jsonifier: fix date handling

We should always keep UTC and let the consumer deal w/ it.
This change is backward compatible but allows to turn off
the old behavior w/ the ctx flag `jsonifier__date_user_tz=False`.

jsonifier/models/models.py

@@ -49,9 +49,10 @@ class Base(models.AbstractModel):
         elif field.type == "datetime":
             # Ensures value is a datetime
             value = fields.Datetime.to_datetime(value)
-            # Get the timestamp converted to the client's timezone.
-            # This call also add the tzinfo into the datetime object
-            value = fields.Datetime.context_timestamp(self, value)
+            if self.env.context.get("jsonifier__date_user_tz"):
+                # Get the timestamp converted to the client's timezone.
+                # This call also add the tzinfo into the datetime object
+                value = fields.Datetime.context_timestamp(self, value)
             value = value.isoformat()
         elif field.type in ("many2one", "reference"):
             value = value.display_name if value else None
@@ -162,9 +163,16 @@ class Base(models.AbstractModel):
 
         results = [{} for record in self]
         parsers = {False: parser["fields"]} if "fields" in parser else parser["langs"]
+        records = self
+        if "jsonifier__date_user_tz" not in self.env.context:
+            # TODO: backward compat flag for v < 15.0
+            # Dates must always be UTC and the client/consumer of this data
+            # should deal w/ the format as preferred.
+            # Drop this flag for v15!
+            records = records.with_context(jsonifier__date_user_tz=True)
         for lang in parsers:
             translate = lang or parser.get("language_agnostic")
-            records = self.with_context(lang=lang) if translate else self
+            records = records.with_context(lang=lang) if translate else records
             for record, json in zip(records, results):
                 self._jsonify_record(parsers[lang], record, json)