Add `rest_base` to response objects of `wp/v2/taxonomies` and `wp/v2/types` on the REST Api

[youknowriad]

As noted by @jnylen0 on this ticket https://core.trac.wordpress.org/ticket/38439#comment:8 currently there's not a way to programmatically link the taxonomy parameters to the term endpoints or the post type items to the corresponding post endpoints.

This ticket aims to add the rest_base attribute to the corresponding endpoints.

[youknowriad]

Proposed patch

[rmccue]

Previously discussed in ​https://github.com/WP-API/WP-API/issues/1381

We want to avoid exposing the raw value of rest_base in favour of exposing links that use them. Exposing the raw value encourages manual URL building, but we're trying to heavily encourage using the URLs. This may change based on #38439 however.

[jnylen0]

Here's one example of a link that is currently missing:

• The note post type supports categories: ​https://nylen.io/blog/wp-json/wp/v2/taxonomies/category
• How do I get items of the note post type? (Its rest_base is notes but there's no way to tell that from here)

Once taxonomies are added to post types in #38438 there will be a similar situation, but in reverse: going from a post type in /wp/v2/types to its taxonomies.

[youknowriad]

Links to Post Types

[youknowriad]

Oh! I see. I added a second patch. This time I add a link to post_types on the taxonomy endpoints. @jnylen0 We can do the same on the /types endpoint when we add taxonomies.

[rachelbaker]

I am +1 for this. We should return the WP_Post_Type and WP_Taxonomy objects in these responses, and the rest_base property is a part of those objects.

[rachelbaker]

@youknowriad @jnylen0 post-type-links.patch​ looks like it may belong to another ticket?

[jnylen0]

The links patch is in response to https://core.trac.wordpress.org/ticket/38607#comment:3:

We want to avoid exposing the raw value of rest_base in favour of exposing links that use them

[jnylen0]

Given the decision in #38439, rest_base is no longer useful for building URLs. We should still add it though. Here's another example where it would be useful:

1. I'm looking at a taxonomy response e.g. /wp/v2/taxonomies/post_tag
2. I follow the collection link to find some interesting terms in this taxonomy
3. I want to add one of these terms to a post. Which property name do I use?

In step 3 I want the taxonomy's rest_base, but it's not available. Currently the only way I see to get it is by looking at the last piece of the collection URL.

[jnylen0]

Refreshed patch for rest_base

[jnylen0]

38607.diff​ is rest-base.patch​ from @youknowriad, refreshed against latest trunk. Let's get this simple and helpful change in 4.7.

[joehoyle]

Updated patch with schema type => string fix, and also used the $base vars to account for rest_base not existing on the post type / taxonomy.

[joehoyle]

In 39191:

REST API: Add rest_base to response objects of wp/v2/taxonomies and wp/v2/types

Though we have the _links.collection available, having this value can be useful to know post type / taxonomy urls if you need to build them another way.

Props youknowriad, jnylen0.
Fixes #38607.