Fixed inability to pass total_tokens as a keyword argument on the tri…

…o backend (#666)

Fixes #515.

docs/versionhistory.rst

@@ -7,6 +7,9 @@ This library adheres to `Semantic Versioning 2.0 <http://semver.org/>`_.
 
 - Added support for the Python 3.12 ``walk_up`` keyword argument in
   ``anyio.Path.relative_to()`` (PR by Colin Taylor)
+- Fixed passing ``total_tokens`` to ``anyio.CapacityLimiter()`` as a keyword argument
+  not working on the ``trio`` backend
+  (`#515 <https://github.com/agronholm/anyio/issues/515>`_)
 
 **4.2.0**
 

src/anyio/_backends/_trio.py

@@ -631,14 +631,24 @@ def set(self) -> None:
 
 class CapacityLimiter(BaseCapacityLimiter):
     def __new__(
-        cls, *args: Any, original: trio.CapacityLimiter | None = None
+        cls,
+        total_tokens: float | None = None,
+        *,
+        original: trio.CapacityLimiter | None = None,
     ) -> CapacityLimiter:
         return object.__new__(cls)
 
     def __init__(
-        self, *args: Any, original: trio.CapacityLimiter | None = None
+        self,
+        total_tokens: float | None = None,
+        *,
+        original: trio.CapacityLimiter | None = None,
     ) -> None:
-        self.__original = original or trio.CapacityLimiter(*args)
+        if original is not None:
+            self.__original = original
+        else:
+            assert total_tokens is not None
+            self.__original = trio.CapacityLimiter(total_tokens)
 
     async def __aenter__(self) -> None:
         return await self.__original.__aenter__()

tests/test_synchronization.py

@@ -689,3 +689,8 @@ async def use_limiter() -> None:
             backend=anyio_backend_name,
             backend_options=anyio_backend_options,
         )
+
+    async def test_total_tokens_as_kwarg(self) -> None:
+        # Regression test for #515
+        limiter = CapacityLimiter(total_tokens=1)
+        assert limiter.total_tokens == 1