Image loading optimization improvements for 6.4

[joemcgill]

WordPress 6.3 included many improvements to the way resource loading is handled for images and iframes, by improving the heuristics for when to automatically add lazy-loading and adding support for setting fetchpriortiy="high" on the likely LCP image. See: https://make.wordpress.org/core/2023/07/13/image-performance-enhancements-in-wordpress-6-3/ for details.

This overview ticket is to further improve the functionality added in 6.3 for the 6.4 release.

Related tickets

• Fetch priority and lazy loading attributes not applying correctly in block themes
• Fix shortcode output not receiving image (and other) optimizations
• Integrate decoding="async" logic into wp_get_loading_optimization_attributes()
• Introduce filter to modify/override attributes returned by wp_get_loading_optimization_attributes()
• Enhance wp_get_loading_optimization_attributes() to support arbitrary context values
• Twenty Twenty-Two: Header image missing dimension attributes
• Make it easier to override default loading optimizations

[mukeshpanchal27]

Added newly open ticket Core-59256 by @felixarntz cc. @eclarke1

[eclarke1]

@joemcgill is this [Type] Overview issue a duplication of this one #766 ? If so, could we consolidate these perhaps?

[westonruter]

@eclarke1 I don't think so, as #766 is specifically about database autoloading, whereas this issue is about optimizing image loading.

[joemcgill]

@westonruter is correct. I've updated the title to be more clear.

[mukeshpanchal27]

Core-58894 get committed: https://core.trac.wordpress.org/changeset/56612
Core-59256 get committed: https://core.trac.wordpress.org/changeset/56613

Core-58895 is punt to 6.5 so i will remove it from the list.

[felixarntz]

@mukeshpanchal27 I don't think https://core.trac.wordpress.org/ticket/58895 should have been punted. I believe that happened without involving any of the contributors active on that ticket? cc @joemcgill who mentioned the other day (if I remember correctly) that either this won't actually require any work, or he may be able to get a PR ready very quickly. So I think this should come back to 6.4.