Improved get_type_hints() for classes with forward references

hypothesis-python/RELEASE.rst

@@ -0,0 +1,5 @@
+RELEASE_TYPE: patch
+
+This patch improves the internals of :func:`~hypothesis.strategies.builds` type
+inference, to handle recursive forward references in certain dataclasses.
+This is useful for e.g. :pypi:`hypothesmith`'s forthcoming :pypi:`LibCST` mode.

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

@@ -125,14 +125,25 @@ def get_type_hints(thing):
 else:
 
  def get_type_hints(thing):
- if inspect.isclass(thing) and not hasattr(thing, "__signature__"):
- if is_typed_named_tuple(thing):
- # Special handling for typing.NamedTuple
- return thing._field_types # type: ignore
- thing = thing.__init__ # type: ignore
+ """Like the typing version, but tries harder and never errors.
+
+ Tries harder: if the thing to inspect is a class but typing.get_type_hints
+ raises an error or returns no hints, then this function will try calling it
+ on the __init__ method. This second step often helps with user-defined
+ classes on older versions of Python.
+
+ Never errors: instead of raising TypeError for uninspectable objects, or
+ NameError for unresolvable forward references, just return an empty dict.
+ """
  try:
- return typing.get_type_hints(thing)
- except TypeError:
+ hints = typing.get_type_hints(thing)
+ except (TypeError, NameError):
+ hints = {}
+ if hints or not inspect.isclass(thing):
+ return hints
+ try:
+ return typing.get_type_hints(thing.__init__)
+ except (TypeError, NameError, AttributeError):
  return {}
 
 

hypothesis-python/tests/conftest.py

@@ -29,6 +29,8 @@
 # Skip collection of tests which require the Django test runner,
 # or that don't work on the current version of Python.
 collect_ignore_glob = ["django/*"]
+if sys.version_info < (3, 6): # Remove after dropping Python 3.5
+ collect_ignore_glob.append("cover/*py36*")
 if sys.version_info < (3, 8):
  collect_ignore_glob.append("cover/*py38*")
 

hypothesis-python/tests/cover/test_lookup_py36.py

@@ -0,0 +1,33 @@
+# This file is part of Hypothesis, which may be found at
+# https://github.com/HypothesisWorks/hypothesis/
+#
+# Most of this work is copyright (C) 2013-2020 David R. MacIver
+# (david@drmaciver.com), but it contains contributions by others. See
+# CONTRIBUTING.rst for a full list of people who may hold copyright, and
+# consult the git log if you need to determine who owns an individual
+# contribution.
+#
+# This Source Code Form is subject to the terms of the Mozilla Public License,
+# 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/.
+#
+# END HEADER
+
+import typing
+
+import pytest
+
+from hypothesis import given, strategies as st
+from hypothesis.internal.compat import PYPY
+
+
+class TreeForwardRefs(typing.NamedTuple):
+ val: int
+ l: typing.Optional["TreeForwardRefs"]
+ r: typing.Optional["TreeForwardRefs"]
+
+
+@pytest.mark.skipif(PYPY, reason="pypy36 does not resolve the forward refs")
+@given(st.builds(TreeForwardRefs))
+def test_resolves_forward_references_outside_annotations(t):
+ assert isinstance(t, TreeForwardRefs)

hypothesis-python/tests/cover/test_lookup_py38.py

@@ -13,6 +13,7 @@
 #
 # END HEADER
 
+import dataclasses
 import typing
 
 import pytest
@@ -101,3 +102,14 @@ def test_layered_optional_key_is_optional():
  # Optional keys are not currently supported, as PEP-589 leaves no traces
  # at runtime. See https://github.com/python/cpython/pull/17214
  find_any(from_type(C), lambda d: "b" not in d)
+
+
+@dataclasses.dataclass()
+class Node:
+ left: typing.Union["Node", int]
+ right: typing.Union["Node", int]
+
+
+@given(st.builds(Node))
+def test_can_resolve_recursive_dataclass(val):
+ assert isinstance(val, Node)