[FIX] hr_holidays: Fix undeterministic crashing tests

The tests in hr_holidays/tests/test_company_leave.py seem like they randomly fail if the default value for
date_to is computed on a different second than the date_from (it's a dict of fields so not ordered).

Cfr https://runbot.odoo.com/runbot/build/3727451 2020-07-30 08:28:32 vs 2020-07-30 08:28:31
for which date_from > date_to.

I imagine the call to leave._onchange_request_parameters() is meant to fix it, but it occurs after
the create() which is flushed immediately, so it's too late and the date_from/date_to SQL constraint
still triggers.

It could happen for real production usage too, so we might want to do something about that outside of tests.
Options include:

1/ making the date_from/date_to fields writeable computed fields, with the compute method setting
   better defaults on both fields at once
2/ alternatively, remove the default=fields.Datetime.now and override default_get instead for
   deterministic defaults on both fields at once

The second solution seemed to be the better one.

closes odoo/odoo#55880

Taskid: 2312029
X-original-commit: 6908ea471dd18182f83c81046f0000a00898fb66
Signed-off-by: Yannick Tivisse (yti) <yti@odoo.com>

addons/hr_holidays/models/hr_leave.py

@@ -82,6 +82,12 @@ class HolidaysRequest(models.Model):
         if 'state' in fields_list and not defaults.get('state'):
             lt = self.env['hr.leave.type'].browse(defaults.get('holiday_status_id'))
             defaults['state'] = 'confirm' if lt and lt.leave_validation_type != 'no_validation' else 'draft'
+
+        now = fields.Datetime.now()
+        defaults.update({
+            'date_from': now,
+            'date_to': now,
+        })
         return defaults
 
     def _default_get_request_parameters(self, values):
@@ -143,11 +149,9 @@ class HolidaysRequest(models.Model):
     # duration
     date_from = fields.Datetime(
         'Start Date', compute='_compute_date_from_to', store=True, readonly=False, index=True, copy=False, required=True, tracking=True,
-        default=fields.Datetime.now,
         states={'cancel': [('readonly', True)], 'refuse': [('readonly', True)], 'validate1': [('readonly', True)], 'validate': [('readonly', True)]})
     date_to = fields.Datetime(
         'End Date', compute='_compute_date_from_to', store=True, readonly=False, copy=False, required=True, tracking=True,
-        default=fields.Datetime.now,
         states={'cancel': [('readonly', True)], 'refuse': [('readonly', True)], 'validate1': [('readonly', True)], 'validate': [('readonly', True)]})
     number_of_days = fields.Float(
         'Duration (Days)', compute='_compute_number_of_days', store=True, readonly=False, copy=False, tracking=True,
@@ -309,7 +313,7 @@ class HolidaysRequest(models.Model):
                 'request_unit_half', 'request_unit_hours', 'request_unit_custom', 'employee_id')
     def _compute_date_from_to(self):
         for holiday in self:
-            if holiday.request_date_from > holiday.request_date_to:
+            if holiday.request_date_from and holiday.request_date_to and holiday.request_date_from > holiday.request_date_to:
                 holiday.request_date_to = holiday.request_date_from
             if not holiday.request_date_from:
                 holiday.date_from = False

addons/hr_holidays/tests/test_leave_requests.py

@@ -168,6 +168,8 @@ class TestLeaveRequests(TestHrHolidaysCommon):
         leave_form.holiday_type = 'department'
         leave_form.department_id = self.hr_dept
         leave_form.holiday_status_id = self.holidays_type_1
+        leave_form.request_date_from = date(2019, 5, 6)
+        leave_form.request_date_to = date(2019, 5, 6)
         leave = leave_form.save()
         leave.action_approve()
         member_ids = self.hr_dept.member_ids.ids