Featured image performance

[rclations]

The Problem

We're running a filter on post body content that checks if the post starts with an image, and if that image matches the post's featured image, removes the content from the post display (to prevent duplicate displays of that featured image).

The issue is the method we're running that check. Currently, we're getting the source for the image in the post body, then running a very slow query to lookup that image's ID in the database. This type of query/logic cannot continue to exist for performance reasons.

The solution

Every image inserted by the media editor should have a wp-image-## class on it, where ## is the id of the media file. By pulling this ID out with regex, we can achieve the same effect, but avoid expensive queries.

Potential Downsides

If the html for the image has been manipulated or inserted by hand so that it does not include the wp-image-## class, then this obviously won't work.

[benlk]

Tests are failing on this, for a test that seems relevant:

1) PostTemplatesTestFunctions::test_insert_image_no_thumb
Failed asserting that two strings are equal.
--- Expected
+++ Actual
@@ @@
-'<h2>Headings</h2>
+'<p><img src="http://example.org/wp-content/uploads/2017/01/cat-771x510.jpg" alt="1559758083_cef4ef63d2_o" width="771" height="475" class="alignnone size-large" /></p>
+<h2>Headings</h2>
 <p>Integer posuere erat a ante venenatis dapibus posuere velit aliquet. Sed posuere consectetur est at lobortis. Nulla vitae elit libero, a pharetra augue. Fusce dapibus, tellus ac cursus commodo, tortor mauris condimentum nibh, ut fermentum massa justo sit amet risus. Donec sed odio dui.</p>'
/tmp/wordpress/src/wp-content/themes/Largo/tests/inc/test-post-templates.php:79

[rclations]

okay so the test we had wasn't utilizing the wp-image-[id] class that's now required for this to work. Last commit updates the test to include this