Custom image size not generated if identical to original size

[brampeerlings]

When defining a custom image size using add_image_size and uploading an image that has exactly the same dimensions of that image size, the new image size is not added. This also means that -- when adding the newly defined image size -- to the Insert Media screen using the image_size_names_choose-filter, the custom image size does not appear in the dropdown menu.

Even though I can understand why this happens from a server load / storage point of view, I feel the unexpected behaviour (to end users) is a bigger problem. An even prettier fix would be to detect the custom image size is identical to the original size and map the custom image size URL to the original file URL (e.g. through a symbolic link).

<?php
if ( function_exists( 'add_image_size' ) ) {
    add_image_size( 'project-photo', 1920, 1080, false);
}

function custom_media_sizes( $sizes ) {
    return array_merge( $sizes, array(
        'project-photo' => __( 'Project-foto' ),
    ) );
}
add_filter( 'image_size_names_choose', 'custom_media_sizes' );

[afercia]

Discussed during today's accessibility bug-scrub: not sure this issue is related to accessibility, removing the accessibility focus for now.

[antpb]

This was mentioned in the Media component meeting and we were able to reproduce the report.

• To reproduce add the provided snippet with the sizes attribute exactly matching an image available
• Upload that image
• Insert that image to a post and notice that the custom size is not available.
• Upload any other image that is not the same size
• Insert the second image into a post and notice the custom size _is_ available

We need to catch for the case of custom sizes matching the uploaded image and use the originally uploaded image for that custom size.

[antpb]

this is likely not to make it into the 6.2 milestone. This should move to 6.3 when possible.