The simplest way I can find to find a sorted list of all tags across all posts in Siteleaf.

tags.html

{% capture tags %}
 	{% for post in site.posts %}
  		{% for tag in post.taxonomy.tags %}
			{{tag.value}}\{{tag.url}}{% unless forloop.last %},{% endunless %}
		{% endfor %}
	{% endfor %}
{% endcapture %}

{% assign tags = tags | strip_newlines | split:',' | sort %}

<ul>
{% for tag in tags %}
	{% assign tag_parts = tag | split:'\' %}

	{% unless last_tag == tag_parts.first %}
		<li><a href="{{tag_parts.last}}">{{tag_parts.first}}</a></li>
	{% endunless %}

	{% assign last_tag = tag_parts.first %}
{% endfor %}
</ul>

1. Iterate over all posts
2. Build a string of tags formatted like tag\url, each separated with a ,
3. Explode the string into an array of tag\url items
4. Sort the array alphabetically
5. Iterate over the array and take note of the previous item so you can skip duplicates

Tags are scoped to the page-level (ie. blog), so you can use the following code to get all tags used on your blog posts (sorted alphabetically):

<ul>
    {% assign sorted_tags = site.pages['blog'].taxonomy['tags'].values | sort:'value' %}
    {% for tag in sorted_tags %}
    <li><a href="{{tag.url}}">{{tag.value}}</a></li>
    {% endfor %}
  </ul>

Swap blog for your page's slug, and tags for the name of your tagset (if not using the default tags).

Very cool, this works perfectly, thanks for the speedy work on this too!

While this is perfect, I have a few questions to better my understanding.

1. In the line site.pages['blog'].taxonomy['tags'].values, what is the values member? It’s not mentioned in siteleaf-themes. Syntactically it’s a bit confusing to me because it looks like we’re not iterating over the tags array itself, but some child of it.
2. Passing a key to sort is awesome. It’s a shame it’s not in the Liquid For Designers docs.
3. I’ve found it’s perhaps impossible to iterate over a filtered array in a for loop. For instance, I often run into trouble with a line like {% for tag in site.pages.blog.taxonomy.tags.values | sort:'value' %}, even when wrapping the in clause in ( ). Is this syntactically invalid or is there some subtlety I’m overlooking?

Also,

💖 💖 💖

1. In Siteleaf you can call your tag set anything you want (default is 'tags', but can be anything). values is the generic name for the array of 'tag' values. Here is what the data looks like behind the scenes:

https://github.com/siteleaf/siteleaf-api#get-v1taxonomyidjson

We'll update the theme docs to make this more clear.

2. Agreed, they list it but don't explain it further.

3. You can't sort on a for statement, but you can sort first and assign it to a new variable like this:

{% assign sorted_tags = site.pages['blog'].taxonomy['tags'].values | sort:'value' %}

Now you can use the sorted_tags variable:

{% for tag in sorted_tags %}
    <li><a href="{{tag.url}}">{{tag.value}}</a></li>
{% endfor %}