add conformance tests for namedtuple spec changes

Author: yangdanny97

conformance/tests/namedtuples_define_class.py

@@ -49,6 +49,33 @@ class Point(NamedTuple):
 p10 = Point(1, 2, "", other="")  # E
 
 
+# > Fields must be annotated attributes - methods and un-annotated attributes are not
+# > considered fields.
+
+
+class Point2(NamedTuple):
+    x: int
+    y: int
+    units = "meters"  # Not a field
+
+    def is_origin(self) -> int:  # Not a field
+        return self.x == 0 and self.y == 0
+
+
+p11 = Point2(1, 2)
+assert_type(p11, Point2)
+x, y = p11
+
+p12 = Point2(1, 2, "")  # E
+
+
+# > Field names may not start with an underscore.
+
+class Point3(NamedTuple):
+    x: int
+    _y: int  # E: illegal field name
+
+
 # > The runtime implementation of ``NamedTuple`` enforces that fields with default
 # > values must come after fields without default values. Type checkers should
 # > likewise enforce this restriction::

conformance/tests/namedtuples_define_functional.py

@@ -43,18 +43,21 @@
 p6_4 = Point6(x=1.1, y=2)  # E
 
 
-# > At runtime, the ``namedtuple`` function disallows field names that are
-# > illegal Python identifiers and either raises an exception or replaces these
-# > fields with a parameter name of the form ``_N``. The behavior depends on
-# > the value of the ``rename`` argument. Type checkers may replicate this
-# > behavior statically.
+# > At runtime, the ``namedtuple`` function disallows field names that begin with
+# > an underscore or are illegal Python identifiers, and either raises an exception
+# > or replaces these fields with a parameter name of the form ``_N``. The behavior
+# > depends on the value of the ``rename`` argument. Type checkers may replicate
+# > this behavior statically.
 
 NT1 = namedtuple("NT1", ["a", "a"])  # E?: duplicate field name
 NT2 = namedtuple("NT2", ["abc", "def"])  # E?: illegal field name
 NT3 = namedtuple("NT3", ["abc", "def"], rename=False)  # E?: illegal field name
+NT4 = namedtuple("NT4", ["abc", "_d"], rename=False)  # E?: illegal field name
 
-NT4 = namedtuple("NT4", ["abc", "def"], rename=True)  # OK
-NT4(abc="", _1="")  # OK
+NT5 = namedtuple("NT5", ["abc", "def"], rename=True)  # OK
+NT5(abc="", _1="")  # OK
+NT6 = namedtuple("NT6", ["abc", "_d"], rename=True)  # OK
+NT6(abc="", _1="")  # OK
 
 
 # > The ``namedtuple`` function also supports a ``defaults`` keyword argument that