[FIX] website_slides: do not crash when deleting a slide

Steps to reproduce:

- Install the elearning module and go to a course not created by you.
- Try to delete or add any slide.
Note: the bug is not consistent it might happen for some courses and not
for others.

Issue: We get a traceback error when trying to modify anything about the
slides in this course.

Solution:
Adding the `'channel_id.slide_ids.slide_ids'` dependece to the
`_compute_category_id` will make the computation to take into account
the changes on the slides.

opw-3316697

closes odoo/odoo#128022

X-original-commit: 1d6f8f4c606ddb7f57acd7ef2a9f983d7de84a34
Signed-off-by: Thibault Delavallee (tde) <tde@openerp.com>

addons/website_slides/models/slide_slide.py

@@ -259,7 +259,7 @@ class Slide(models.Model):
     def _get_placeholder_filename(self, field):
         return self.channel_id._get_placeholder_filename(field)
 
-    @api.depends('channel_id.slide_ids.is_category', 'channel_id.slide_ids.sequence')
+    @api.depends('channel_id.slide_ids.is_category', 'channel_id.slide_ids.sequence', 'channel_id.slide_ids.slide_ids')
     def _compute_category_id(self):
         """ Will take all the slides of the channel for which the index is higher
         than the index of this category and lower than the index of the next category.

addons/website_slides/tests/test_slide_slide.py

@@ -9,6 +9,42 @@ from odoo.tools import mute_logger
 
 
 class TestSlideInternals(slides_common.SlidesCase):
+    def test_compute_category_completion_time(self):
+        """
+            Check that we properly calculate the completion time of a course without error, after deleting a slide.
+        """
+        self.category2 = self.env['slide.slide'].with_user(self.user_officer).create({
+            'name': 'Cooking Tips For Dieting',
+            'channel_id': self.channel.id,
+            'is_category': True,
+            'is_published': True,
+            'sequence': 5,
+        })
+        self.slide_4 = self.env['slide.slide'].with_user(self.user_officer).create({
+            'name': 'Vegan Diet',
+            'channel_id': self.channel.id,
+            'slide_category': 'document',
+            'is_published': True,
+            'completion_time': 5.0,
+            'sequence': 6,
+        })
+        self.slide_5 = self.env['slide.slide'].with_user(self.user_officer).create({
+            'name': 'Normal Diet',
+            'channel_id': self.channel.id,
+            'slide_category': 'document',
+            'is_published': True,
+            'completion_time': 1.5,
+            'sequence': 7,
+        })
+
+        before_unlink = self.category2.completion_time
+        self.assertEqual(before_unlink, self.slide_4.completion_time + self.slide_5.completion_time)
+
+        self.channel.slide_ids[6].sudo().unlink()
+        self.category2._compute_category_completion_time()
+
+        after_unlink = self.category2.completion_time
+        self.assertEqual(after_unlink, self.slide_4.completion_time)
 
     @mute_logger('odoo.sql_db')
     @users('user_manager')