[FIX] stock: _free_reservation

to reproduce:
- have 4 units of product 1 in stock
- create a move for a dozen, reserve it
- try to scrap a single unit
- an exception "cannot reserve more than available" is raised

To reflect the change of reservation after scrapping the quantity, we
have to update the reserved quantity on the move line.
When updating the quantity on the move line, "quantity_split" is in the
quant uom, so it should be converted to the uom of the move line.

addons/stock/models/stock_move_line.py

@@ -496,7 +496,7 @@ def _free_reservation(self, product_id, location_id, quantity, lot_id=None, pack
                         candidate.product_qty - quantity,
                         precision_rounding=self.product_uom_id.rounding,
                         rounding_method='UP')
-                    candidate.product_uom_qty = self.product_id.uom_id._compute_quantity(quantity_split, self.product_uom_id, rounding_method='HALF-UP')
+                    candidate.product_uom_qty = self.product_id.uom_id._compute_quantity(quantity_split, candidate.product_uom_id, rounding_method='HALF-UP')
                     quantity -= quantity_split
                     move_to_recompute_state |= candidate.move_id
                 if quantity == 0.0:

addons/stock/tests/test_move.py

@@ -2690,6 +2690,47 @@ def test_scrap_4(self):
         scrapped_move.quantity_done = 8
         self.assertEqual(scrap.scrap_qty, 8, 'Scrap quantity is not updated.')
 
+    def test_scrap_5(self):
+        """ Scrap the product of a reserved move line where the product is reserved in another
+        unit of measure. Check that the move line is correctly updated after the scrap.
+        """
+        # 4 units are available in stock
+        self.env['stock.quant']._update_available_quantity(self.product1, self.stock_location, 4)
+
+        # try to reserve a dozen
+        partner = self.env['res.partner'].create({'name': 'Kimberley'})
+        picking = self.env['stock.picking'].create({
+            'name': 'A single picking with one move to scrap',
+            'location_id': self.stock_location.id,
+            'location_dest_id': self.customer_location.id,
+            'partner_id': partner.id,
+            'picking_type_id': self.env.ref('stock.picking_type_out').id,
+        })
+        move1 = self.env['stock.move'].create({
+            'name': 'A move to confirm and scrap its product',
+            'location_id': self.stock_location.id,
+            'location_dest_id': self.customer_location.id,
+            'product_id': self.product1.id,
+            'product_uom': self.uom_dozen.id,
+            'product_uom_qty': 1.0,
+            'picking_id': picking.id,
+        })
+        move1._action_confirm()
+        move1._action_assign()
+        self.assertEqual(move1.reserved_availability, 0.33)
+
+        # scrap a unit
+        scrap = self.env['stock.scrap'].create({
+            'product_id': self.product1.id,
+            'product_uom_id': self.product1.uom_id.id,
+            'scrap_qty': 1,
+            'picking_id': picking.id,
+        })
+        scrap.action_validate()
+
+        self.assertEqual(scrap.state, 'done')
+        self.assertEqual(move1.reserved_availability, 0.25)
+
     def test_in_date_1(self):
         """ Check that moving a tracked quant keeps the incoming date.
         """