Support categories/tags on posts

[johannhof]

Would be nice to be able to define a number of categories in front matter that would then be available as e.g. a Liquid object for rendering.

[uwearzt]

I started to work on this.

[ducks]

Howdy @uwearzt. I was curious if you had made any progress on this. I was thinking of poking at it a bit but don't want to step on your toes if you're close to a PR or anything.

[uwearzt]

Hi, I am making slow progress ;), too much work to do. I will push the intermediate progress on Monday or Tuesday. Then we can work together...

[uwearzt]

See #196 for a first take. I am especially interested in reviewing the categories.liquid file and if it is OK to add preserve_order to rust-yaml.

[epage]

@uwearzt, could you describe how you imagine categories working?

[uwearzt]

@epage

1. Add Categories to your posts (the categories are also used for jsonfeed)

categories: [CatE, SubCatC]

2. Add Categories to the cobalt.yml file

categories: [ CatA : [],
              CatB : [ SubCatC, SubCatD ],
              CatE : [ SubCatF ]]

there will be (at least) a info message if you use a category inside a post which is not defined here.

3. Use them for a Tree with posts:

<div>
  <h3>print categories with posts</h3>
    <!-- check if there are categories in config -->
    {%if site.categories %}
      <!-- run over categories -->
      {% for category in site.categories %}
        <h4>{{ category.name }}</h4>
        <!-- run over posts -->
        {% if category.posts %}
          Posts in this category<br/>
          {% for post in category.posts %}
            {{ post.date | date: "%d.%m.%Y" }} | {{ post.title }}<br/>
          {% endfor %}
        {% endif %}
        <!-- run over subcategories -->
        {% if category.subcategories %}
          {% for subcategory in category.subcategories %}
            <h5>{{ subcategory.name }}</h5>
            <!-- run over posts -->
            {% if subcategory.posts %}
              Posts in this subcategory<br/>
              {% for post in subcategory.posts %}
                {{ post.date | date: "%d.%m.%Y" }} | {{ post.title }}<br/>
              {% endfor %}
            {% endif %}
          {% endfor %}
        {% endif %}
      {% endfor %}
    {% endif %}
</div>

[epage]

So defining categories in cobalt.yml is meant to

1. Perform validity checking on frontmatter categories
2. Simplify creation of category attributes for or use in some kind of index page

One of my concerns is creating the tree of posts for all pages, causing lots of memory bloat / copies. I have an idea for improving this in liquid (supporting overlaying liquid::Objects

I'm also interested in learning more about hugo's _index.md.

btw my PR I'm preparing will allow using :categories in the frontmatter path.

[epage]

#257 has added support for :categories when generating an output path.

[epage]

#354 is tracking work on doing something like Hugo's _index.md

[epage]

I think between our pagination work and the other issues, this is resolved.