Before you murder me, a constraint T <: (A | B) where T: (A | C) can be satisfied by T = A

Author: sterliakov

mypy/constraints.py

@@ -571,21 +571,21 @@ def any_constraints(options: list[list[Constraint] | None], *, eager: bool) -> l
 def filter_satisfiable(option: list[Constraint] | None) -> list[Constraint] | None:
     """Keep only constraints that can possibly be satisfied.
 
-    Currently, we filter out constraints where target is not a subtype of the upper bound.
+    Currently, we filter out constraints where target does not overlap with the upper bound.
     Since those can be never satisfied. We may add more cases in future if it improves type
     inference.
     """
+    from mypy.meet import is_overlapping_types
+
     if not option:
         return option
 
     satisfiable = []
     for c in option:
         if isinstance(c.origin_type_var, TypeVarType) and c.origin_type_var.values:
-            if any(
-                mypy.subtypes.is_subtype(c.target, value) for value in c.origin_type_var.values
-            ):
+            if any(is_overlapping_types(c.target, value) for value in c.origin_type_var.values):
                 satisfiable.append(c)
-        elif mypy.subtypes.is_subtype(c.target, c.origin_type_var.upper_bound):
+        elif is_overlapping_types(c.target, c.origin_type_var.upper_bound):
             satisfiable.append(c)
     if not satisfiable:
         return None