no need for transition_url (theoretically)

{% assign date = include.need_transition_date %}

{% unless site.transition_url %}

<div class="alert alert-danger">

  you need to specify the variable <code>transition_url</code>

  in <code>_config.yml</code>.

</div>

{% endunless %}

{% if date == "true" %}

{% unless site.transition_date_prebeta %}

<div class="alert alert-danger">

{% comment %}

Below we cover the 3 phases of lesson transition towards the Carpentries Workbench:

- transition-step-1 (`transition_url` variable needed): we indicate that there

is a new version of the lesson that is available for testing, and that it will be deprecated in the future.

- transition-step-2 (`transition_url` and `transition_date` variables needed): we indicate that a new version of the lesson is avaiable with a deprecation date.

- transition-step-3 (`transition_url` variable needed): the lesson is fully deprecated, and a redirect is set up to the new URL

Below we cover the 2 phases of lesson transition towards the Carpentries Workbench:

Variables needed:

  - transition_date_prebeta: the date of the prebeta stage

  - transition_date_beta: the date of the beta stage

  - transition_date_prerelease: the date of the prerelease stage

- transition-step-1: We notify that there is a snapshot of the lesson available for testing, and that it will supersede this version.

- transition-step-2 We indicate that this version of the lesson is a snapshot and a new version of the lesson is avaiable and will supersede this version at a given date.

{% endcomment %}

{% elsif site.life_cycle == "transition-step-1" %}

<div class="alert alert-warning life-cycle">

  A snapshot of this lesson from {{ site.transition_date_prebeta }} is being tested on

  <a href='https://carpentries.github.io/workbench'>The Carpentries Workbench</a>: <a href="{{ site.transition_url }}">{{ site.transition_url }}</a>.

  <a href='https://carpentries.github.io/workbench'>The Carpentries Workbench</a>:

  <a href="https://preview.carpentries.org/{{ repo_name }}">https://preview.carpentries.org/{{ repo_name }}</a>.

  <br>

  <b>The Workbench version of this lesson will become default on {{ site.transition_date_prerelease }}</b>.

  <button type="button" style="border: true; position: absolute; top: 10px; right: 27px; color: #383838;" class="close" data-dismiss="alert" aria-label="Close">

<div class="alert alert-danger alert-dismissible life-cycle" role="alert">

  This lesson is a <b>snapshot from {{ site.transition_date_beta }}</b>.

  A newer version is being tested on <a href='https://carpentries.github.io/workbench'>The Carpentries Workbench</a>:

  <a href="{{ site.transition_url }}">{{ site.transition_url }}</a>.

  <a href="https://preview.carpentries.org/{{ repo_name }}">https://preview.carpentries.org/{{ repo_name }}</a>.

  <br>

  <b>The Workbench version of this lesson will become default on {{ site.transition_date_prerelease }}</b>.

  <button type="button" style="border: true; position: absolute; top: 10px; right: 27px; color: #383838;" class="close" data-dismiss="alert" aria-label="Close">