I think that usernames like this should be blocked by titleblacklist at meta, and it becomes a matter of just capturing the terms to protect.

• WP: / Wikipedia:
• WS: / Wikisource:
• Wikt: / Wiktionary
• WN: / Wikinews:
• WQ: / Wikiquote
• C: / Commons:
• WV: / Wikiversity:
• Voy: / Wikivoyage:
• Project:

Please add them here or on [[m:Talk:Blacklist]]

General question, is there value in preventing the colon from being part of a username, though it is probably too late to make such a change. :-(

In T98757#1278184, @Billinghurst wrote:

I think that usernames like this should be blocked by titleblacklist at meta, and it becomes a matter of just capturing the terms to protect.

That won't scale unfortunately. For example, Benutzer:Foo is valid on enwiki, but invalid on dewiki (or any German project). This applies to any localized namespace or whenever interwiki prefixes change.

General question, is there value in preventing the colon from being part of a username, though it is probably too late to make such a change. :-(

That would be the best solution IMO.

Change 210257 had a related patch set uploaded (by Legoktm):
Add ':' to $wgInvalidUsernameCharacters

https://gerrit.wikimedia.org/r/210257

Fair point. So in the reality space

• How many usernames do we currently have that have colons in the usernames?
• Will this change just effect new accounts?
• Is this considered a breaking change?

In T98757#1278375, @Billinghurst wrote:

• How many usernames do we currently have that have colons in the usernames?

MariaDB [centralauth_p]> SELECT count(*) FROM `globaluser` WHERE gu_name LIKE '%:%';
 ---------- 
| count(*) |
 ---------- 
|    12315 |
 ---------- 

<legoktm> Glaisher: 12428 accounts actually :)
<legoktm> I guess there are 100ish suppressed accounts with : in their usernames

• Will this change just effect new accounts?

Yes.

• Is this considered a breaking change?

Existing accounts are not effected so no, I guess.

The general case of the problem is that a formerly valid username can be made invalid by later events (usually code upgrades). I'm not sure how wise it is to chase individual subcases.

Why are namespace names prevented in usernames in the first place?

Change 210257 merged by jenkins-bot:
Add ':' to $wgInvalidUsernameCharacters

https://gerrit.wikimedia.org/r/210257

In T98757#1280764, @Nemo_bis wrote:

The general case of the problem is that a formerly valid username can be made invalid by later events (usually code upgrades). I'm not sure how wise it is to chase individual subcases.

Yup, we still have to be wary of code changes. But this means configuration changes shouldn't affect the validity of usernames.

Why are namespace names prevented in usernames in the first place?

git blame points to @brion who committed https://www.mediawiki.org/wiki/Special:Code/MediaWiki/11679.