我只想在调用特定缩略图大小时禁用srcset（例如，仅在调用完整图像大小时）。

这里有两个想法（如果我理解正确的话）：

接近#1

/**
 * Remove the srcset attribute from post thumbnails 
 * that are called with the \'full\' size string: the_post_thumbnail( \'full\' )
 *
 * @link http://wordpress.stackexchange.com/a/214071/26350
 */
 add_filter( \'post_thumbnail_size\', function( $size )
 {
     if( is_string( $size ) && \'full\' === $size )
         add_filter( 
             \'wp_calculate_image_srcset_meta\',  
              \'__return_null_and_remove_current_filter\' 
         );   
    return $size;
 } );

// Would be handy, in this example, to have this as a core function ;-)
function __return_null_and_remove_current_filter ( $var )
{
    remove_filter( current_filter(), __FUNCTION__ );
    return null;
}

the_post_thumbnail( \'full\' );

对于这种情况：

the_post_thumbnail();

方法#2

// Add a filter to remove srcset attribute from generated <img> tag
add_filter( \'wp_calculate_image_srcset_meta\', \'__return_null\' );

// Display post thumbnail
the_post_thumbnail();

// Remove that filter again
remove_filter( \'wp_calculate_image_srcset_meta\', \'__return_null\' );

不需要过滤器。最简单的解决方案如下：

// exclude any attribute you want to keep from the list
// choose any defined image size, ie. large, medium, etc
echo preg_replace( \'/(width|height|srcset|sizes)="[^"]*"/\', \'\', get_the_post_thumbnail( get_the_ID(), \'large\') );