sync readonly between pricelist and currency

[lepistone]

Addresses #80, see also odoo/odoo#4598.

If we have some states in which the pricelist can be changed but the
currency is readonly, the currency seems to be changed, but while saving
it goes back.

The core purchase module probably needs a similar fix.

[coveralls]

Coverage increased (+0.09%) to 70.23% when pulling 10a7c75 on lepistone:fix-pricelist-to-currency into 6350b06 on OCA:8.0.

[jgrandguillaume]

LGTM, I've tested it. Thanks 👍

[yvaucher]

@lepistone What happens if readonly is not on field in py file but on view in xml file?
It could be great if we could keep it readonly as only the pricelist should be editable.

If it's not possible, I think it would be preferable to link the bug report in the comment (in code).

Otherwise as it fixes the issue #80 👍

[lepistone]

I agree with you @yvaucher, it's probably a bad idea to be able to change the currency to something different from the pricelist currency. Changing that is non-trivial, and changes the design somewhat, so I'm not doing this here. Instead, I added a longer commentary with reference to odoo/odoo#4598 as you suggest.

[yvaucher]

@lepistone Thanks

[lepistone]

as far as making the currency always readonly, I think it makes sense only if the user belongs to both groups group_multi_currency and group_purchase_pricelist: if the user belongs only to the first one, editing the currency directly makes sense.

For that reason I am making this change to currency always readonly in specific code only.