TYPO3 Core

The class loader tries to load files of aliased classes twice if certain strange circumstances are met.

/srv/www/ and /var/www/ are mounts (not symlinks) of the same harddisk. TYPO3 is used via HTTP (Apache), document root /var/www/typo3/. TYPO3 is also used on the CLI via document root /srv/www/typo3/.

The class loading process is as follows:

1. Apache: TYPO3 gets used, writes caches.
2. CLI: TYPO3 core gets loaded, /srv/.../GeneralUtility.php is loaded.
3. Extension configuration gets loaded. Their paths are loaded from /var/... now because of the caches
4. An extension's ext_localconf.php uses t3lib_div, which is handed to the class loader.
5. Class loader sees it's an alias to GeneralUtility and tries to load that first. It calculates the path of GeneralUtility to be /var/.../GeneralUtility.php and does a require_once call on it.
6. PHP loads this file because it does not know that /srv/.../GeneralUtility.php is the same file as /var/.../GeneralUtility.php
7. Fatal error: Cannot redeclare class TYPO3\CMS\Core\Utility\GeneralUtility

While this is an obscure configuration, the fix is easy: Simply check if the class already exists before requiring the file.

I'll contribute a patch.

This error did not happen with 6.2beta4 and started with 6.2beta5, probably because of 890cdbcf4013b2c870e315cce13400f44d3304b6 (bug #55559).