Support type alias as Literal (#8014)

Resolves #7996

Author: TH3CHARLie

mypy/semanal.py

@@ -3621,7 +3621,6 @@ def visit_member_expr(self, expr: MemberExpr) -> None:
                         type_info = self.type
             elif isinstance(base.node, TypeAlias) and base.node.no_args:
                 assert isinstance(base.node.target, ProperType)
-                # TODO: support chained aliases.
                 if isinstance(base.node.target, Instance):
                     type_info = base.node.target.type
 
@@ -3969,6 +3968,10 @@ def lookup_qualified(self, name: str, ctx: Context,
                     namespace = node.fullname
                 elif isinstance(node, PlaceholderNode):
                     return sym
+                elif isinstance(node, TypeAlias) and node.no_args:
+                    assert isinstance(node.target, ProperType)
+                    if isinstance(node.target, Instance):
+                        nextsym = node.target.type.get(part)
                 else:
                     if isinstance(node, Var):
                         typ = get_proper_type(node.type)

test-data/unit/check-literal.test

@@ -3149,3 +3149,17 @@ err_code = -TWO
 if bool():
     err_code = -THREE
 [builtins fixtures/float.pyi]
+
+[case testAliasForEnumTypeAsLiteral]
+from typing_extensions import Literal
+from enum import Enum
+
+class Foo(Enum):
+    A = 1
+
+F = Foo
+
+x: Literal[Foo.A]
+y: Literal[F.A]
+reveal_type(x)  # N: Revealed type is 'Literal[__main__.Foo.A]'
+reveal_type(y)  # N: Revealed type is 'Literal[__main__.Foo.A]'

test-data/unit/check-type-aliases.test

@@ -632,3 +632,24 @@ except E as e:
     reveal_type(e)  # N: Revealed type is '__main__.E'
 [builtins fixtures/exception.pyi]
 [out]
+
+[case testNestedClassOnAliasAsType]
+class Out:
+    class In:
+        class Inner:
+            pass
+
+O = Out
+I = Out.In
+OI = O.In
+A = Out
+B = A
+
+w: O.In
+x: I.Inner
+y: OI.Inner
+z: B.In
+reveal_type(w)  # N: Revealed type is '__main__.Out.In'
+reveal_type(x)  # N: Revealed type is '__main__.Out.In.Inner'
+reveal_type(y)  # N: Revealed type is '__main__.Out.In.Inner'
+reveal_type(z)  # N: Revealed type is '__main__.Out.In'