[FIX] account: tax line amount

The company currency is USD, the invoice currency is EUR.
- Create an invoice in EUR, set an invoice date
- Compute the taxes (click on "update" button)
- Change the exchange rate between EUR and USD
- Validate the invoice

At validation, the tax lines are not recomputed. Therefore, the tax
amounts, are still converted in the company currency using the old
rates. On the other hands, the other account move lines will have the
appropriate new rate.

Closes #14024
opw-692430

addons/account/account_invoice.py

@@ -20,6 +20,7 @@
 ##############################################################################
 
 import itertools
+import math
 from lxml import etree
 
 from openerp import models, fields, api, _
@@ -741,8 +742,6 @@ class account_invoice(models.Model):
                 line['currency_id'] = currency.id
                 line['amount_currency'] = currency.round(line['price'])
                 line['price'] = currency.compute(line['price'], company_currency)
-                if line.get('tax_amount'):
-                    line['tax_amount'] = currency.compute(line['tax_amount'], company_currency)
             else:
                 line['currency_id'] = False
                 line['amount_currency'] = False
@@ -845,6 +844,9 @@ class account_invoice(models.Model):
                 if (total_fixed + total_percent) > 100:
                     raise except_orm(_('Error!'), _("Cannot create the invoice.\nThe related payment term is probably misconfigured as it gives a computed amount greater than the total invoiced amount. In order to avoid rounding issues, the latest line of your payment term must be of type 'balance'."))
 
+            # Force recomputation of tax_amount, since the rate potentially changed between creation
+            # and validation of the invoice
+            inv._recompute_tax_amount()
             # one move line per tax line
             iml += account_invoice_tax.move_line_get(inv.id)
 
@@ -1227,6 +1229,18 @@ class account_invoice(models.Model):
         return account_invoice.pay_and_reconcile(recs, pay_amount, pay_account_id, period_id, pay_journal_id,
                     writeoff_acc_id, writeoff_period_id, writeoff_journal_id, name=name)
 
+    @api.multi
+    def _recompute_tax_amount(self):
+        for invoice in self:
+            if invoice.currency_id != invoice.company_id.currency_id:
+                for line in invoice.tax_line:
+                    tax_amount = line.amount_change(
+                        line.amount, currency_id=invoice.currency_id.id, company_id=invoice.company_id.id,
+                        date_invoice=invoice.date_invoice
+                    )['value']['tax_amount']
+                    line.write({'tax_amount': tax_amount})
+
+
 class account_invoice_line(models.Model):
     _name = "account.invoice.line"
     _description = "Invoice Line"
@@ -1553,7 +1567,7 @@ class account_invoice_tax(models.Model):
             currency = self.env['res.currency'].browse(currency_id)
             currency = currency.with_context(date=date_invoice or fields.Date.context_today(self))
             amount = currency.compute(amount, company.currency_id, round=False)
-        tax_sign = (self.tax_amount / self.amount) if self.amount else 1
+        tax_sign = math.copysign(1, (self.tax_amount * self.amount))
         return {'value': {'tax_amount': amount * tax_sign}}
 
     @api.v8