wp_calculate_image_srcset can unintentionally include unscaled original image

[fredrikll]

In wp-includes/media.php, wp_calculate_image_srcset seems to add the original image to the srcset string if the width is smaller than $max_srcset_image_width and if the image isn't a GIF. This isn't desirable since the original image is uncompressed and I don't even think it's intentional.

This behavior seems to have been introduced in this patch: https://core.trac.wordpress.org/changeset/35561. From what I can tell, the if statement should read like this:

if ( ! isset( $image_sizes['thumbnail']['mime-type'] ) || 'image/gif' === $image_sizes['thumbnail']['mime-type'] ) {

The current code will include the original image whenever the thumbnail IS NOT a GIF. This seems to be opposite to the desired behavior?

[johnbillion]

Thanks for the report @fredrikll and welcome. Moving this to 5.5.1 for investigation.

[khag7]

To prevent anyone from getting as confused as I did:
Change [35561] is just a refactor and better description. The logic stayed the same.

The change that introduced no srcset on gifs was slightly sooner, in [35524].

[fredrikll]

@khag7 the refactor in [35561] actually seems to be the issue. If the relevant if statement would still look like [35524], this bug would be fixed, from what I can tell.

The difference should be quite clear if one looks closer: isset( $image_sizes['thumbnail']['mime-type'] ) && 'image/gif' === $image_sizes['thumbnail']['mime-type'] versus ! isset( $image_sizes['thumbnail']['mime-type'] ) || 'image/gif' !== $image_sizes['thumbnail']['mime-type']