Thanks a lot for these explanations. I think I start to be agree with you.


> Why not using the hierarchy in the rules for this ?

> Have a look at the meal voucher rule in the l10n_be_hr_payroll, this may solve your issue. For a
> meal voucher of 6.00 EUR in Belgium, there is 1.09 paid by the employee (deduced from it's gross 
> salary) and 4.81 paid by the company (to Accor for example). To manage this we do:
>  - one rule (Meal Voucher)
>       - Children 1: company contribution
>       - Children 2: employee contribution


I suppose this happen but I feel a bit ashamed here... How I could missed that, you're totally right the rules hierarchy could totally handle the link. I still don't know if it'll be ergonomic enough for the users who will modify the employer contributions in the payslip but at least it worth a try.



> If the report requires to print both rule in one line, I think it's better to implement this at 
> the report level, rather than changing.

> Sorry if I look strict on this, but IMHO if something can be computed by the current payroll 
> engine, it's better not to develop specific rules for specific cases. Payrolls are so complex 
> that we could potentially add lots of fields and logic if we don't rely on a strong computation 
> engine.

Don't worry, I think this is the good way to do it, no change unless necessary. Even me was careful with the merge here to not make big changes.



> What's the french translation of employer deduction ? (Charges patronales ? sociales?)

The term is "Cotisations Patronales" but "Charges Patronales" is ok too. We have also "Cotisations Salariales" for the employee contribution.
The translation of theses terms is difficult, some research make me think that "employer contribution" and "employee contribution" is a good translation, rather than deduction, but well I'm not a linguist.


> If you create a better, and generic, report I think it's better to merge it directly in the 
> hr_payroll module in replacement to the Payslip Details report. All countries will need it. The 
> example you took from ciel seems to be generic, we just need to identify some salary rule 
> categories code that have a special meaning, like NET.

Good news we are agree on this point. You can account on me to do it, but now I will before begin the l10n_fr_hr_payroll module for having some data test asap.

Just one point : I'm still unsure I'll not have to redefine the report in l10n_fr_hr_payroll because some France specific data appear (Like URSSAF, SIRET, "Plafond de sécurité sociale" etc...)



> The whole structure in the columns of your document seems generic (salaire de base, salaire brut, 
> total retenues, ...). If I am not wrong, the left column Mt. Sal contains all rules having 
> "Appears on Payslip" checked whereas the right column Mt.PAT is all not having 'Appears on 
> payslip" checked. Is some rule belong to the same parent, they should be on the same line.
>     --> this makes me wonder if "Appears on Payslip" is the right label?

Don't worry, I think the "Appears on Payslip is good and don't need to be change. We'll probably need that some lines which are not employer contribution doesn't appear in the payslip.
But a contribution line have just one employer contribution, so we may have a problem if the parent rule have more than one child rule. I think a check-box "Employer contribution?" will be useful for identifying the child line which will be used as employer contribution.


So I begin to write the l10n_fr_hr_payroll module. Once it'll done I'll probably try to merge theses changes in hr_payroll :
       -A checkbox "Employer contribution" in child rules for identifying the employer contribution rule.
       -Some many2one field "Basic" "Gross" "Net" in the configuration somewhere (company configuration?) which lead to Hr Salary Category object. Then I should be able to call the value of theses category on the report without make hard-link in the report itself.
       -Creation of a better payslip report. Although I still think I'll need to redefine it in l10n_fr_hr_payroll.


One again thanks for your advices, I go back to work. Stay tune.