The InlineComments should support "@"-style user mentions. That means the following:
- If a user types "@" in a comment (either a new comment or a reply), then an alphanumeric character afterwards, an autocompletion dropdown should appear, letting the user select from the set of usernames on the wiki that match what the user has typed.
- If the user selects one of those usernames from the dropdown, the username should appear, highlighted or bolded in some way.
- Once a comment is saved, the username(s) in that comment should still be highlighted or bolded when the comment is displayed.
- Any users who are "mentioned" in an inline comment should get notified, via the Echo extension.
There seem to be three main ways to do this: an entirely custom solution, a solution involving a 3rd-party autocompletion JS library, or via the "@"-autocompletion feature in the DiscussionTools extension, which in turn relies on VisualEditor. If one were to go with the third approach, it would mean that every textarea in InlineComments would in reality be a VisualEditor input; if that were done, it may make sense to use JS or CSS to hide the VE toolbar from users. (It would also mean that three other MW extensions would be required for the InlineComments user mentions feature to work fully: VisualEditor, DiscussionTools and Echo.)