[FIX][IMP] mail: make tracking great again

When changing tracking mecanism in v9 'always' tracked fields lost their meaning.
They were managed like 'onchange' fields. This commit sets the old behavior back.

 * 'onchange' fields are displayed in tracking every time they change
 * 'always' fields are displayed in tracking every time they change or whenever
   other tracking exist; those are used to display some contextual
   information

addons/mail/models/mail_thread.py

@@ -441,11 +441,14 @@ class MailThread(models.AbstractModel):
          - a set of updated column names
          - a list of changes (initial value, new value, column name, column info) """
         self.ensure_one()
-        changes = set()
+        changes = set()  # contains always and onchange tracked fields that changed
+        displays = set()  # contains always tracked field that did not change but displayed for information
         tracking_value_ids = []
+        display_values_ids = []
 
         # generate tracked_values data structure: {'col_name': {col_info, new_value, old_value}}
         for col_name, col_info in tracked_fields.items():
+            track_visibility = getattr(self._fields[col_name], 'track_visibility', 'onchange')
             initial_value = initial[col_name]
             new_value = getattr(self, col_name)
 
@@ -456,6 +459,16 @@ class MailThread(models.AbstractModel):
 
                 if col_name in tracked_fields:
                     changes.add(col_name)
+            # 'always' tracked fields in separate variable; added if other changes
+            elif new_value == initial_value and track_visibility == 'always' and col_name in tracked_fields:
+                tracking = self.env['mail.tracking.value'].create_tracking_values(initial_value, initial_value, col_name, col_info)
+                if tracking:
+                    display_values_ids.append([0, 0, tracking])
+                    displays.add(col_name)
+
+        if changes and displays:
+            tracking_value_ids = display_values_ids + tracking_value_ids
+
         return changes, tracking_value_ids
 
     @api.multi

addons/mail/models/mail_tracking_value.py

@@ -10,6 +10,7 @@ class MailTracking(models.Model):
     _name = 'mail.tracking.value'
     _description = 'Mail Tracking Value'
 
+    # TDE CLEANME: why not a m2o to ir model field ?
     field = fields.Char('Changed Field', required=True, readonly=1)
     field_desc = fields.Char('Field Description', required=True, readonly=1)
     field_type = fields.Char('Field Type')

addons/mail/static/src/xml/thread.xml

@@ -154,9 +154,11 @@
                     <t t-esc="value.changed_field"/>:
                     <t t-if="value.old_value">
                         <span> <t t-esc="value.old_value || ((value.field_type !== 'boolean') and '')"/> </span>
-                        <span class="fa fa-long-arrow-right"/>
+                        <span t-if="value.old_value != value.new_value" class="fa fa-long-arrow-right"/>
                     </t>
-                    <span> <t t-esc="value.new_value || ((value.field_type !== 'boolean') and '')"/> </span>
+                    <span t-if="value.old_value != value.new_value">
+                        <t t-esc="value.new_value || ((value.field_type !== 'boolean') and '')"/>
+                    </span>
                 </li>
             </t>
         </ul>

addons/mail/tests/test_message_track.py

@@ -122,10 +122,10 @@ class TestTracking(TestMail):
         self.assertEqual(len(self.group_pigs.message_ids), 3)
         last_msg = self.group_pigs.message_ids[0]
         self.assertEqual(last_msg.subtype_id, mt_group_public_set)
-        self.assertEqual(len(last_msg.tracking_value_ids), 2)
-        self.assertEqual(set(last_msg.tracking_value_ids.mapped('field')), set(['group_public_id', 'public']))
-        self.assertEqual(set(last_msg.tracking_value_ids.mapped('field_desc')), set(['Authorized Group', 'Privacy']))
-        self.assertEqual(set(last_msg.tracking_value_ids.mapped('old_value_char')), set([group_user.name_get()[0][1], 'Invited people only']))
-        self.assertEqual(set(last_msg.tracking_value_ids.mapped('new_value_char')), set([group_system.name_get()[0][1], 'Everyone']))
+        self.assertEqual(len(last_msg.tracking_value_ids), 3)
+        self.assertEqual(set(last_msg.tracking_value_ids.mapped('field')), set(['group_public_id', 'public', 'name']))
+        self.assertEqual(set(last_msg.tracking_value_ids.mapped('field_desc')), set(['Authorized Group', 'Privacy', 'Name']))
+        self.assertEqual(set(last_msg.tracking_value_ids.mapped('old_value_char')), set([group_user.name_get()[0][1], 'Invited people only', 'supername']))
+        self.assertEqual(set(last_msg.tracking_value_ids.mapped('new_value_char')), set([group_system.name_get()[0][1], 'Everyone', 'supername']))
         self.assertEqual(set(last_msg.tracking_value_ids.mapped('old_value_integer')), set([0, group_user.id]))
         self.assertEqual(set(last_msg.tracking_value_ids.mapped('new_value_integer')), set([0, group_system.id]))