Add handling of field names tuple to stubgen (#4407)

Fixes #4406

Author: hoefling

mypy/stubgen.py

@@ -593,7 +593,7 @@ def process_namedtuple(self, lvalue: NameExpr, rvalue: CallExpr) -> None:
         name = repr(getattr(rvalue.args[0], 'value', '<ERROR>'))
         if isinstance(rvalue.args[1], StrExpr):
             items = repr(rvalue.args[1].value)
-        elif isinstance(rvalue.args[1], ListExpr):
+        elif isinstance(rvalue.args[1], (ListExpr, TupleExpr)):
             list_items = cast(List[StrExpr], rvalue.args[1].items)
             items = '[%s]' % ', '.join(repr(item.value) for item in list_items)
         else:

test-data/unit/stubgen.test

@@ -569,6 +569,20 @@ _X = namedtuple('_X', ['a', 'b'])
 
 class Y(_X): ...
 
+[case testNamedtupleAltSyntaxFieldsTuples]
+from collections import namedtuple, x
+X = namedtuple('X', ())
+Y = namedtuple('Y', ('a',))
+Z = namedtuple('Z', ('a', 'b', 'c', 'd', 'e'))
+[out]
+from collections import namedtuple
+
+X = namedtuple('X', [])
+
+Y = namedtuple('Y', ['a'])
+
+Z = namedtuple('Z', ['a', 'b', 'c', 'd', 'e'])
+
 [case testArbitraryBaseClass]
 import x
 class D(x.C): ...