Force WordPress to use cropped intermediates for cropped image_sizes to maintain aspect ratios.

wordpress-force-cropped-intermediates.php

<?php
/* Force wp_get_attachment_image_src to always pick a cropped intermediate size.
 * If we define a sequence of srcset-friendly image_sizes like this:
 *   add_image_size('gallery',   1000, 750, true);
 *   add_image_size('gallery_1',  707, 530, true);
 *   add_image_size('gallery_2',  500, 375, true);
 * then WordPress might pick the image's original, _uncropped_, size, which
 * might have a wrong aspect ratio. To limit wp_get_attachment_image() to 
 * cropped intermediates with the right aspect ratio only, we have to manually
 * check the availability of the files.
 */

add_filter('wp_get_attachment_image_src', function ($image, $attachment_id, $size, $icon ) {
    global $_wp_additional_image_sizes; // let's hope this doesn't disappear
    // if size is given as array ([width, height]), bail out early
    if (is_array($size)) {
        return $image;
    }
    // if requested size is not cropped, bail out early
    if (!$_wp_additional_image_sizes[$size]['crop']) {
        return $image;
    }
    // get 'suffixed' size names
    $candidates = array_filter($_wp_additional_image_sizes, function ($key) use ($size) {
        return substr($key, 0, strlen($size)) === $size;
    }, ARRAY_FILTER_USE_KEY);
    foreach ($candidates as $ck => $cv) {
        $image_try = image_get_intermediate_size($attachment_id, $ck);
        // return the first match - make sure that sizes are appropriately named / sorted
        if ($image_try !== false) {
            // return in weird array format
            return [$image_try['url'], $image_try['width'], $image_try['height'], 1];
        }
    }
}, 4, 10);