Fix: compare unresolved late annotations using their expressions.

Previously, they were compared using their types, which for unresolved
annotations is always Unsolvable, so checks like `LateAnnotation(expr='Z',
type=None) in {LateAnnotation(expr='Y', type=None)}` would incorrectly succeed.
PiperOrigin-RevId: 320666829

pytype/abstract.py

@@ -1184,10 +1184,10 @@ def __repr__(self):
   # set/dict comparisons.
 
   def __hash__(self):
-    return hash(self._type)
+    return hash(self._type) if self.resolved else hash(self.expr)
 
   def __eq__(self, other):
-    return self._type == other
+    return hash(self) == hash(other)
 
   def __getattribute__(self, name):
     if name == "_attribute_names" or name in self._attribute_names:

pytype/tests/py3/test_annotations.py

@@ -1007,7 +1007,8 @@ def test_forward_reference_in_type_alias(self):
     self.Check("""
       from typing import List
       X = List["Y"]
-      Y = List[int]
+      Y = List["Z"]
+      Z = List[int]
     """)
 
   def test_fully_quoted_annotation(self):