Add test for the weird NamedTuple behavior

Author: tmke8

mypy/semanal_namedtuple.py

@@ -658,14 +658,14 @@ def save_namedtuple_body(self, named_tuple_info: TypeInfo) -> Iterator[None]:
                     # Keep user-defined methods as is.
                     continue
                 elif isinstance(sym.node, Var):
-                    # NamedTuple fields are initialized in the generated __init__.
+                    # Don't track the initialization status of the mangled attributes.
                     sym.node.is_uninitialized = False
                 # Keep existing (user-provided) definitions under mangled names, so they
                 # get semantically analyzed.
                 r_key = get_unique_redefinition_name(key, named_tuple_info.names)
                 named_tuple_info.names[r_key] = sym
             if isinstance(value.node, Var):
-                # NamedTuple fields are initialized in the generated __init__.
+                # When a NamedTuple is analyzed multiple times, we have to reset this again.
                 value.node.is_uninitialized = False
             named_tuple_info.names[key] = value
 

test-data/unit/check-warnings.test

@@ -375,6 +375,17 @@ class Employee(NamedTuple):
 Employee("foo")
 [builtins fixtures/tuple.pyi]
 
+[case testUninitializedAttributeNamedTupleRunTwice]
+# flags: --warn-uninitialized-attributes
+from typing import NamedTuple
+
+NT: "N"  # Force mypy to analyze this twice.
+class N(NamedTuple):
+    x: int
+
+NT = N(1)
+[builtins fixtures/tuple.pyi]
+
 [case testUninitializedAttributeTypedDict]
 # flags: --warn-uninitialized-attributes
 from mypy_extensions import TypedDict