Fix from_type failure on collections.abc.Callable[..., None]

Author: sobolevn

hypothesis-python/RELEASE.rst

@@ -0,0 +1,4 @@
+RELEASE_TYPE: patch
+
+Fix :func:`~hypothesis.strategies.from_type`
+on :class:`collections.abc.Callable` returning :const:`None`.

hypothesis-python/src/hypothesis/strategies/_internal/types.py

@@ -1031,6 +1031,9 @@ def resolve_Callable(thing):
             "Consider using an explicit strategy, or opening an issue."
         )
 
+    if get_origin(thing) is collections.abc.Callable and return_type is None:
+        return_type = type(None)
+
     return st.functions(
         like=(lambda *a, **k: None) if args_types else (lambda: None),
         returns=st.from_type(return_type),

hypothesis-python/tests/cover/test_lookup_py39.py

@@ -8,6 +8,7 @@
 # v. 2.0. If a copy of the MPL was not distributed with this file, You can
 # obtain one at https://mozilla.org/MPL/2.0/.
 
+import collections.abc
 import dataclasses
 import sys
 import typing
@@ -174,3 +175,9 @@ def __iter__(self):
 @given(...)
 def test_grouped_protocol_strategy(x: typing.Annotated[int, LazyStrategyAnnotation()]):
     assert x is sentinel
+
+
+def test_collections_abc_callable_none():
+    # https://github.com/HypothesisWorks/hypothesis/issues/4192
+    s = st.from_type(collections.abc.Callable[[None], None])
+    assert_all_examples(s, lambda x: callable(x) and x(None) is None)