[FIX] mail: followers alias check on models not inheriting from alias mixin

You could try to check followers on a model not inheriting from mail alias
mixin. In that case current code would check followers on a void mail
alias mixin record, meaning no followers found. Instead we now
differentiate the class method from the method checking record properties.

addons/hr/models/mail_alias.py

@@ -13,8 +13,8 @@ class Alias(models.Model):
 class MailAlias(models.AbstractModel):
     _inherit = 'mail.alias.mixin'
 
-    def _alias_check_contact(self, message, message_dict, alias):
-        if alias.alias_contact == 'employees' and self.ids:
+    def _alias_check_contact_on_record(self, record, message, message_dict, alias):
+        if alias.alias_contact == 'employees' and record.ids:
             email_from = tools.decode_message_header(message, 'From')
             email_address = tools.email_split(email_from)[0]
             employee = self.env['hr.employee'].search([('work_email', 'ilike', email_address)], limit=1)
@@ -26,4 +26,4 @@ class MailAlias(models.AbstractModel):
                     'error_template': self.env.ref('hr.mail_template_data_unknown_employee_email_address').body_html,
                 }
             return True
-        return super(MailAlias, self)._alias_check_contact(message, message_dict, alias)
+        return super(MailAlias, self)._alias_check_contact_on_record(record, message, message_dict, alias)

addons/mail/models/mail_alias.py

@@ -264,13 +264,24 @@ class AliasMixin(models.AbstractModel):
                          record._name, record.display_name, record.id)
 
     def _alias_check_contact(self, message, message_dict, alias):
+        """ Main mixin method that inheriting models may inherit in order
+        to implement a specifc behavior. """
+        return self._alias_check_contact_on_record(self, message, message_dict, alias)
+
+    def _alias_check_contact_on_record(self, record, message, message_dict, alias):
+        """ Generic method that takes a record not necessarily inheriting from
+        mail.alias.mixin. """
         author = self.env['res.partner'].browse(message_dict.get('author_id', False))
-        if alias.alias_contact == 'followers' and self.ids:
-            if not hasattr(self, "message_partner_ids") or not hasattr(self, "message_channel_ids"):
+        if alias.alias_contact == 'followers':
+            if not record.ids:
+                return {
+                    'error_message': _('incorrectly configured alias (unknown reference record)'),
+                }
+            if not hasattr(record, "message_partner_ids") or not hasattr(record, "message_channel_ids"):
                 return {
                     'error_message': _('incorrectly configured alias'),
                 }
-            accepted_partner_ids = self.message_partner_ids | self.message_channel_ids.mapped('channel_partner_ids')
+            accepted_partner_ids = record.message_partner_ids | record.message_channel_ids.mapped('channel_partner_ids')
             if not author or author not in accepted_partner_ids:
                 return {
                     'error_message': _('restricted to followers'),

addons/mail/models/mail_thread.py

@@ -956,9 +956,10 @@ class MailThread(models.AbstractModel):
                 obj = self.env[alias.alias_parent_model_id.model].browse(alias.alias_parent_thread_id)
             elif model:
                 obj = self.env[model]
-            if not hasattr(obj, '_alias_check_contact'):
-                obj = self.env['mail.alias.mixin']
-            check_result = obj._alias_check_contact(message, message_dict, alias)
+            if hasattr(obj, '_alias_check_contact'):
+                check_result = obj._alias_check_contact(message, message_dict, alias)
+            else:
+                check_result = self.env['mail.alias.mixin']._alias_check_contact_on_record(obj, message, message_dict, alias)
             if check_result is not True:
                 self._routing_warn(_('alias %s: %s') % (alias.alias_name, check_result.get('error_message', _('unknown error'))), _('skipping'), message_id, route, False)
                 self._routing_create_bounce_email(email_from, check_result.get('error_template', _generic_bounce_body_html), message)