Allow 0 tokens in a CapacityLimiter instantiated outside an event loop

docs/versionhistory.rst

@@ -10,6 +10,10 @@ This library adheres to `Semantic Versioning 2.0 <http://semver.org/>`_.
   when an async test raise an outcome exception (e.g., ``pytest.skip()``, ``pytest.xfail()``,
   or ``pytest.fail()``)
   (`#1179 <https://github.com/agronholm/anyio/issues/1179>`_; PR by @EmmanuelNiyonshuti)
+- Fixed ``CapacityLimiter.total_tokens`` rejecting a value of ``0`` when the limiter was
+  instantiated outside of an event loop, contradicting the documented behavior of
+  allowing 0 total tokens
+  (`#1183 <https://github.com/agronholm/anyio/pull/1183>`_; PR by @nyxst4ck)
 
 **4.14.0**
 

src/anyio/_core/_synchronization.py

@@ -684,8 +684,8 @@ def total_tokens(self) -> float:
     def total_tokens(self, value: float) -> None:
         if not isinstance(value, int) and value is not math.inf:
             raise TypeError("total_tokens must be an int or math.inf")
-        elif value < 1:
-            raise ValueError("total_tokens must be >= 1")
+        elif value < 0:
+            raise ValueError("total_tokens must be >= 0")
 
         if self._internal_limiter is None:
             self._total_tokens = value

tests/test_synchronization.py

@@ -920,6 +920,14 @@ async def use_limiter() -> None:
             backend_options=anyio_backend_options,
         )
 
+    def test_zero_tokens_outside_event_loop(self) -> None:
+        # Regression test for the CapacityLimiterAdapter setter rejecting 0,
+        # which contradicted the 4.12 behavior of allowing 0 total tokens
+        limiter = CapacityLimiter(1)
+        limiter.total_tokens = 0
+        assert limiter.total_tokens == 0
+        assert CapacityLimiter(0).total_tokens == 0
+
     async def test_total_tokens_as_kwarg(self) -> None:
         # Regression test for #515
         limiter = CapacityLimiter(total_tokens=1)