adjust test case and fix enums without members being collapsed to nev…

…er which is also the base of all types

mypy/typeops.py

@@ -897,18 +897,16 @@ class Status(Enum):
         items = [
             try_expanding_sum_type_to_union(item, target_fullname) for item in typ.relevant_items()
         ]
-        return make_simplified_union(items, contract_literals=False)
     elif isinstance(typ, Instance) and typ.type.fullname == target_fullname:
         if typ.type.is_enum:
-            return make_simplified_union(
-                [LiteralType(name, typ) for name in typ.get_enum_values()], contract_literals=False
-            )
+            items = [LiteralType(name, typ) for name in typ.get_enum_values()]
         elif typ.type.fullname == "builtins.bool":
-            return make_simplified_union(
-                [LiteralType(True, typ), LiteralType(False, typ)], contract_literals=False
-            )
+            items = [LiteralType(True, typ), LiteralType(False, typ)]
+    else:
+        return typ
 
-    return typ
+    # if the expanded union would be `Never` leave the type as is
+    return typ if not items else make_simplified_union(items, contract_literals=False)
 
 
 def try_contracting_literals_in_union(types: Sequence[Type]) -> list[ProperType]:

test-data/unit/check-enum.test

@@ -2230,24 +2230,22 @@ reveal_type(Foo.Baz.value)  # N: Revealed type is "Any"
 [typing fixtures/typing-full.pyi]
 
 
-[case testEnumWithAnnotationOnly]
+[case testEnumWithImplicitMembersUsingAnnotationOnly]
 # flags: --warn-unreachable
 import enum
 
 
 class E(enum.IntEnum):
-    A: int  # E: Enum members must be left unannotated \
-            # N: See https://typing.readthedocs.io/en/latest/spec/enums.html#defining-members
-    B: int  # E: Enum members must be left unannotated \
-            # N: See https://typing.readthedocs.io/en/latest/spec/enums.html#defining-members
+    A: int
+    B: int
 
 
 def do_check(value: E) -> None:
     reveal_type(value)  # N: Revealed type is "__main__.E"
     if value is E.A:
         return
 
-    reveal_type(value)  # N: Revealed type is "Literal[__main__.E.B]"
+    reveal_type(value)  # N: Revealed type is "__main__.E"
     "should be reachable"
 
 [builtins fixtures/primitives.pyi]