composite/overload compatibility

Author: Zac-HD

hypothesis-python/RELEASE.rst

@@ -0,0 +1,5 @@
+RELEASE_TYPE: patch
+
+This patch turns off a warning for functions decorated with
+:func:`typing.overload` and then :func:`~hypothesis.strategies.composite`,
+although only in that order (:issue:`3970`).

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

@@ -1810,7 +1810,7 @@ def _composite(f):
         )
     if params[0].default is not sig.empty:
         raise InvalidArgument("A default value for initial argument will never be used")
-    if not is_first_param_referenced_in_function(f):
+    if not (f is typing._overload_dummy or is_first_param_referenced_in_function(f)):
         note_deprecation(
             "There is no reason to use @st.composite on a function which "
             "does not call the provided draw() function internally.",

hypothesis-python/tests/cover/test_composite.py

@@ -9,6 +9,7 @@
 # obtain one at https://mozilla.org/MPL/2.0/.
 
 import sys
+import typing
 
 import pytest
 
@@ -204,3 +205,18 @@ def my_integers(draw: st.DrawFn) -> st.SearchStrategy[int]:
 
     assert len(w.list) == 1
     assert w.list[0].filename == __file__  # check stacklevel points to user code
+
+
+def test_composite_allows_overload_without_draw():
+    # See https://github.com/HypothesisWorks/hypothesis/issues/3970
+    @st.composite
+    @typing.overload
+    def overloaded(draw: st.DrawFn, *, x: int) -> typing.Literal[True]: ...
+
+    @st.composite
+    @typing.overload
+    def overloaded(draw: st.DrawFn, *, x: str) -> typing.Literal[False]: ...
+
+    @st.composite
+    def overloaded(draw: st.DrawFn, *, x: typing.Union[int, str]) -> bool:
+        return draw(st.just(isinstance(x, int)))