[3.12] gh-112281: Allow Union with unhashable Annotated metadata (GH-112283) (#116213)

Co-authored-by: Nikita Sobolev <mail@sobolevn.me>
Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>

Lib/typing.py

@@ -314,19 +314,33 @@ def _unpack_args(args):
             newargs.append(arg)
     return newargs
 
-def _deduplicate(params):
+def _deduplicate(params, *, unhashable_fallback=False):
     # Weed out strict duplicates, preserving the first of each occurrence.
-    all_params = set(params)
-    if len(all_params) < len(params):
-        new_params = []
-        for t in params:
-            if t in all_params:
-                new_params.append(t)
-                all_params.remove(t)
-        params = new_params
-        assert not all_params, all_params
-    return params
+    try:
+        return dict.fromkeys(params)
+    except TypeError:
+        if not unhashable_fallback:
+            raise
+        # Happens for cases like `Annotated[dict, {'x': IntValidator()}]`
+        return _deduplicate_unhashable(params)
 
+def _deduplicate_unhashable(unhashable_params):
+    new_unhashable = []
+    for t in unhashable_params:
+        if t not in new_unhashable:
+            new_unhashable.append(t)
+    return new_unhashable
+
+def _compare_args_orderless(first_args, second_args):
+    first_unhashable = _deduplicate_unhashable(first_args)
+    second_unhashable = _deduplicate_unhashable(second_args)
+    t = list(second_unhashable)
+    try:
+        for elem in first_unhashable:
+            t.remove(elem)
+    except ValueError:
+        return False
+    return not t
 
 def _remove_dups_flatten(parameters):
     """Internal helper for Union creation and substitution.
@@ -341,7 +355,7 @@ def _remove_dups_flatten(parameters):
         else:
             params.append(p)
 
-    return tuple(_deduplicate(params))
+    return tuple(_deduplicate(params, unhashable_fallback=True))
 
 
 def _flatten_literal_params(parameters):
@@ -1548,7 +1562,10 @@ class _UnionGenericAlias(_NotIterable, _GenericAlias, _root=True):
     def __eq__(self, other):
         if not isinstance(other, (_UnionGenericAlias, types.UnionType)):
             return NotImplemented
-        return set(self.__args__) == set(other.__args__)
+        try:  # fast path
+            return set(self.__args__) == set(other.__args__)
+        except TypeError:  # not hashable, slow path
+            return _compare_args_orderless(self.__args__, other.__args__)
 
     def __hash__(self):
         return hash(frozenset(self.__args__))