Fix: don't crash on dataclass.FieldInstance objects without a default.

PiperOrigin-RevId: 318389448

pytype/output.py

@@ -218,6 +218,8 @@ def value_to_pytd_type(self, node, v, seen, view):
     elif isinstance(v, typing_overlay.TypeVar):
       return pytd.NamedType("__builtin__.type")
     elif isinstance(v, dataclass_overlay.FieldInstance):
+      if not v.default:
+        return pytd.AnythingType()
       return pytd_utils.JoinTypes(
           self.value_to_pytd_type(node, d, seen, view)
           for d in v.default.data)

pytype/tests/py3/test_dataclasses.py

@@ -480,4 +480,19 @@ class Foo(object):
           def __init__(self, x: bool, y: int, z: str) -> None: ...
       """)
 
+  def test_redefine_field(self):
+    # Tests that pytype can infer types for this (simplified) snippet of code
+    # from flax.struct.py.
+    ty = self.Infer("""
+      import dataclasses
+      def field(**kwargs):
+        return dataclasses.field(**kwargs)
+    """)
+    self.assertTypesMatchPytd(ty, """
+      from typing import Any
+      dataclasses: module
+      def field(**kwargs) -> Any: ...
+    """)
+
+
 test_base.main(globals(), __name__ == "__main__")