[FIX] mrp: change qty_producing when updating product_qty

Currently, when no workorders are defined for a production, updating its
`product_qty` through the wizard won't update its qty_producing, meaning
that if the production gets validated right afterwards, the total
produced will be the same as prior the update.

This is missleading and unconsistent with how things work when
workorders are involved, since in that case the `qty_producing` of the
production will be updated through the inverse of the workorder's
`qty_producing`.

Part-of: odoo#129009

addons/mrp/tests/test_order.py

@@ -296,20 +296,26 @@ def test_update_quantity_2(self):
         mo_form.qty_producing = 2
         mo = mo_form.save()
 
-        mo._post_inventory()
+        # Produce & backorder
+        action = mo.button_mark_done()
+        backorder = Form(self.env['mrp.production.backorder'].with_context(**action['context']))
+        backorder.save().action_backorder()
+        mo_backorder = mo.procurement_group_id.mrp_production_ids[-1]
+        self.assertEqual(mo_backorder.product_qty, 1)
 
         update_quantity_wizard = self.env['change.production.qty'].create({
-            'mo_id': mo.id,
-            'product_qty': 5,
+            'mo_id': mo_backorder.id,
+            'product_qty': 3,
         })
         update_quantity_wizard.change_prod_qty()
-        mo_form = Form(mo)
-        mo_form.qty_producing = 5
-        mo = mo_form.save()
-        mo.button_mark_done()
-
-        self.assertEqual(sum(mo.move_raw_ids.filtered(lambda m: m.product_id == p1).mapped('quantity_done')), 20)
-        self.assertEqual(sum(mo.move_finished_ids.mapped('quantity_done')), 5)
+        mo_back_form = Form(mo_backorder)
+        mo_back_form.qty_producing = 3
+        mo_backorder = mo_back_form.save()
+        mo_backorder.button_mark_done()
+
+        productions = mo | mo_backorder
+        self.assertEqual(sum(productions.move_raw_ids.filtered(lambda m: m.product_id == p1).mapped('quantity_done')), 20)
+        self.assertEqual(sum(productions.move_finished_ids.mapped('quantity_done')), 5)
 
     def test_update_quantity_3(self):
         bom = self.env['mrp.bom'].create({

addons/mrp/wizard/change_production_qty.py

@@ -3,7 +3,7 @@
 
 from odoo import api, fields, models, _
 from odoo.exceptions import UserError
-from odoo.tools import float_is_zero, float_round
+from odoo.tools import float_is_zero
 
 
 class ChangeProductionQty(models.TransientModel):
@@ -71,10 +71,8 @@ def change_prod_qty(self):
                 ))
             old_production_qty = production.product_qty
             new_production_qty = wizard.product_qty
-            done_moves = production.move_finished_ids.filtered(lambda x: x.state == 'done' and x.product_id == production.product_id)
-            qty_produced = production.product_id.uom_id._compute_quantity(sum(done_moves.mapped('product_qty')), production.product_uom_id)
 
-            factor = (new_production_qty - qty_produced) / (old_production_qty - qty_produced)
+            factor = new_production_qty / old_production_qty
             update_info = production._update_raw_moves(factor)
             documents = {}
             for move, old_qty, new_qty in update_info:
@@ -87,8 +85,12 @@ def change_prod_qty(self):
                         else:
                             documents[key] = [value]
             production._log_manufacture_exception(documents)
-            self._update_finished_moves(production, new_production_qty - qty_produced, old_production_qty - qty_produced)
+            self._update_finished_moves(production, new_production_qty, old_production_qty)
             production.write({'product_qty': new_production_qty})
+            if not float_is_zero(production.qty_producing, precision_rounding=production.product_uom_id.rounding) and\
+               not production.workorder_ids:
+                production.qty_producing = new_production_qty
+                production._set_qty_producing()
 
             for wo in production.workorder_ids:
                 operation = wo.operation_id