[IMP] account : Allow payment of 0 amount in write-off balance

The user can register a payment of 0 amount with "Mark Invoice as Paid" option and selecting an account to post the difference.

task: https://www.odoo.com/web#id=29959&view_type=form&model=project.task&action=333&active_id=131&menu_id=4720
PR: odoo#16429

addons/account/models/account_payment.py

@@ -56,8 +56,8 @@ class account_abstract_payment(models.AbstractModel):
     @api.one
     @api.constrains('amount')
     def _check_amount(self):
-        if not self.amount > 0.0:
-            raise ValidationError(_('The payment amount must be strictly positive.'))
+        if self.amount < 0:
+            raise ValidationError(_('The payment amount cannot be negative.'))
 
     @api.multi
     @api.depends('payment_type', 'journal_id')
@@ -309,6 +309,24 @@ def open_payment_matching_screen(self):
             'context': action_context,
         }
 
+    @api.onchange('amount', 'currency_id')
+    def _onchange_amount(self):
+        journal_type = ['bank', 'cash']
+        domain = []
+        if self.currency_id.is_zero(self.amount):
+            # In case of payment with 0 amount, allow to select a journal of type 'general' like
+            # 'Miscellaneous Operations' and set this journal by default.
+            journal_type.append('general')
+            self.payment_difference_handling = 'reconcile'
+            self.journal_id = self.env['account.journal'].search([('type', '=', 'general')], limit=1)
+        else:
+            if self.payment_type == 'inbound':
+                domain.append(('at_least_one_inbound', '=', True))
+            else:
+                domain.append(('at_least_one_outbound', '=', True))
+        domain.append(('type', 'in', journal_type))
+        return {'domain': {'journal_id': domain}}
+
     @api.one
     @api.depends('invoice_ids', 'payment_type', 'partner_type', 'partner_id')
     def _compute_destination_account_id(self):
@@ -526,18 +544,19 @@ def _create_payment_entry(self, amount):
             writeoff_line['amount_currency'] = amount_currency_wo
             writeoff_line['currency_id'] = currency_id
             writeoff_line = aml_obj.create(writeoff_line)
-            if counterpart_aml['debit']:
+            if counterpart_aml['debit'] or writeoff_line['credit']:
                 counterpart_aml['debit'] += credit_wo - debit_wo
-            if counterpart_aml['credit']:
+            if counterpart_aml['credit'] or writeoff_line['debit']:
                 counterpart_aml['credit'] += debit_wo - credit_wo
             counterpart_aml['amount_currency'] -= amount_currency_wo
 
         #Write counterpart lines
-        if not self.currency_id != self.company_id.currency_id:
-            amount_currency = 0
-        liquidity_aml_dict = self._get_shared_move_line_vals(credit, debit, -amount_currency, move.id, False)
-        liquidity_aml_dict.update(self._get_liquidity_move_line_vals(-amount))
-        aml_obj.create(liquidity_aml_dict)
+        if not self.currency_id.is_zero(self.amount):
+            if not self.currency_id != self.company_id.currency_id:
+                amount_currency = 0
+            liquidity_aml_dict = self._get_shared_move_line_vals(credit, debit, -amount_currency, move.id, False)
+            liquidity_aml_dict.update(self._get_liquidity_move_line_vals(-amount))
+            aml_obj.create(liquidity_aml_dict)
 
         #validate the payment
         move.post()

addons/account/views/account_payment_view.xml

@@ -230,15 +230,15 @@
                             <field name="partner_id" invisible="1"/>
                             <field name="state" invisible="1"/>
                             <group>
-                                <field name="journal_id" widget="selection"/>
-                                <field name="hide_payment_method" invisible="1"/>
-                                <field name="payment_method_id" widget="radio" attrs="{'invisible': [('hide_payment_method', '=', True)]}"/>
-                                <field name="payment_method_code" invisible="1"/>
                                 <label for="amount"/>
                                 <div name="amount_div" class="o_row">
                                     <field name="amount"/>
                                     <field name="currency_id" options="{'no_create': True, 'no_open': True}" groups="base.group_multi_currency"/>
                                 </div>
+                                <field name="journal_id" widget="selection" attrs="{'invisible': [('amount', '=', 0)]}"/>
+                                <field name="hide_payment_method" invisible="1"/>
+                                <field name="payment_method_id" widget="radio" attrs="{'invisible': ['|', ('hide_payment_method', '=', True), ('amount', '=', 0.0)]}"/>
+                                <field name="payment_method_code" invisible="1"/>
                             </group>
                             <group>
                                 <field name="payment_date"/>
@@ -252,6 +252,8 @@
                                     <div attrs="{'invisible': [('payment_difference_handling','=','open')]}">
                                         <label for="writeoff_account_id" class="oe_edit_only" string="Post Difference In"/>
                                         <field name="writeoff_account_id" string="Post Difference In" attrs="{'required': [('payment_difference_handling', '=', 'reconcile')]}"/>
+                                        <label string="Journal" attrs="{'invisible': [('amount', '!=', 0)]}"/>
+                                        <field name="journal_id" string="Journal" widget="selection" attrs="{'invisible': [('amount', '!=', 0)]}"/>
                                         <label for="writeoff_label" class="oe_edit_only" string="Label"/>
                                         <field name="writeoff_label" attrs="{'required': [('payment_difference_handling', '=', 'reconcile')]}"/>
                                     </div>

addons/account_check_printing/models/account_payment.py

@@ -68,9 +68,9 @@ def _onchange_journal_id(self):
 
     @api.onchange('amount')
     def _onchange_amount(self):
-        if hasattr(super(AccountPayment, self), '_onchange_amount'):
-            super(AccountPayment, self)._onchange_amount()
+        res = super(AccountPayment, self)._onchange_amount()
         self.check_amount_in_words = self._get_check_amount_in_words(self.amount)
+        return res
 
     def _check_communication(self, payment_method_id, communication):
         super(AccountPayment, self)._check_communication(payment_method_id, communication)