[FIX] point_of_sale: modify tax

Prevent the modification of a tax which is used in an opened POS
session. This avoids inconsistency between the payment and the order
accounting entries.

opw-1859092

addons/point_of_sale/i18n/point_of_sale.pot

@@ -1584,6 +1584,11 @@ msgstr ""
 msgid "It acts as a default account for debit amount"
 msgstr ""
 
+#: code:addons/point_of_sale/models/account_tax.py:18
+#, python-format
+msgid "It is forbidden to modify a tax used in a POS order not posted. You must close the POS sessions before modifying the tax."
+msgstr ""
+
 #. module: point_of_sale
 #: model:ir.model,name:point_of_sale.model_account_journal
 #: model:ir.model.fields,field_description:point_of_sale.field_report_pos_order__journal_id

addons/point_of_sale/models/__init__.py

@@ -3,6 +3,7 @@
 
 from . import account_bank_statement
 from . import account_journal
+from . import account_tax
 from . import barcode_rule
 from . import pos_category
 from . import pos_config

addons/point_of_sale/models/account_tax.py

+# -*- coding: utf-8 -*-
+
+from odoo import _, api, models
+from odoo.exceptions import UserError
+
+
+class AccountTax(models.Model):
+    _inherit = 'account.tax'
+
+    @api.multi
+    def write(self, vals):
+        forbidden_fields = set([
+            'amount_type', 'amount', 'type_tax_use', 'tax_group_id', 'price_include',
+            'include_base_amount'
+        ])
+        if forbidden_fields & set(vals.keys()):
+            tax_ids = self.env['pos.order.line'].sudo().search([
+                ('order_id.session_id.state', '!=', 'closed')
+            ]).read(['tax_ids'])
+            # Flatten the list of taxes, see https://stackoverflow.com/questions/952914
+            tax_ids = set([i for sl in [t['tax_ids'] for t in tax_ids] for i in sl])
+            if tax_ids & set(self.ids):
+                raise UserError(_(
+                    'It is forbidden to modify a tax used in a POS order not posted. ' +
+                    'You must close the POS sessions before modifying the tax.'
+                ))
+        return super(AccountTax, self).write(vals)