This commit adds support for filtering for topics in specific
subcategories via the categories filter query language.
For example: `category:documentation:admins` will filter for topics and
subcategory topics in
the category with slug "admins" whose parent category has the slug
"documentation".
The `=` prefix can also be used such that
`=category:documentation:admins` will exclude subcategory topics of the
category with slug "admins" whose parent category has the slug
"documentation".
On the `/filter` route, the categories filtering query language is now
supported in the input per the example provided below:
```
category:bug => topics in the bug category AND all subcategories
=category:bug => topics in the bug category excluding subcategories
category:bug,feature => allow for categories either in bug or feature
=category:bug,feature => allow for exact categories match excluding sub cats
categories: => alias for category
```
Currently composing multiple category filters is not supported as we
have yet to determine what behaviour it should result in. For example,
`category:bug category:feature` would now return topics that are in both
the `bug` and `feature` category but it is not possible for a topic to
belong to two categories.
The following are the changes being introduced in this commit:
1. Instead of mapping the query language to various query params on the
client side, we've decided that the benefits of having a more robust
query language far outweighs the benefits of having a more human readable query params in the URL.
As such, the `/filter` route will just accept a single `q` query param
and the query string will be parsed on the server side.
1. On the `/filter` route, the tags filtering query language is now
supported in the input per the example provided below:
```
tags:bug+feature tagged both bug and feature
tags:bug,feature tagged either bug or feature
-tags:bug+feature excluding topics tagged bug and feature
-tags:bug,feature excluding topics tagged bug or feature
```
The `tags` filter can also be specified multiple
times in the query string like so `tags:bug tags:feature` which will
filter topics that contain both the `bug` tag and `feature` tag. More
complex query like `tags:bug+feature -tags:experimental` will also work.
This change sets the ground work for allowing us to filter topics list
by tags in the following ways:
1. Filter for topics that matches all tags in a given set of tags
2. Filter for topics that matches any tags in a given set of tags
3. Exclude topics that matches all tags in a given set of tags
4. Exclude topics that matches any tags in a given set of tags
Alan Guo Xiang Tan