Support enum Literals in the enum plugin

mypy/plugins/enums.py

@@ -209,8 +209,11 @@ class SomeEnum:
                 return make_simplified_union(cast(Sequence[Type], proper_types))
         return ctx.default_attr_type
 
-    assert isinstance(ctx.type, Instance)
-    info = ctx.type.type
+    assert isinstance(ctx.type, (Instance, LiteralType))
+    if isinstance(ctx.type, Instance):
+        info = ctx.type.type
+    else:
+        info = ctx.type.fallback.type
 
     # As long as mypy doesn't understand attribute creation in __new__,
     # there is no way to predict the value type if the enum class has a
@@ -241,15 +244,20 @@ def _extract_underlying_field_name(typ: Type) -> str | None:
     We can examine this Literal fallback to retrieve the string.
     """
     typ = get_proper_type(typ)
-    if not isinstance(typ, Instance):
+    if not isinstance(typ, (Instance, LiteralType)):
         return None
 
-    if not typ.type.is_enum:
-        return None
+    if isinstance(typ, Instance):
+        if not typ.type.is_enum:
+            return None
 
-    underlying_literal = typ.last_known_value
-    if underlying_literal is None:
-        return None
+        underlying_literal = typ.last_known_value
+        if underlying_literal is None:
+            return None
+    else:
+        underlying_literal = typ
+        if not typ.is_enum_literal():
+            return None
 
     # The checks above have verified this LiteralType is representing an enum value,
     # which means the 'value' field is guaranteed to be the name of the enum field

test-data/unit/check-enum.test

@@ -2125,3 +2125,32 @@ class AllPartialList(Enum):
 
     def check(self) -> None:
         reveal_type(self.value)  # N: Revealed type is "builtins.list[Any]"
+
+[case testEnumLiteralsSupportedByPlugin]
+from enum import Enum
+from typing_extensions import Literal
+
+class E(Enum):
+    A = 1
+    B = 2
+
+x: Literal[E.A]
+reveal_type(x)  # N: Revealed type is "Literal[__main__.E.A]"
+reveal_type(x.value)  # N: Revealed type is "Literal[1]?"
+reveal_type(x.name)  # N: Revealed type is "Literal['A']?"
+
+e: E
+if e is E.A:
+    reveal_type(e)  # N: Revealed type is "Literal[__main__.E.A]"
+    reveal_type(e.value)  # N: Revealed type is "Literal[1]?"
+    reveal_type(e.name)  # N: Revealed type is "Literal['A']?"
+else:
+    reveal_type(e)  # N: Revealed type is "Literal[__main__.E.B]"
+    reveal_type(e.value)  # N: Revealed type is "Literal[2]?"
+    reveal_type(e.name)  # N: Revealed type is "Literal['B']?"
+
+y: Literal[E.A, E.B]
+reveal_type(y)  # N: Revealed type is "Union[Literal[__main__.E.A], Literal[__main__.E.B]]"
+reveal_type(y.value)  # N: Revealed type is "Any"
+reveal_type(y.name)  # N: Revealed type is "builtins.str"
+[builtins fixtures/tuple.pyi]