[FIX] purchase: picking list

When a product is returned after receiving, the return picking doesn't
appear in the corresponding PO.

opw-686895

addons/purchase/purchase.py

@@ -77,12 +77,15 @@ class PurchaseOrder(models.Model):
             types = type_obj.search([('code', '=', 'incoming'), ('warehouse_id', '=', False)])
         return types[:1]
 
-    @api.depends('order_line.move_ids.picking_id')
+    @api.depends('order_line.move_ids')
     def _compute_picking(self):
         for order in self:
             pickings = self.env['stock.picking']
             for line in order.order_line:
-                moves = line.move_ids.filtered(lambda r: r.state != 'cancel')
+                # We keep a limited scope on purpose. Ideally, we should also use move_orig_ids and
+                # do some recursive search, but that could be prohibitive if not done correctly.
+                moves = line.move_ids | line.move_ids.mapped('returned_move_ids')
+                moves = moves.filtered(lambda r: r.state != 'cancel')
                 pickings |= moves.mapped('picking_id')
             order.picking_ids = pickings
             order.picking_count = len(pickings)