FIX: We were occasionally reusing an exhausted generator in Union con…

…structor.

PiperOrigin-RevId: 323697283

pytype/abstract.py

@@ -1435,7 +1435,7 @@ def __init__(self, options, vm):
     assert options
     self.options = list(options)
     # TODO(rechen): Don't allow a mix of formal and non-formal types
-    self.formal = any(t.formal for t in options)
+    self.formal = any(t.formal for t in self.options)
     mixin.NestedAnnotation.init_mixin(self)
 
   def __repr__(self):

pytype/tests/test_typevar.py

@@ -419,6 +419,16 @@ def test_recursive_alias(self):
     """)
     self.assertErrorRegexes(errors, {"e": r"Recursive.*X"})
 
+  def test_use_unsupported_typevar(self):
+    # Test that we don't crash when using this pattern (b/162274390)
+    # Note that it throws four distinct errors, which is less than ideal.
+    self.CheckWithErrors("""
+      from typing import List, TypeVar, Union
+      T = TypeVar("T")
+      Tree = Union[T, List['Tree']]  # not-supported-yet  # not-supported-yet
+      def f(x: Tree[int]): ...  # invalid-typevar  # unsupported-operands
+    """)
+
   def test_type_of_typevar(self):
     self.Check("""
       from typing import Sequence, TypeVar