[FIX] base_automation: warn email are not compatible with unlink

Create a automated action on deletion that send an email, delete a
related record. The email is not sent.

Email are linked to their chatter message, when the later is deleted the
former is deleted in cascade too. This is a known limitation of the mail
model.

closes odoo/odoo#62616

Task: 2151519
X-original-commit: f8904eb19d82d1d255c1ef091d1e47e0e016a62f
Signed-off-by: Julien Castiaux <Julien00859@users.noreply.github.com>
Signed-off-by: Raphael Collet (rco) <rco@openerp.com>

addons/base_automation/models/base_automation.py

@@ -107,6 +107,16 @@ class BaseAutomation(models.Model):
                 }
             }}
 
+        MAIL_STATES = ('email', 'followers', 'next_activity')
+        if self.trigger == 'on_unlink' and self.state in MAIL_STATES:
+            return {'warning': {
+                'title': _("Warning"),
+                'message': _(
+                    "You cannot send an email, add followers or create an activity "
+                    "for a deleted record.  It simply does not work."
+                ),
+            }}
+
     @api.model_create_multi
     def create(self, vals_list):
         for vals in vals_list: