Filter for do_shortcode_tag()

[danielbachhuber]

As a WordPress developer with a ​collection of shortcodes, I want to include some standard JavaScript every time a shortcode in my collection is run.

In ​this pull request, I had to create a standard callback for all shortcodes in order to run wp_enqueue_script(). If I could filter the return value for do_shortcode_tag(), I could still enqueue my scripts, as well as modify the output of the shortcode.

[bobbingwide]

I had similar requirements.

1. Where I wanted to do some generic processing based on the values of shortcode attributes.
2. Where I wanted to post process the shortcode output: to support pagination
3. And whatever I need to do to appease shortcake when I enqueue jQuery and CSS

Having already implemented all my shortcodes using the same handler
it was easy for me to add the new filter functions for 1. and 2.
I don't know how to do 3. yet. :-)

See ​http://www.oik-plugins.com/oik_api/bw_shortcode_event/

You may also want to look at #32445:3
where Nacin proposes rewriting the shortcode API to use hooks under the hood.

Perhaps if do_shortcode_tag() or do_shortcode() were pluggable then we'd be able to do all sorts of interesting things.

Maybe the function to invoke in the preg_replace_callback(,do_shortcode_tag, ) calls could be determined using a filter.

Let's hope this requirement gets considered in the shortcode roadmap.

[flixos90]

32790.diff​ introduces the do_shortcode_tag filter to allow filtering the shortcode output. This also allows us, in combination with 38506, to cache expensive shortcodes.

I also removed a bit of repetitive code before to only handle what's different between the two if-clauses (namely whether $content is passed to the shortcode callback or not).

[pento]

32790.diff​ looks good. Just add some unit tests, and we're good to go! :-)

[flixos90]

32790.2.diff​ adds unit tests for the filter.

[pento]

In 38713:

Shortcodes: Add a do_shortcode_tag filter.

The addition of the pre_do_shortcode_tag in [38506] allows plugins to short-circuit the shortcode execution process, which is particularly helpful for caching expensive shortcodes.

The do_shortcode_tag is the corresponding part of that system - when a shortcode hasn't been executed previously, there needs to be a clean method of populating the cache.

Props flixos90.
Fixes #32790.