Fix PEP 585 type aliases in stubs

Fixes python#11859

Author: hauntsaninja

mypy/semanal.py

@@ -4085,6 +4085,7 @@ def analyze_type_application(self, expr: IndexExpr) -> None:
                 name = target.type.fullname
                 if (alias.no_args and  # this avoids bogus errors for already reported aliases
                         name in get_nongen_builtins(self.options.python_version) and
+                        not self.is_stub_file and
                         not alias.normalized):
                     self.fail(no_subscript_builtin_alias(name, propose_alt=False), expr)
         # ...or directly.

test-data/unit/check-generic-alias.test

@@ -285,3 +285,14 @@ class C(list[int]):
     pass
 d: type[str]
 [builtins fixtures/list.pyi]
+
+
+[case testTypeAliasWithBuiltinListAliasInStub]
+# flags: --python-version 3.6
+import m
+reveal_type(m.a()[0])  # N: Revealed type is "builtins.int*"
+
+[file m.pyi]
+List = list
+a = List[int]
+[builtins fixtures/list.pyi]