This will likely just involve checking to see if the diff parameter is set as if the string value is not accepted the latest diff is shown instead.

Change 894710 had a related patch set uploaded (by JayCano; author: JayCano):

[mediawiki/extensions/CheckUser@master] WIP: Display "Show IP" buttons when using diff keywords

https://gerrit.wikimedia.org/r/894710

Change 894710 merged by jenkins-bot:

[mediawiki/extensions/CheckUser@master] Display "Show IP" buttons when using diff keywords

https://gerrit.wikimedia.org/r/894710

Hopefully the testing process is clear from the task description, but let me know if not.

In case it's of interest, I tested as in the task description, and also modified the diff param in the URL directly to test the keywords (prev, cur, next), an int ID, an invalid string and empty string (since those generate a diff page too).

I tried various different combinations of diff and oldid and saw that the temporary username always had a "Show IP" link next to it.

I did notice that when viewing an old revision using only the oldid parameter the temporary user that is displayed did not have the link (see below). I don't know if we wanted it to. I haven't found a phab ticket for this. Should I raise a separate one? @Tchanders @Niharika?

(Example from dewiki beta: https://de.wikipedia.beta.wmflabs.org/w/index.php?title=Benutzer:*Unregistered_2798&oldid=30829)

Python code to generate combinations:

combs = [964, 984, "next", "prev", "curr", "", False]
for comb in list(itertools.product(combs, combs)):
    "http://localhost:8080/w/index.php?title=Main_Page{}{}".format("&diff={}".format(comb[0]) if comb[0] != False else "", "&oldid={}".format(comb[1]) if comb[1] != False else "")

Test environment: Local docker CheckUser 2.5 (0b5ffbd) 07:38, 13 March 2023.

There is a task for this which is T331008 which should cover it not being shown if oldid is present.

Thanks @Dreamy_Jazz. @dom_walden would T331008 cover it?

In T331007#8695313, @Niharika wrote:

Thanks @Dreamy_Jazz. @dom_walden would T331008 cover it?

Yep. I didn't see that, thanks!