Prevent WordPress from cropping GIF files

Unsetting sizes can normally be done easily via intermediate_image_sizes_advanced hook. The only problem is, there is only the $sizes array available, so this sufficient for a general level, but not if you want to do this conditionally. The information needed to do it conditionally can be gathered with debug_backtrace – debug_backtrace is performance-wise somewhat expensive though. Anyhow, I imagine it could be done like shown below:

add_action(
    'intermediate_image_sizes_advanced',
    'wpse162413_unset_sizes_if_gif'
);
function wpse162413_unset_sizes_if_gif( $sizes ) {
    // we're only having the sizes available
    // we're using debug_backtrace to get additional information
    $dbg_back = debug_backtrace();
    // scan $dbg_back array for function and get $args
    foreach ( $dbg_back as $sub ) {
        if ( $sub[ 'function'] == 'wp_generate_attachment_metadata' ) {
            $args = $sub[ 'args' ]; 
        }
    }
    // attachment id
    $att_id       = $args[0];
    // attachment path
    $att_path     = $args[1];
    // split up file information
    $pathinfo = pathinfo( $att_path );
    // if extension is gif unset sizes
    if ( $pathinfo[ 'extension' ] == 'gif' ) {
        // get all intermediate sizes
        $intermediate_image_sizes = get_intermediate_image_sizes();
        // loop trough the intermediate sizes array
        foreach ( $intermediate_image_sizes as $size ) {
            // unset the size in the sizes array
            unset( $sizes[ $size ] );
        }
    }
    // return sizes
    return $sizes;
}