Don't delete category and tag properties when merging them into categories and tags, respectively

[tyxchen]

In one of my projects, we found that if a page parsed by jekyll-asciidoc inside a collection has a category added to it, that category will not be picked up by liquid filters such as group_by. For example, given the following front-matter:

_test_collection/index.adoc

---
category: test
---

and the following Liquid code:

{% assign objects = site.test_collection | group_by: "category" %}

objects will have a nil value. This pull request fixes that by not deleting the category and tag properties when merging them into categories and tags, respectively.

[mojavelinux]

The category property is being deleted because it's treated as deprecated. A page can have multiple categories, so the plugin fixes this for you by promoting it to the categories array.

However, I can see how this can be limiting if you want to use it for grouping the collection. In theory, it should be possible to use the first category from the categories array for this purpose:

{% assign objects = site.test_collection | group_by: "categories[0]" %}

However, there seems to be a bug in Jekyll that is preventing this expression from working.

Here's what I'd be willing to do. Instead of deleting the category property, I'll just synchronize it with the first entry in the categories collection (which would effectively leave it untouched if it's defined in your example).

I'll update the PR and also add a test.

[mojavelinux]

I also changed the code to prepend the singular entry instead of appending it.

Let me know if PR #168 works for you.

[tyxchen]

@mojavelinux The code looks like it should work. Thanks so much!

Regarding using the first entry in the categories array in group_by, I believe Jekyll only supports using a name for the property to group, so it wouldn't recognize array indices, etc. Hope that helps.

[mojavelinux]

Regarding using the first entry in the categories array in group_by, I believe Jekyll only supports using a name for the property to group, so it wouldn't recognize array indices, etc.

Exactly my observation. I still consider this a bug in Jekyll because I think it should be possible. Liquid has a syntax for it. It's just that Jekyll is just not interpreting it correctly.