**Impacted versions:**
11.0 
**Steps to reproduce:**
  - Create payslip
  - Add a contract with any structure
  - Add a structure in payslip, different from the one defined in step 2
  - Confirm or compute sheet

**Current behavior:**
Payslip is computed using the contract structure

**Expected behavior:**
Payslip should be computed using the payslip structure

**FYI:**  This is an issue because, sometimes, it's necessary to pay the employee using a structure different from their contract, e.g. in case of Christmas bonuses

**Video/Screenshot link (optional):**
[Video](https://www.youtube.com/watch?v=32H01n503uU&feature=youtu.be)


addons/hr_payroll/models/hr_payslip.py
_name = 'hr.payslip.worked_days'
    _description = 'Payslip Worked Days'
    _order = 'payslip_id, sequence'
    name = fields.Char(string='Description', required=True)
    payslip_id = fields.Many2one('hr.payslip', string='Pay Slip', required=True, ondelete='cascade', index=True)
    sequence = fields.Integer(required=True, index=True, default=10)
    code = fields.Char(required=True, help="The code that can be used in the salary rules")
    number_of_days = fields.Float(string='Number of Days')
    number_of_hours = fields.Float(string='Number of Hours')
    contract_id = fields.Many2one('hr.contract', string='Contract', required=True,
        help="The contract for which applied this input")
class HrPayslipInput(models.Model):
    _name = 'hr.payslip.input'
    _description = 'Payslip Input'
    _order = 'payslip_id, sequence'
    name = fields.Char(string='Description', required=True)
    payslip_id = fields.Many2one('hr.payslip', string='Pay Slip', required=True, ondelete='cascade', index=True)
    sequence = fields.Integer(required=True, index=True, default=10)
    code = fields.Char(required=True, help="The code that can be used in the salary rules")
    amount = fields.Float(help="It is used in computation. For e.g. A rule for sales having "
                               "1% commission of basic salary for per product can defined in expression "
                               "like result = inputs.SALEURO.amount * contract.wage*0.01.")
    contract_id = fields.Many2one('hr.contract', string='Contract', required=True,
        help="The contract for which applied this input")
class HrPayslipRun(models.Model):