[FIX] account: update balance when changing amount in currency

Before it wasn't done for simplicity, but turns out it is actually quite
simple to do.

task-3167055

closes odoo/odoo#112043

X-original-commit: 21cb20a284a98a59bf5885ad56d231ae337105e1
Signed-off-by: Quentin De Paoli <qdp@odoo.com>
Signed-off-by: William André (wan) <wan@odoo.com>

addons/account/models/account_move.py

@@ -1507,6 +1507,11 @@ class AccountMove(models.Model):
     # ONCHANGE METHODS
     # -------------------------------------------------------------------------
 
+    @api.onchange('date')
+    def _onchange_date(self):
+        if not self.is_invoice(True):
+            self.line_ids._inverse_amount_currency()
+
     @api.onchange('invoice_vendor_bill_id')
     def _onchange_invoice_vendor_bill(self):
         if self.invoice_vendor_bill_id:

addons/account/models/account_move_line.py

@@ -1110,6 +1110,12 @@ class AccountMoveLine(models.Model):
         for line in self:
             if line.currency_id == line.company_id.currency_id and line.balance != line.amount_currency:
                 line.balance = line.amount_currency
+            elif (
+                line.currency_id != line.company_id.currency_id
+                and not line.move_id.is_invoice(True)
+                and not self.env.is_protected(self._fields['balance'], line)
+            ):
+                line.balance = line.company_id.currency_id.round(line.amount_currency / line.currency_rate)
 
     @api.onchange('debit')
     def _inverse_debit(self):

addons/account/tests/test_account_move_entry.py

@@ -441,20 +441,41 @@ class TestAccountMove(AccountTestInvoicingCommon):
             [
                 {
                     'currency_id': self.currency_data['currency'].id,
-                    'amount_currency': 1200.0,
+                    'amount_currency': -1200.0,
                     'debit': 0.0,
-                    'credit': 0.0,
+                    'credit': 400.0,
                 },
                 {
                     'currency_id': self.currency_data['currency'].id,
-                    'amount_currency': -1200.0,
-                    'debit': 0.0,
+                    'amount_currency': 1200.0,
+                    'debit': 400.0,
                     'credit': 0.0,
                 },
             ],
         )
 
-        # Balance and amount currency are totally independant in journal entries if the line has a foreign currency
+        # Change the date to change the currency conversion's rate
+        with Form(move) as move_form:
+            move_form.date = fields.Date.from_string('2017-01-01')
+
+        self.assertRecordValues(
+            move.line_ids.sorted('debit'),
+            [
+                {
+                    'currency_id': self.currency_data['currency'].id,
+                    'amount_currency': -1200.0,
+                    'debit': 0.0,
+                    'credit': 600.0,
+                },
+                {
+                    'currency_id': self.currency_data['currency'].id,
+                    'amount_currency': 1200.0,
+                    'debit': 600.0,
+                    'credit': 0.0,
+                },
+            ],
+        )
+        # You can change the balance manually without changing the currency amount
         with Form(move) as move_form:
             with move_form.line_ids.edit(0) as line_form:
                 line_form.debit = 200