[FIX] stock: keep previously set result package in pickings

Steps to reproduce:

* In Inventory, activate multiple warehouses and storage locations, multi-step routes, Delivery packages
* On the main warehouse, activate 3 steps delivery
* Create a stockable product A
* Update quantity on hand: 100 units in a package PACK1 in Stock/Shelf 1
* Create a new Pick transfer with one move: 120 product A
* Set the transfer as todo and check availability: a move line for the 100 units from PACK1 is created
* Edit the move line: set a destination location, **change the result package to PACK2** and set a qty_done
* On product A, update the quantity on hand: add a *new* package PACK3 of 20 in Stock/Shelf 1
* On the transfer, click on check availability

Current behavior:

* A new move line is created for the 20 units from PACK3 to PACK3: ok
* The move line edited before for the 100 units has its result package **reset to PACK1**

Expected behavior:

* A new move line is created for the 20 units from PACK3 to PACK3: ok
* The move line edited before for the 100 units has its result package kept to **PACK2 as edited by the user** who decided to open the package already

Short analysis:

At the end of `StockMove._action_assign()`, the method `StockPicking._check_entire_pack()` is called. For each package moved by a move line, this method checks if the package is entirely moved (sum of quants == sum of move lines). The check is done by `StockPicking._check_move_lines_map_quant_package`. When the sums match, the package level of the move lines is created or updated. When it happens, it writes the package in the `result_package_id` of the related lines.

It should not change the result_package_id if it was already set.

Thinking further, maybe it should not consider lines with a `qty_done` in `_check_move_lines_map_quant_package`: users already picked these lines, if they decided to empty or change the `result_package_id`, a new check of availability for the remaining quantities should not change these lines.

opw-2346608
Fixes #58491

closes odoo/odoo#60025

X-original-commit: db262912eb716aed1c42be8a9d59c25bdfa400e0
Signed-off-by: Nicolas Martinelli (nim) <nim@odoo.com>

addons/stock/models/stock_picking.py

@@ -833,7 +833,7 @@ class Picking(models.Model):
             for pack in origin_packages:
                 if picking._check_move_lines_map_quant_package(pack):
                     package_level_ids = picking.package_level_ids.filtered(lambda pl: pl.package_id == pack)
-                    move_lines_to_pack = picking.move_line_ids.filtered(lambda ml: ml.package_id == pack)
+                    move_lines_to_pack = picking.move_line_ids.filtered(lambda ml: ml.package_id == pack and not ml.result_package_id)
                     if not package_level_ids:
                         self.env['stock.package_level'].create({
                             'picking_id': picking.id,

addons/stock/tests/test_packing.py

@@ -666,3 +666,67 @@ class TestPacking(TestPackingCommon):
 
         pick_picking.move_line_ids.qty_done = 3
         first_pack = pick_picking.action_put_in_pack()
+
+    def test_action_assign_package_level(self):
+        """calling _action_assign on move does not erase lines' "result_package_id"
+        At the end of the method ``StockMove._action_assign()``, the method
+        ``StockPicking._check_entire_pack()`` is called. This method compares
+        the move lines with the quants of their source package, and if the entire
+        package is moved at once in the same transfer, a ``stock.package_level`` is
+        created. On creation of a ``stock.package_level``, the result package of
+        the move lines is directly updated with the entire package.
+        This is good on the first assign of the move, but when we call assign for
+        the second time on a move, for instance because it was made partially available
+        and we want to assign the remaining, it can override the result package we
+        selected before.
+        An override of ``StockPicking._check_move_lines_map_quant_package()`` ensures
+        that we ignore:
+        * picked lines (qty_done > 0)
+        * lines with a different result package already
+        """
+        package = self.env["stock.quant.package"].create({"name": "Src Pack"})
+        dest_package1 = self.env["stock.quant.package"].create({"name": "Dest Pack1"})
+
+        # Create new picking: 120 productA
+        picking_form = Form(self.env['stock.picking'])
+        picking_form.picking_type_id = self.warehouse.pick_type_id
+        with picking_form.move_ids_without_package.new() as move_line:
+            move_line.product_id = self.productA
+            move_line.product_uom_qty = 120
+        picking = picking_form.save()
+
+        # mark as TO-DO
+        picking.action_confirm()
+
+        # Update quantity on hand: 100 units in package
+        self.env['stock.quant']._update_available_quantity(self.productA, self.stock_location, 100, package_id=package)
+
+        # Check Availability
+        picking.action_assign()
+
+        self.assertEqual(picking.state, "assigned")
+        self.assertEqual(picking.package_level_ids.package_id, package)
+
+        move = picking.move_lines
+        line = move.move_line_ids
+
+        # change the result package and set a qty_done
+        line.qty_done = 100
+        line.result_package_id = dest_package1
+
+        # Update quantity on hand: 20 units in new_package
+        new_package = self.env["stock.quant.package"].create({"name": "New Pack"})
+        self.env['stock.quant']._update_available_quantity(self.productA, self.stock_location, 20, package_id=new_package)
+
+        # Check Availability
+        picking.action_assign()
+
+        # Check that result package is not changed on first line
+        new_line = move.move_line_ids - line
+        self.assertRecordValues(
+            line + new_line,
+            [
+                {"qty_done": 100, "result_package_id": dest_package1.id},
+                {"qty_done": 0, "result_package_id": new_package.id},
+            ],
+        )