From ebac669b2e1f2b71ce8b3ad9b277193c5e0db69f Mon Sep 17 00:00:00 2001
From: Nicolas Martinelli <nim@odoo.com>
Date: Thu, 6 Aug 2020 13:35:15 +0000
Subject: [PATCH] [FIX] account: tax rounding error

- Create Tax 0:
  Percentage
  Amount: 0
  Tax Included
  Tax Group 0
- Create Tax 8:
  Percentage
  Amount: 8
  Tax Included
  Tax Group 8
- Create a customer invoice with one line
  Quantity: 8.0
  Price Unit: 15.55
  Taxes: Tax 8, Tax 0 (order is important)

The tax amounts are:
  Tax 8: 9.22
  Tax 0: -0.01

If the taxes are inverted, the tax amounts
  Tax 8: 9.21
  Tax 0: 0.00

The difference is due to the rounding of the 8% tax done differently. In
the second case, the computation of the 8% tax goes through:

https://github.com/odoo/odoo/blob/8c5cd335a57c20ed5faa6b7c7630c296c1f2a5cf/addons/account/models/account.py#L1480

In the first case, the amount is recomputed in:

https://github.com/odoo/odoo/blob/8c5cd335a57c20ed5faa6b7c7630c296c1f2a5cf/addons/account/models/account.py#L1483

The rounding is different in both cases, leading to an inconsistency.

When the tax amount is zero, there is no need to save the amount in
`total_included_checkpoints`.

opw-2306676

closes odoo/odoo#55812

X-original-commit: e2776e188070221ef465a864bd2cb8dcfc971e14
Signed-off-by: Jorge Pinna Puissant (jpp) <jpp@odoo.com>
---
 addons/account/models/account_tax.py |  7 +++-
 addons/account/tests/test_tax.py     | 50 ++++++++++++++++++++++++++++
 2 files changed, 56 insertions(+), 1 deletion(-)

diff --git a/addons/account/models/account_tax.py b/addons/account/models/account_tax.py
index 19977d46831..d599d06f788 100644
--- a/addons/account/models/account_tax.py
+++ b/addons/account/models/account_tax.py
@@ -492,7 +492,12 @@ class AccountTax(models.Model):
                         incl_fixed_amount += tax_amount
                         # Avoid unecessary re-computation
                         cached_tax_amounts[i] = tax_amount
-                    if store_included_tax_total:
+                    # In case of a zero tax, do not store the base amount since the tax amount will
+                    # be zero anyway. Group and Python taxes have an amount of zero, so do not take
+                    # them into account.
+                    if store_included_tax_total and (
+                        tax.amount or tax.amount_type not in ("percent", "division", "fixed")
+                    ):
                         total_included_checkpoints[i] = base
                         store_included_tax_total = False
                 i -= 1
diff --git a/addons/account/tests/test_tax.py b/addons/account/tests/test_tax.py
index a038f9c272a..1964d626c96 100644
--- a/addons/account/tests/test_tax.py
+++ b/addons/account/tests/test_tax.py
@@ -124,6 +124,17 @@ class TestTaxCommon(AccountTestInvoicingCommon):
             ],
         })
 
+        cls.tax_0_percent = cls.env['account.tax'].with_company(cls.company_data['company']).create({
+            'name': "test_0_percent",
+            'amount_type': 'percent',
+            'amount': 0,
+        })
+
+        cls.tax_8_percent = cls.env['account.tax'].with_company(cls.company_data['company']).create({
+            'name': "test_8_percent",
+            'amount_type': 'percent',
+            'amount': 8,
+        })
         cls.tax_12_percent = cls.env['account.tax'].with_company(cls.company_data['company']).create({
             'name': "test_12_percent",
             'amount_type': 'percent',
@@ -828,6 +839,45 @@ class TestTax(TestTaxCommon):
             res1
         )
 
+    def test_rounding_tax_included_round_per_line_03(self):
+        ''' Test the rounding of a 8% and 0% price included tax in an invoice having 8 * 15.55 as line.
+        The decimal precision is set to 2.
+        '''
+        self.tax_0_percent.company_id.currency_id.rounding = 0.01
+        self.tax_0_percent.price_include = True
+        self.tax_8_percent.price_include = True
+
+        self.group_tax.children_tax_ids = [(6, 0, self.tax_0_percent.ids)]
+        self.group_tax_bis.children_tax_ids = [(6, 0, self.tax_8_percent.ids)]
+
+        res1 = (self.tax_8_percent | self.tax_0_percent).compute_all(15.55, quantity=8.0)
+        self._check_compute_all_results(
+            124.40,      # 'total_included'
+            115.19,      # 'total_excluded'
+            [
+                # base , amount
+                # -------------
+                (115.19, 9.21),
+                (115.19, 0.00),
+                # -------------
+            ],
+            res1
+        )
+
+        res2 = (self.tax_0_percent | self.tax_8_percent).compute_all(15.55, quantity=8.0)
+        self._check_compute_all_results(
+            124.40,      # 'total_included'
+            115.19,      # 'total_excluded'
+            [
+                # base , amount
+                # -------------
+                (115.19, 0.00),
+                (115.19, 9.21),
+                # -------------
+            ],
+            res2
+        )
+
     def test_rounding_tax_included_round_globally_01(self):
         ''' Test the rounding of a 19% price included tax in an invoice having 27000 and 10920 as lines.
         The decimal precision is set to zero.