Don't composer-update the old installation but the new one, i.e. run this inside of your /tmp/roundcubemail-1.5-rc
Ah. That perhaps how I managed to break my current 1.4.11 installation. Updating the Calendar and Tasklist plugs fixed that, though!
So, just to be clear, I'm trying to upgrade my 1.4.11 to the 1.5-RC version. I have untarred the complete package to /tmp/roundcubemail-1.5-rc and when I try the upgrade from that directory (./bin/installto.sh /var/www/html/webmail) it fails with the dependency error I reported previously. If I try to run the composer-update in the /tmp/roundcubemail-1.5-rc directory I get the following error:
[root@freepbx roundcubemail-1.5-rc]# php composer.phar install --no-dev
Could not open input file: composer.phar
[root@freepbx roundcubemail-1.5-rc]# ls
bin composer.json-dist index.php LICENSE program SECURITY.md temp
CHANGELOG.md composer.lock INSTALL logs public_html skins UPGRADING
composer.json config installer plugins README.md SQL vendor
[root@freepbx roundcubemail-1.5-rc]#