[IMP] mail, various: send email to assigned people

When a user is assigned to a model on a user_id field an email is sent to him
containing a link to the document. This way the user is warned he is now
responsible of the task / issue / lead / ...

addons/mail/models/mail_thread.py

@@ -2004,10 +2004,17 @@ class MailThread(models.AbstractModel):
         """
         if not partner_ids:
             return
-        for record_id in self.ids:
+        for record in self:
+            record.message_post_with_view(
+                'mail.message_user_assigned',
+                composition_mode='mass_mail',
+                partner_ids=[(4, pid) for pid in partner_ids],
+                auto_delete=True,
+                auto_delete_message=True,
+                subtype_id=self.env.ref('mail.mt_note').id)
             messages = self.env['mail.message'].sudo().search([
                 ('model', '=', self._name),
-                ('res_id', '=', record_id),
+                ('res_id', '=', record.id),
                 ('subtype_id', '!=', False),
                 ('subtype_id.internal', '=', False)], limit=1)
             if messages:

addons/mail/views/mail_templates.xml

@@ -38,5 +38,17 @@
             </p>
         </template>
 
+        <template id="message_user_assigned">
+            <p>Dear <t t-esc="object.user_id.name"/>,</p>
+            <p>You have been assigned to the <t t-esc="object._description.lower()"/> <t t-esc="object.name_get()[0][1]"/>.</p>
+            <p>
+                <a t-att-href="'/mail/view?model=%s&amp;res_id=%s' % (object._name, object.id)"
+                        style="background-color: #9E588B; margin-top: 10px; padding: 10px; text-decoration: none; color: #fff; border-radius: 5px; font-size: 16px;">
+                    View <t t-esc="object._description.lower()"/>
+                </a>
+            </p>
+            <p style="color:#9E588B;">Powered by <a href="https://www.odoo.com">Odoo</a>.</p>
+        </template>
+
     </data>
 </odoo>