Improve handling of fwd-reference in get_type_hints. Closes #3519

hypothesis-python/RELEASE.rst

@@ -0,0 +1,6 @@
+RELEASE_TYPE: minor
+
+This release improves Hypothesis' ability to resolve forward references in 
+type annotations. It fixes a bug that prevented 
+:func:`~hypothesis.strategies.builds` from being used with `pydantic models that
+possess updated forward references <https://pydantic-docs.helpmanual.io/usage/postponed_annotations/>`__. See :issue:`3519`.

hypothesis-python/src/hypothesis/internal/compat.py

@@ -111,8 +111,13 @@ def get_type_hints(thing):
                     and is_a_type(p.annotation)
                     and p.annotation is not p.empty
                 ):
+                    if isinstance(p.annotation, typing.ForwardRef) and not isinstance(
+                        hints[p.name], typing.ForwardRef
+                    ):
+                        continue
+
                     if p.default is None:
-                        hints[p.name] = typing.Optional[p.annotation]
+                        hints[p.name] = typing.Optional[p.annotation]  # type: ignore
                     else:
                         hints[p.name] = p.annotation
     except (AttributeError, TypeError, NameError):  # pragma: no cover

hypothesis-python/tests/cover/test_compat.py

@@ -9,7 +9,9 @@
 # obtain one at https://mozilla.org/MPL/2.0/.
 
 import math
-from inspect import Parameter, Signature
+from dataclasses import dataclass
+from inspect import Parameter, Signature, signature
+from typing import ForwardRef
 
 import pytest
 
@@ -45,3 +47,24 @@ class WeirdSig:
 
 def test_no_type_hints():
     assert get_type_hints(WeirdSig) == {}
+
+
+@dataclass
+class Foo:
+    x: "Foo"
+
+
+Foo.__signature__ = signature(Foo).replace(  # type: ignore
+    parameters=[
+        Parameter(
+            "x",
+            Parameter.POSITIONAL_OR_KEYWORD,
+            annotation=ForwardRef("Foo"),
+        )
+    ]
+)
+
+
+def test_resolve_fwd_refs():
+    # See: https://github.com/HypothesisWorks/hypothesis/issues/3519
+    assert get_type_hints(Foo)["x"] is Foo