Add separator to For tag

[nickpearson]

This adds the ability to add a separator to be outputted between iterations of a for loop.

For example, to add commas between elements:

{% for item in items separator: ', ' %}{{ item }}{% endfor %}

Without this, you have to use a conditional to avoid outputting a separator after the last element:

{% for item in items %}{{ item }}{% unless forloop.last %}, {% endunless %}{% endfor %}

For such a trivial case shown above, the join filter could be used. However, the separator option is useful when there's more than just a simple output inside the loop:

{% for item in items separator: '<br>' %}
  <b>{{ item.title | upcase }}</b>
{% endfor %}

Benchmarks on master:

[lax]
              parse:     24.582  (± 0.0%) i/s -      1.476k
        parse & run:     16.395  (± 0.0%) i/s -    984.000

[strict]
              parse:     20.304  (± 0.0%) i/s -      1.218k
        parse & run:     14.303  (± 0.0%) i/s -    858.000

Benchmark with the new separator:

[lax]
              parse:     25.058  (± 0.0%) i/s -      1.504k
        parse & run:     16.546  (± 0.0%) i/s -    993.000

[strict]
              parse:     20.175  (± 0.0%) i/s -      1.210k
        parse & run:     14.285  (± 0.0%) i/s -    857.000

@fw42 please review when you get a chance.

[fw42]

Isn't this the same as {{ items | join: ", " }}?

[fw42]

Sorry, I should read the whole description before answering :-)

[fw42]

I'm pretty indifferent about this... @pushrax @dylanahsmith?

@carolineschnapp you think this would be useful?

[carolineschnapp]

It could be useful yes :+1:

A did a Find in Files for {% unless forloop.last %} in our own themes and it's always the same scenarios that will be helped by this.

1. A comma separated list of tags that are links:

{% for tag in article.tags %}
 <a href="{{ blog.url }}/tagged/{{ tag | handle }}">{{ tag }}</a>{% unless forloop.last %}, {% endunless %}
{% endfor %}

2. Listing articles, comments, or search results, with a divider line between them (CSS could be used instead but it isn't):

   {% unless forloop.last %}
   <hr class="divider" />
   {% endunless %}
   

3. Separator between links in link list:

   {% for link in linklists.footer.links %}<a href="{{ link.url }}">{{ link.title | escape }}</a>{% unless forloop.last %} <span>&#124;</span>
   

[pushrax]

Indifferent as well, I don't mind this but I also think many cases should be accomplished with lists and CSS instead.

[pushrax]

Code looks good in either case.

[nickpearson]

Thanks @pushrax. For what it's worth, I've been using this in production for a few years now, and it comes in handy pretty often and reduces the noise in otherwise trivial for loops.

[fw42]

@nickpearson: Can you rebase this?

[nickpearson]

@fw42 Sure thing — all done.

[rickydazla]

:+1: