When user rights are changed, the log usually lists the old rights and the new rights. That is useful in some cases, but other times what I really want to see is what changed, which is difficult when the information is a sentence with lists of words. More clear is what some admins so in their edit summary, saying what right was added/removed rather than just an explanation of why some change was made. Consider the following three examples from the recent en.wp log (chosen solely for illustrative purposes), listed in increasing order of readability that entails increasing amounts of work by admin with key details underlined:

• 11:47, 10 July 2017 Alex Shih (talk | contribs | block) changed group membership for Jupitus Smart from autopatrolled, extended confirmed user, new page reviewer, pending changes reviewer and rollbacker to autopatrolled, extended confirmed user, new page reviewer, pending changes reviewer, rollbacker and page mover
• 12:08, 10 July 2017 Alex Shih (talk | contribs | block) changed group membership for Seppi333 from extended confirmed user and IP block exempt to extended confirmed user, IP block exempt and template editor (Wikipedia:Requests_for_permissions/Template_editor)
• 11:06, 10 July 2017 Kudpung (talk | contribs | block) changed group membership for Steve Quinn from autopatrolled, extended confirmed user and pending changes reviewer to autopatrolled, extended confirmed user, pending changes reviewer and new page reviewer (+patroller; Requested at WP:PERM; Special:PermaLink/789904243#User:Steve Quinn (using userRightsManager))

The "+patroller" in the third is what I would like to see happen automatically.

I posted to [[:en:Village pump (technical)#Clarity of user-rights log messages]], where there was some support for the idea. I don't know the mediawiki codebase, but from grepping around in git, it appears this is formatted in LogFormatter.php getIRCActionText()