Make sure overload checks work for TypeAlias, see #1416

jedi/inference/gradual/typing.py

@@ -213,6 +213,9 @@ class TypeAlias(LazyValueWrapper):
         cls = next(iter(classes))
         return cls
 
+    def gather_annotation_classes(self):
+        return ValueSet([self._get_wrapped_value()])
+
 
 class Callable(BaseTypingValueWithGenerics):
     def py__call__(self, arguments):

test/completion/pep0484_overload.py

@@ -0,0 +1,28 @@
+# python >= 3.4
+from typing import List, Dict, overload
+
+
+# -------------------------
+# With base classes
+# -------------------------
+
+@overload
+def overload_f2(value: List) -> str: ...
+@overload
+def overload_f2(value: Dict) -> int: ...
+
+#? str()
+overload_f2([''])
+#? int()
+overload_f2({1.0: 1.0})
+
+
+@overload
+def overload_f3(value: list) -> str: ...
+@overload
+def overload_f3(value: dict) -> float: ...
+
+#? str()
+overload_f3([''])
+#? float()
+overload_f3({1.0: 1.0})