DEPR: Deprecate NaT.to_datetime

Closes gh-8254.

Author: gfyoung

pandas/tseries/tests/test_timeseries.py

@@ -1020,7 +1020,13 @@ def test_NaT_methods(self):
 
         for method in nat_methods:
             if hasattr(NaT, method):
-                self.assertIs(getattr(NaT, method)(), NaT)
+                # see gh-8254
+                exp_warning = None
+                if method == 'to_datetime':
+                    exp_warning = FutureWarning
+                with tm.assert_produces_warning(
+                        exp_warning, check_stacklevel=False):
+                    self.assertIs(getattr(NaT, method)(), NaT)
 
         # GH 12300
         self.assertEqual(NaT.isoformat(), 'NaT')

pandas/tslib.pyx

@@ -791,11 +791,11 @@ def _make_nan_func(func_name):
     f.__name__ = func_name
     return f
 
-_nat_methods = ['date', 'now', 'replace', 'to_datetime', 'today']
+_nat_methods = ['date', 'now', 'replace', 'to_pydatetime', 'today']
 
 _nan_methods = ['weekday', 'isoweekday', 'total_seconds']
 
-_implemented_methods = ['to_datetime64', 'isoformat']
+_implemented_methods = ['to_datetime', 'to_datetime64', 'isoformat']
 _implemented_methods.extend(_nat_methods)
 _implemented_methods.extend(_nan_methods)