[FIX] stock_account: Return product with revaluation layer

How to reproduce:
1- Create Product Category "PC" AVCO|FIFO Automated.
2- Create Storable Product "P" with product category PC and unit cost to 1.
3- Create SO with 10 units of P.
4- Create PO with 10 units of P and unit cost of 2.
    Delivery of the SO should now have 2 IV layers, with one being "Revaluation of XXX (negative inventory)"
    Global IV of P should be 0 qty, 0 value.
5- Return the delivery order of SO.
6- Open valuation of the return

Error: The value is 0, should be 20
In `_get_price_unit`, `price_unit` is taken on the last svl of the origin_returned_move_id, in our case it's the revaluation layer.
`_get_price_unit` now take all svls of origin_returned_move_id into account.

OPW-2784033

closes odoo/odoo#85751

Signed-off-by: Arnold Moyaux <arm@odoo.com>

addons/stock_account/models/stock_move.py

@@ -39,7 +39,9 @@ class StockMove(models.Model):
         precision = self.env['decimal.precision'].precision_get('Product Price')
         # If the move is a return, use the original move's price unit.
         if self.origin_returned_move_id and self.origin_returned_move_id.sudo().stock_valuation_layer_ids:
-            return self.origin_returned_move_id.sudo().stock_valuation_layer_ids[-1].unit_cost
+            layers = self.origin_returned_move_id.sudo().stock_valuation_layer_ids
+            quantity = sum(layers.mapped("quantity"))
+            return layers.currency_id.round(sum(layers.mapped("value")) / quantity) if not float_is_zero(quantity, layers.uom_id.rounding) else 0
         return price_unit if not float_is_zero(price_unit, precision) or self._should_force_price_unit() else self.product_id.standard_price
 
     @api.model

addons/stock_account/tests/test_stockvaluationlayer.py

@@ -515,6 +515,16 @@ class TestStockValuationAVCO(TestStockValuationCommon):
         self.assertEqual(self.product1.quantity_svl, 0)
         self.assertEqual(self.product1.standard_price, 1.01)
 
+    def test_return_delivery_2(self):
+        self.product1.write({"standard_price": 1})
+        move1 = self._make_out_move(self.product1, 10, create_picking=True, force_assign=True)
+        move2 = self._make_in_move(self.product1, 10, unit_cost=2)
+        move3 = self._make_return(move1, 10)
+
+        self.assertEqual(self.product1.value_svl, 20)
+        self.assertEqual(self.product1.quantity_svl, 10)
+        self.assertEqual(self.product1.standard_price, 2)
+
 
 class TestStockValuationFIFO(TestStockValuationCommon):
     def setUp(self):
@@ -685,6 +695,15 @@ class TestStockValuationFIFO(TestStockValuationCommon):
         returned = self._make_return(out_move02, 1)
         self.assertEqual(returned.stock_valuation_layer_ids.value, 0)
 
+    def test_return_delivery_3(self):
+        self.product1.write({"standard_price": 1})
+        move1 = self._make_out_move(self.product1, 10, create_picking=True, force_assign=True)
+        move2 = self._make_in_move(self.product1, 10, unit_cost=2)
+        move3 = self._make_return(move1, 10)
+
+        self.assertEqual(self.product1.value_svl, 20)
+        self.assertEqual(self.product1.quantity_svl, 10)
+
 
 class TestStockValuationChangeCostMethod(TestStockValuationCommon):
     def test_standard_to_fifo_1(self):