[FIX] mail: handle non-thread model in _message_format

Calling _message_format on a anything but a thread could throw a traceback.

Task-3254379

Part-of: odoo/odoo#117763

addons/mail/models/mail_message.py

@@ -884,7 +884,8 @@ class Message(models.Model):
             if message_sudo.model and message_sudo.res_id:
                 record_sudo = self.env[message_sudo.model].browse(message_sudo.res_id).sudo()
                 record_name = record_sudo.with_prefetch(thread_ids_by_model_name[message_sudo.model]).display_name
-                default_subject = record_sudo._message_compute_subject()
+                # if not a thread, display_name is the default subject
+                default_subject = record_sudo._message_compute_subject() if hasattr(record_sudo, '_message_compute_subject') else record_name
             else:
                 record_name = False
                 default_subject = False

addons/test_mail/tests/test_mail_message.py

@@ -97,16 +97,18 @@ class TestMessageValues(MailCommon):
     @mute_logger('odoo.models.unlink')
     def test_mail_message_format(self):
         record1 = self.env['mail.test.simple'].create({'name': 'Test1'})
-        message = self.env['mail.message'].create([{
-            'model': 'mail.test.simple',
-            'res_id': record1.id,
-        }])
-        res = message.message_format()
-        self.assertEqual(res[0].get('record_name'), 'Test1')
-
-        record1.write({"name": "Test2"})
-        res = message.message_format()
-        self.assertEqual(res[0].get('record_name'), 'Test2')
+        record2 = self.env['mail.test.nothread'].create({'name': 'Test2'})
+        messages = self.env['mail.message'].create([{
+            'model': record._name,
+            'res_id': record.id,
+        } for record in [record1, record2]])
+        for message, record in zip(messages, [record1, record2]):
+            with self.subTest(record=record):
+                formatted = message.message_format()[0]
+                self.assertEqual(formatted['record_name'], record.name)
+                record.write({'name': 'Just Test'})
+                formatted = message.message_format()[0]
+                self.assertEqual(formatted['record_name'], 'Just Test')
 
     @mute_logger('odoo.models.unlink')
     def test_mail_message_format_access(self):

addons/test_mail/tests/test_mail_thread_internals.py

@@ -403,6 +403,29 @@ class TestDiscuss(MailCommon, TestRecipients):
 class TestNoThread(MailCommon, TestRecipients):
     """ Specific tests for cross models thread features """
 
+    @users('employee')
+    def test_message_format(self):
+        """ Test formatting of messages when linked to non-thread models.
+        Format could be asked notably if an inbox notification due to a
+        'message_notify' happens. """
+        test_record = self.env['mail.test.nothread'].create({
+            'customer_id': self.partner_1.id,
+            'name': 'Not A Thread',
+        })
+        message = self.env['mail.message'].create({
+            'model': test_record._name,
+            'record_name': 'Not used in message_format',
+            'res_id': test_record.id,
+        })
+        formatted = message.message_format()[0]
+        self.assertEqual(formatted['default_subject'], test_record.name)
+        self.assertEqual(formatted['record_name'], test_record.name)
+
+        test_record.write({'name': 'Just Test'})
+        formatted = message.message_format()[0]
+        self.assertEqual(formatted['default_subject'], 'Just Test')
+        self.assertEqual(formatted['record_name'], 'Just Test')
+
     @users('employee')
     def test_message_notify(self):
         """ Test notifying on non-thread models, using MailThread as an abstract