[FIX] sale: SO amendments after invoicing change the unit price

Steps to reproduce:

1- install sale, invoicing
2- create a product p with price pr
3- create a new Sales Order SO with p and edit the price
to any other price than pr
4-  create an invoice
5- go to SO, reduce quantity to 0 ( customer returns the item )
6- the unit price is set back to pr and there is no way to edit it

Bug:

in 836f463c97 the `_compute_price_unit`
method was changed from onchange to depends which caused the edits now
to be commited to memory.
While it can be beneficial for other flows, for this specific use case,
it is not

Fix:
make an exception for lines with already invoiced quantities

OPW-2830824

closes odoo/odoo#94482

X-original-commit: b77346926f634f2f06fe1b06b68835a360ae91c5
Signed-off-by: Mohamed Megahed Abbas Megahed SALLAM (mome) <mome@odoo.com>

addons/sale/models/sale_order_line.py

@@ -388,6 +388,10 @@ class SaleOrderLine(models.Model):
     @api.depends('product_id', 'product_uom', 'product_uom_qty')
     def _compute_price_unit(self):
         for line in self:
+            # check if there is already invoiced amount. if so, the price shouldn't change as it might have been
+            # manually edited
+            if line.qty_invoiced > 0:
+                continue
             if not line.product_uom or not line.product_id or not line.order_id.pricelist_id:
                 line.price_unit = 0.0
             else:

addons/sale/tests/test_sale_to_invoice.py

@@ -475,3 +475,29 @@ class TestSaleToInvoice(TestSaleCommon):
 
         aml = self.env['account.move.line'].search([('move_id', 'in', so.invoice_ids.ids)])[0]
         self.assertRecordValues(aml, [{'analytic_account_id': analytic_account_so.id}])
+
+    def test_invoice_after_product_return_price_not_default(self):
+        so = self.env['sale.order'].create({
+            'name': 'Sale order',
+            'partner_id': self.partner_a.id,
+            'partner_invoice_id': self.partner_a.id,
+            'order_line': [
+                (0, 0, {'name': self.product_a.name, 'product_id': self.product_a.id, 'product_uom_qty': 1, 'price_unit': 123}),
+            ]
+        })
+        self._check_order_search(so, [('invoice_ids', '=', False)], so)
+        so.action_confirm()
+        so_context = {
+            'active_model': 'sale.order',
+            'active_ids': [so.id],
+            'active_id': so.id,
+            'default_journal_id': self.company_data['default_journal_sale'].id,
+        }
+        invoicing_wizard = self.env['sale.advance.payment.inv'].with_context(so_context).create({})
+        invoicing_wizard.create_invoices()
+        self.assertTrue(so.invoice_ids, "The invoice was not created")
+        # simulating return by changing product_uom_qty to 0
+        so.order_line.product_uom_qty = 0
+        # checking if the price_unit is the same
+        self.assertEqual(so.order_line.price_unit, 123,
+                         "The unit price should be the same as the one used to create the sales order line")