[FIX] purchase_stock: small discount at invoicing

- Create stockable product P: FIFO, Automated Valuation
- Set the price difference account
- Configure Decimal Accuracy for Discounts to 5.
- Create a PO
- Add a line with:
  Product P
  Quantity: 10,000
  Price unit: 100
  A tax
- Confirm the PO, receive the product and create the invoice
- Set a discount of 0.92431 on the invoice line
- Post the invoice

The journal entries for the invoices contains the price difference move,
the amount must be 9,243.10 but is 9,200.00.

In case taxes are defined on the the invoice line, we call `compute_all`
which will round the `price_unit`. In this case, we don't want to round
it.

Fixes odoo#56832
opw-2329028

X-original-commit: 498238f

Author: nim-odoo

addons/purchase_stock/models/account_invoice.py

@@ -115,8 +115,15 @@ def _stock_account_prepare_anglo_saxon_in_lines_vals(self):
 
                 price_unit = line.price_unit * (1 - (line.discount or 0.0) / 100.0)
                 if line.tax_ids:
-                    price_unit = line.tax_ids.compute_all(
+                    # We do not want to round the price unit since :
+                    # - It does not follow the currency precision
+                    # - It may include a discount
+                    # Since compute_all still rounds the total, we use an ugly workaround:
+                    # multiply then divide the price unit.
+                    price_unit *= line.quantity
+                    price_unit = line.tax_ids.with_context(round=False).compute_all(
                         price_unit, currency=move.currency_id, quantity=1.0, is_refund=move.move_type == 'in_refund')['total_excluded']
+                    price_unit /= line.quantity
 
                 if float_compare(valuation_price_unit, price_unit, precision_digits=invoice_cur_prec) != 0 \
                         and float_compare(line['price_unit'], line.price_unit, precision_digits=invoice_cur_prec) == 0:

addons/purchase_stock/tests/test_anglo_saxon_valuation_reconciliation.py

@@ -29,7 +29,7 @@ def setup_company_data(cls, company_name, chart_template=None, **kwargs):
         })
         return company_data
 
-    def _create_purchase(self, product, date, quantity=1.0):
+    def _create_purchase(self, product, date, quantity=1.0, set_tax=False):
         rslt = self.env['purchase.order'].create({
             'partner_id': self.partner_a.id,
             'currency_id': self.currency_data['currency'].id,
@@ -41,6 +41,7 @@ def _create_purchase(self, product, date, quantity=1.0):
                     'product_uom': product.uom_po_id.id,
                     'price_unit': 66.0,
                     'date_planned': date,
+                    'taxes_id': [(6, 0, product.supplier_taxes_id.ids)] if set_tax else False,
                 })],
              'date_order': date,
         })
@@ -146,3 +147,38 @@ def test_multiple_shipments_invoices(self):
         self._process_pickings(purchase_order.picking_ids.filtered(lambda x: x.state != 'done'), quantity=3.0)
         picking = self.env['stock.picking'].search([('purchase_id', '=', purchase_order.id)], order='id desc', limit=1)
         self.check_reconciliation(invoice2, picking)
+
+    def test_rounding_discount(self):
+        self.env.ref("product.decimal_discount").digits = 5
+        tax_exclude_id = self.env["account.tax"].create(
+            {
+                "name": "Exclude tax",
+                "amount": "0.00",
+                "type_tax_use": "purchase",
+            }
+        )
+
+        test_product = self.test_product_delivery
+        test_product.supplier_taxes_id = [(6, 0, tax_exclude_id.ids)]
+        date_po_and_delivery = '2018-01-01'
+
+        purchase_order = self._create_purchase(test_product, date_po_and_delivery, quantity=10000, set_tax=True)
+        self._process_pickings(purchase_order.picking_ids, date=date_po_and_delivery)
+
+        invoice = self._create_invoice_for_po(purchase_order, '2018-01-01')
+
+        # Set a discount
+        move_form = Form(invoice)
+        with move_form.invoice_line_ids.edit(0) as line_form:
+            line_form.discount = 0.92431
+        move_form.save()
+
+        invoice.action_post()
+
+        # Check the price difference amount.
+        price_diff_line = invoice.line_ids.filtered(lambda l: l.account_id == self.stock_account_product_categ.property_account_creditor_price_difference_categ)
+        self.assertTrue(len(price_diff_line) == 1, "A price difference line should be created")
+        self.assertAlmostEqual(price_diff_line.price_total, -6100.446)
+
+        picking = self.env['stock.picking'].search([('purchase_id','=',purchase_order.id)])
+        self.check_reconciliation(invoice, picking)