[FIX] account: unbalanced entry with price_unit 0

Steps to reproduce:

- Create invoice for a prudict at price X > 0
- Change the price to 0 before saving
- Then save it
-> Error : Cannot create unbalanced journal entry

This bug was introduced in 14.0 with this commit fe7d56dc32c71e04b54de9dbd756a48942a832f4
With this commit, we use an ugly condition to catch the
specific case of a tax with price included and amount type division
to avoid changing the price unit if the line balance is zero.

opw-2822635

closes odoo/odoo#91059

X-original-commit: 2b9592cb0ecef235d708ed7810d0613ccd946124
Signed-off-by: Laurent Smet <las@odoo.com>
Signed-off-by: Guillaume Vanleynseele <guva@odoo.com>

addons/account/models/account_move.py

@@ -3897,6 +3897,7 @@ class AccountMoveLine(models.Model):
                 if tax.price_include:
                     amount_currency += tax_res['amount']
 
+        tax_included_division_is_zero = any(tax.price_include and tax.amount == 100 and tax.amount_type == 'division' for tax in taxes) and amount_currency == 0
         discount_factor = 1 - (discount / 100.0)
         if amount_currency and discount_factor:
             # discount != 100%
@@ -3911,8 +3912,9 @@ class AccountMoveLine(models.Model):
                 'discount': 0.0,
                 'price_unit': amount_currency / (quantity or 1.0),
             }
-        elif not discount_factor:
-            # balance of line is 0, but discount  == 100% so we display the normal unit_price
+        elif not discount_factor or tax_included_division_is_zero:
+            # balance of line is 0, but discount == 100% or taxes (price included) == 100%,
+            # so we display the normal unit_price
             vals = {}
         else:
             # balance is 0, so unit price is 0 as well

addons/account/tests/test_account_move_out_invoice.py

@@ -3449,3 +3449,24 @@ class TestAccountMoveOutInvoiceOnchanges(AccountTestInvoicingCommon):
 
         # Tags should be empty since the tax has been removed from the invoice line
         self.assertRecordValues(invoice.line_ids, [{'tax_tag_ids': []}, {'tax_tag_ids': []}])
+
+    def test_changeprice_unit_to_zero(self):
+        move = self.env['account.move'].create({
+            'move_type': 'out_invoice',
+            'partner_id': self.partner_a.id,
+            'invoice_date': fields.Date.from_string('2017-01-01'),
+            'invoice_line_ids': [
+                (0, None, {
+                    'product_id': self.product_a.id,
+                    'product_uom_id': self.product_a.uom_id.id,
+                    'quantity': 1.0,
+                    'price_unit': 1000.0,
+                    'tax_ids': [(6, 0, [])],
+                })]
+        })
+
+        move.write({'invoice_line_ids': [(1, move.invoice_line_ids.ids[0], {
+            'price_unit': 0.0,
+        })]})
+
+        self.assertTrue(all(line.price_unit == 0 for line in move.line_ids))

addons/account/tests/test_invoice_taxes.py

@@ -713,3 +713,41 @@ class TestInvoiceTaxes(AccountTestInvoicingCommon):
         self.assertRecordValues(invoice.line_ids.filtered(lambda l: l.account_id.internal_type == 'receivable'), [{
             'balance': 686.54
         }])
+
+    def test_invoice_with_100_percent_division_tax_incl(self):
+        """
+        Check if the price unit remain the same after affecting a tax
+        100%, price_include and amount_type 'division'
+        """
+        invoice = self.env['account.move'].create({
+            'move_type': 'out_invoice',
+            'partner_id': self.partner_a.id,
+            'currency_id': self.currency_data['currency'].id,
+            'invoice_date': '2018-01-01',
+            'date': '2018-01-01',
+            'invoice_line_ids': [(0, 0, {
+                'name': 'xxxx',
+                'quantity': 1,
+                'price_unit': 500,
+            })]
+        })
+
+        division_tax_4_incl = self.env['account.tax'].create({
+            'name': '100% incl',
+            'amount_type': 'division',
+            'amount': 100,
+            'price_include': True,
+            'include_base_amount': True,
+            'sequence': 50,
+        })
+
+        self.assertRecordValues(invoice.invoice_line_ids, [
+            {'price_unit': 500}
+        ])
+        with Form(invoice) as inv_form:
+            with inv_form.invoice_line_ids.edit(0) as line_form:
+                line_form.tax_ids.add(division_tax_4_incl)
+
+        self.assertRecordValues(invoice.invoice_line_ids, [
+            {'price_unit': 500}
+        ])