.. _tutorial_propertyerror:

The Jinja propertyerror test
============================

.. objectives:: Objectives

   In a :ref:`Jinja-type calculation <tutorial_jinja>`, it is possible to test if a variable is accessible (there is no :ref:`access_control` problem).

.. prerequisites:: Prerequisites

    - We assume that Rougail's library is :ref:`installed <installation>` on your computer.

    - It is possible to retrieve the current state of the various Rougail files manipulated in this tutorial step
      by checking out the corresponding tag of the `rougail-tutorials` git repository.
      Each tag corresponds to a stage of progress in the tutorial.
      Of course, you can also decide to copy/paste or download the tutorial files contents while following the tutorial steps.

    If you want to follow this tutorial with the help of the corresponding :tutorial:`rougail-tutorials git repository <src/branch/1.1>`, 
    this workshop page corresponds to the tag :tutorial:`v1.1_140 <src/tag/v1.1_140/README.md>` in the repository:

    ::
   
       git clone https://forge.cloud.silique.fr/stove/rougail-tutorials.git
       git switch --detach v1.1_140

For now, the variable `proxy_dns_socks5` defines these access controls as follows:

- if the `proxy_mode` variable is not set to `"Manual proxy configuration"`
- if socks version is `v4`.

.. extinclude:: https://forge.cloud.silique.fr/stove/rougail-tutorials/raw/commit/v1.1_131/firefox/55-proxy_dns_socks5.yml
   :language: yaml 
   :caption: The :file:`firefox/55-proxy_dns_socks5.yml`

In principle it works, but is that really what we want? We mean, do we want to disable it based on the proxy_mode variable?

No, we actually want to make this variable available if the socks version is accessible and equals v4.

Disabled a variable when an other variable is disabled
-------------------------------------------------------

The most suitable syntax in Jinja for checking the status of a variable is to use the `concept of a test <https://jinja.palletsprojects.com/en/stable/templates/#tests>`_.

Rougail offers a custom test that will verify correct access to the variable.

This test is call `propertyerror`.

Here is how one could write the Jinja using this feature:

.. extinclude:: https://forge.cloud.silique.fr/stove/rougail-tutorials/raw/commit/v1.1_140/firefox/55-proxy_dns_socks5.yml
   :language: yaml 
   :caption: The :file:`firefox/55-proxy_dns_socks5.yml` structure file with some Jinja code in the `hidden` property

.. keypoints:: Key points

   We have seen that we can use the test `propertyerror` in Jinja template.
