        asyncio.set_event_loop(None)
+        custom_loop.close()
+
+
+@pytest.mark.skipif(aiodns is None, reason="aiodns required")
+@pytest.mark.usefixtures("check_no_lingering_resolvers")
+async def test_async_resolver_uses_running_loop_when_none_provided() -> None:
+    """Test that AsyncResolver uses get_running_loop() when no loop is provided."""
+    # Create resolver without loop parameter
+    resolver = AsyncResolver()
+
+    # Check that the resolver uses the current running loop
+    assert resolver._loop is asyncio.get_running_loop()
+
+    # Clean up
+    await resolver.close()