Warn on bool(strategy)

Author: Zac-HD

hypothesis-python/RELEASE.rst

@@ -0,0 +1,5 @@
+RELEASE_TYPE: minor
+
+This release defines ``__bool__()`` on :class:`~hypothesis.strategies.SearchStrategy`.
+It always returns ``True``, like before, but also emits a warning to help with
+cases where you intended to draw a value (:issue:`3463`).

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

@@ -29,6 +29,7 @@
 from hypothesis.control import _current_build_context, assume
 from hypothesis.errors import (
     HypothesisException,
+    HypothesisWarning,
     InvalidArgument,
     NonInteractiveExampleWarning,
     UnsatisfiedAssumption,
@@ -396,6 +397,14 @@ def __or__(self, other: "SearchStrategy[T]") -> "SearchStrategy[Union[Ex, T]]":
             raise ValueError(f"Cannot | a SearchStrategy with {other!r}")
         return OneOfStrategy((self, other))
 
+    def __bool__(self) -> bool:
+        warnings.warn(
+            f"bool({self!r}) is always True, did you mean to draw a value?",
+            HypothesisWarning,
+            stacklevel=2,
+        )
+        return True
+
     def validate(self) -> None:
         """Throw an exception if the strategy is not valid.
 

hypothesis-python/tests/cover/test_error_in_draw.py

@@ -11,6 +11,7 @@
 import pytest
 
 from hypothesis import given, strategies as st
+from hypothesis.errors import HypothesisWarning
 
 
 def test_error_is_in_finally():
@@ -25,3 +26,13 @@ def test(d):
         test()
 
     assert "[0, 1, -1]" in "\n".join(err.value.__notes__)
+
+
+@given(st.data())
+def test_warns_on_bool_strategy(data):
+    with pytest.warns(
+        HypothesisWarning,
+        match=r"bool\(.+\) is always True, did you mean to draw a value\?",
+    ):
+        if st.booleans():  # 'forgot' to draw from the strategy
+            pass