simplify treatment of typevar argument

Author: randolf-scholz

mypy/subtypes.py

@@ -2095,6 +2095,8 @@ def restrict_subtype_away(t: Type, s: Type, *, consider_runtime_isinstance: bool
     """
     p_t = get_proper_type(t)
     s_t = get_proper_type(s)
+    if isinstance(s_t, TypeVarType):
+        s = s_t.upper_bound
 
     if isinstance(p_t, UnionType):
         new_items = try_restrict_literal_union(p_t, s)
@@ -2109,15 +2111,7 @@ def restrict_subtype_away(t: Type, s: Type, *, consider_runtime_isinstance: bool
             [item for item in new_items if not isinstance(get_proper_type(item), UninhabitedType)]
         )
     elif isinstance(p_t, TypeVarType):
-        if isinstance(s_t, TypeVarType):
-            upper_bound = restrict_subtype_away(p_t.upper_bound, s_t.upper_bound)
-            upper_bound = get_proper_type(upper_bound)
-            return (
-                upper_bound
-                if isinstance(upper_bound, UninhabitedType)
-                else p_t.copy_modified(upper_bound=upper_bound)
-            )
-        return p_t.copy_modified(upper_bound=restrict_subtype_away(p_t.upper_bound, s_t))
+        return p_t.copy_modified(upper_bound=restrict_subtype_away(p_t.upper_bound, s))
 
     if consider_runtime_isinstance:
         if covers_at_runtime(t, s):