fix TypeAlias stubgen

Author: makridenko

mypy/stubgen.py

@@ -920,13 +920,14 @@ def visit_assignment_stmt(self, o: AssignmentStmt) -> None:
                     continue
             if (
                 isinstance(lvalue, NameExpr)
-                and not self.is_private_name(lvalue.name)
-                # it is never an alias with explicit annotation
-                and not o.unanalyzed_type
                 and self.is_alias_expression(o.rvalue)
+                and not self.is_private_name(lvalue.name)
             ):
-                self.process_typealias(lvalue, o.rvalue)
-                continue
+                is_type_alias = o.unanalyzed_type and getattr(o.type, 'name', None) == 'TypeAlias'
+                if not o.unanalyzed_type or is_type_alias:
+                    self.process_typealias(lvalue, o.rvalue)
+                    continue
+
             if isinstance(lvalue, (TupleExpr, ListExpr)):
                 items = lvalue.items
                 if isinstance(o.unanalyzed_type, TupleType):  # type: ignore[misc]

test-data/unit/stubgen.test

@@ -1544,6 +1544,15 @@ from typing import TypeVar
 T = TypeVar('T')
 alias = Union[T, List[T]]
 
+[case testTypeAlias]
+from typing import TypeAlias
+
+alias: TypeAlias = tuple[int, str]
+
+[out]
+alias = tuple[int, str]
+
+
 [case testEllipsisAliasPreserved]
 
 alias = Tuple[int, ...]