Manual amount in manual invoice taxes

I don’t know if it was done on purpose or not.

Invoice taxes (lower-left corner of the invoice form) can be computed automatically from the content of invoice lines and the user can change the computed amount without problems.

It is also possible to create new tax lines manually. In this case, if the user selects a tax, it is possible to define the base of the tax but it is not possible to change the amount. If amount is changed by the user, Tryton automatically puts the computed tax again.

This is due to this on_change_with method:

Is this on purpose?

We’ve got some cases in which it would be useful to add manual taxes but we need to be able to change the amount manually too.

A tax with None type will not trigger any computation.

Yes, but it also does not allow to have a default account because the fields are hidden in the tax definition.

Well, it would be a good improvement to have a method that allows to re-compute the amount when the base is changed but not when the amount is modified (like it is done for non-manual taxes).

I added Issue 8618: Allow changing amount in manual invoice taxes - Tryton issue tracker