`imagecropauto()` not working with transparent background

Description

The following code:

<?php
$gdImage = imagecreatetruecolor(100,100);
imagesavealpha($gdImage, true);
imagefill($gdImage, 0, 0, imagecolorallocatealpha($gdImage, 0, 0, 0, 127));
// imagepng($gdImage, '/tmp/image_transparent.png');
$result = imagecropauto($gdImage, IMG_CROP_TRANSPARENT);
var_dump($result); // object(GdImage)#2 (0) { }
// imagepng($result, '/tmp/image_black.png');

Resulted in this output:

object(GdImage)#2 (0) { }

But I expected this output instead:

bool(false)

Docs at https://www.php.net/manual/en/function.imagecropauto.php are saying:

If the complete image was cropped, imagecrop() returns false

And this should be the case here IMO.

When doing the same with white background, it works as expected:

<?php
$gdImage = imagecreatetruecolor(100,100);
imagesavealpha($gdImage, true);
imagefill($gdImage, 0, 0, imagecolorallocate($gdImage, 255, 255, 255));
// imagepng($gdImage, '/tmp/image_white.png');
$result = imagecropauto($gdImage, IMG_CROP_WHITE);
var_dump($result); // bool(false)

PHP Version

PHP 8.3.1

Operating System

Kubuntu 22.04

Commencez par exécuter l’extrait PHP fourni avec IMG_CROP_TRANSPARENT et comparez-le au cas IMG_CROP_WHITE sur des images 100x100 entièrement transparentes et entièrement blanches. Suivez le point d’entrée imagecropauto() et ajoutez une couverture pour le cas transparent ; le travail est terminé lorsqu’une image transparente entièrement recadrée renvoie false, conformément au comportement documenté.