fix: prevent error in DateTime schema type if no widget/request set

when we use this intentionally, the widget/request should be set as
expected. but apparently this gets instantiated sometimes (by
ColanderAlchemy?) without a widget.

so this adds sane fallback logic, instead of outright error

src/wuttaweb/forms/schema.py

@@ -31,6 +31,7 @@ import colander
 import sqlalchemy as sa
 
 from wuttjamaican.conf import parse_list
+from wuttjamaican.util import localtime
 
 from wuttaweb.db import Session
 from wuttaweb.forms import widgets
@@ -38,28 +39,38 @@ from wuttaweb.forms import widgets
 
 class WuttaDateTime(colander.DateTime):
     """
-    Custom schema type for ``datetime`` fields.
+    Custom schema type for :class:`~python:datetime.datetime` fields.
 
     This should be used automatically for
-    :class:`sqlalchemy:sqlalchemy.types.DateTime` columns unless you
-    register another default.
+    :class:`~sqlalchemy:sqlalchemy.types.DateTime` ORM columns unless
+    you register another default.
 
     This schema type exists for sake of convenience, when working with
     the Buefy datepicker + timepicker widgets.
+
+    It also follows the datetime handling "rules" as outlined in
+    :doc:`wuttjamaican:narr/datetime`.  On the Python side, values
+    should be naive/UTC datetime objects.  On the HTTP side, values
+    will be ISO-format strings representing aware/local time.
     """
 
     def serialize(self, node, appstruct):
         if not appstruct:
             return colander.null
 
+        # nb. request should be present when it matters
+        if node.widget and node.widget.request:
             request = node.widget.request
             config = request.wutta_config
             app = config.get_app()
+            appstruct = app.localtime(appstruct)
+        else:
+            # but if not, fallback to config-less logic
+            appstruct = localtime(appstruct)
 
-        dt = app.localtime(appstruct)
         if self.format:
-            return dt.strftime(self.format)
-        return dt.isoformat()
+            return appstruct.strftime(self.format)
+        return appstruct.isoformat()
 
     def deserialize(  # pylint: disable=inconsistent-return-statements
         self, node, cstruct
@@ -72,6 +83,7 @@ class WuttaDateTime(colander.DateTime):
             "%Y-%m-%dT%I:%M %p",
         ]
 
+        # nb. request is always assumed to be present here
         request = node.widget.request
         config = request.wutta_config
         app = config.get_app()

tests/forms/test_schema.py

@@ -62,6 +62,13 @@ class TestWuttaDateTime(WebTestCase):
             )
             self.assertEqual(result, "2024-12-11 02:33 PM")
 
+            # missing widget/request/config
+            typ = mod.WuttaDateTime()
+            node = colander.SchemaNode(typ)
+            result = typ.serialize(node, datetime.datetime(2024, 12, 11, 22, 33))
+            # nb. not possible to know which timezone is system-local
+            self.assertTrue(result.startswith("2024-12-"))
+
     def test_deserialize(self):
         tzlocal = get_timezone_by_name("America/Los_Angeles")
         with patch.object(self.app, "get_timezone", return_value=tzlocal):