I have an XWiki on 4.1.4 (might reproduce for other versions as well but I haven't tested) which I want to upgrade to 5.2.1, I take the following steps:
1/ I upgrade the war, restart
2/ I go on the wiki, I get the distribution wizard, I repair the 4.1.4 version of org.xwiki.enterprise:xwiki-enterprise-ui (the default UI in 4.1.4) - see in the attachment the repair log
3/ I am proposed to install the default ui for 5.2 (for a xwiki-enterprise-common)
4/ get the plan in the attached file, I click ok
I get a lot of conflicts for standard pages which I haven't modified at all, and which seem to not be part of any extension, since, in the conflict UI, I don't have the option to compare with the previous version, I only have current version and new version. These pages are (potentially not very precise list, just to get an idea):
- XWiki.AttachmentSelector, the entire Stats space, Main.MessageSenderMacro, XWiki.UserDirectoryLivetableResults, Main.UserDirectory, ColorThemes standard, ColorThemes.WizardWebColors, Template Provider, XWikiClasses, XWiki.WebHome, XWiki.SharePage, XWiki.RequestsStatus, XWikiClassSheet, XWiki.ClassTemplate, XWiki.WebPrefs, Main.Welcome, Main.Spaces, Main.RSS.
From what we investigated, the reason for this behaviour is that these pages are all in the org.xwiki.enterprise:xwiki-enterprise-ui module itself in 4.1.4, not in an application which is a dependency of it, and that this application does not upgrade to anything in version 5.2.1, the default 5.2.1 ui is not an alias of the ui of 4.1.4.
This issue is a pain because there are quite a bunch of clicks to be clicked through the distribution wizard to upgrade a 4.1.4 wiki, a lot many more than needed wrt the pages that were modified from the standard distribution (e.g. on a wiki where we only changed preferences and created a couple of apps with app within minutes, the upgrader will have to click at least 30 times, not even knowing which option would be wiser to choose because they don't understand why there is a conflict on that page...).