check PrimitiveProvider.add_observation_callback instead

Author: Liam-DeVoe

hypothesis-python/docs/prolog.rst

@@ -117,6 +117,7 @@
 .. |PrimitiveProvider.draw_bytes| replace:: :func:`~hypothesis.internal.conjecture.providers.PrimitiveProvider.draw_bytes`
 .. |PrimitiveProvider.on_observation| replace:: :func:`~hypothesis.internal.conjecture.providers.PrimitiveProvider.on_observation`
 .. |PrimitiveProvider.per_test_case_context_manager| replace:: :func:`~hypothesis.internal.conjecture.providers.PrimitiveProvider.per_test_case_context_manager`
+.. |PrimitiveProvider.add_observation_callback| replace:: :data:`~hypothesis.internal.conjecture.providers.PrimitiveProvider.add_observation_callback`
 
 .. |AVAILABLE_PROVIDERS| replace:: :data:`~hypothesis.internal.conjecture.providers.AVAILABLE_PROVIDERS`
 .. |TESTCASE_CALLBACKS| replace:: :data:`~hypothesis.internal.observability.TESTCASE_CALLBACKS`

hypothesis-python/src/hypothesis/internal/conjecture/engine.py

@@ -848,10 +848,8 @@ def on_observation(observation: Observation) -> None:
                 # only for lifetime = "test_function" providers (guaranteed
                 # by this isinstance check)
                 and isinstance(self.provider, PrimitiveProvider)
-                # and the provider class overrode the default
-                # (see https://github.com/python/mypy/issues/14123 for type ignore)
-                and type(self.provider).on_observation
-                is not PrimitiveProvider.on_observation
+                # and the provider opted-in to observations
+                and self.provider.add_observation_callback
             )
             else nullcontext()
         )

hypothesis-python/src/hypothesis/internal/conjecture/providers.py

@@ -21,6 +21,7 @@
 from typing import (
     TYPE_CHECKING,
     Any,
+    ClassVar,
     Literal,
     Optional,
     TypedDict,
@@ -356,6 +357,15 @@ class PrimitiveProvider(abc.ABC):
     #: Only set this to ``True`` if it is necessary for your backend.
     avoid_realization = False
 
+    #: If ``True``, |PrimitiveProvider.on_observation| will be added as a
+    #: callback to |TESTCASE_CALLBACKS|, enabling observability during the lifetime
+    #: of this provider. If ``False``, |PrimitiveProvider.on_observation| will
+    #: never be called by Hypothesis.
+    #:
+    #: The opt-in behavior of observability is because enabling observability
+    #: might increase runtime or memory usage.
+    add_observation_callback: ClassVar[bool] = False
+
     def __init__(self, conjecturedata: Optional["ConjectureData"], /) -> None:
         self._cd = conjecturedata
 
@@ -551,6 +561,14 @@ def on_observation(self, observation: Observation) -> None:  # noqa: B027
         other callbacks in |TESTCASE_CALLBACKS|. This method is not called with
         ``observation["type"] in {"info", "alert", "error"}`` observations.
 
+        .. important::
+
+            For |PrimitiveProvider.on_observation| to be called by Hypothesis,
+            |PrimitiveProvider.add_observation_callback| must be set to ``True``,
+
+            |PrimitiveProvider.on_observation| is explicitly opt-in, as enabling
+            observability might increase runtime or memory usage.
+
         Calls to this method are guaranteed to alternate with calls to
         |PrimitiveProvider.per_test_case_context_manager|. For example:
 

hypothesis-python/tests/conjecture/test_alt_backend.py

@@ -722,6 +722,8 @@ def test_replay_choices():
 
 
 class ObservationProvider(TrivialProvider):
+    add_observation_callback = True
+
     def __init__(self, conjecturedata: "ConjectureData", /) -> None:
         super().__init__(conjecturedata)
         # calls to per_test_case_context_manager and on_observation alternate,