casemapping: support rfc1459/rfc1459-strict

[ghost]

This was discussed some in IRC, but it would be nice if ergo supported rfc1459 and rfc1459-strict casemapping as well.

Docs: Horse Docs

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Notes: InspIRCd and UnrealIRCd both seem to also default to ascii like ergo. (based on GitHub code search)

Libera (the largest IRC network) uses rfc1459. I imagine most of the top 10 do.

chatlogs

20:31:41 <xnaas> Yes, but my question is really: can ergo support rfc1459 (and rfc1459-strict) and should one of those be the default?
20:32:07 <@slingamn> i think my answers would be "potentially, but why would we want to?" and "no"
20:32:29 <@slingamn> the behavior we implement is a de facto standard and we publish an 005 token describing it
20:32:38 <xnaas> to match what users expect if other IRC networks already do so, mostly
20:33:04 <xnaas> Can say one of my users was very shocked to see someone could take {their_nick} when they had [their_nick] already. :P
20:34:07 <@slingamn> hmm
20:34:59 <xnaas> I'm checking InspIRCd and UnrealIRCd which dwarf ergo by raw server count. I know Libera uses rfc1459.
20:35:58 <xnaas> (And Freenode before it)
20:36:01 <@slingamn> i think it's not a clear user expectation at this point
20:36:09 <@slingamn> you can open an issue...i think dan might have thoughts
20:37:10 <xnaas> looks like InspIRCd and UnrealIRCd both also default to ascii
20:37:37 <xnaas> But I'll have to check the top 10 now :P https://netsplit.de/networks/top10.php
20:37:38 -@ErgoBot- IRC Networks - Top 10 in the annual comparison
20:38:29 <@slingamn> i would guess that most large networks use rfc1459
20:38:45 <@slingamn> but i would also guess that the distinction is important to very few people
20:39:10 <@dan> I’d rather default to ascii, easier for new client authors to implement imo and more appropriate for newer networks, but ye smol distinction
20:39:27 <@slingamn> ohai dan
20:39:33 <@dan> haihai
20:40:25 <@slingamn> dan: we could open a ticket to support rfc1459 and/or rfc1459-strict, and make it incompatible with PRECIS (if you have PRECIS enabled then you must use CASEMAPPING=ascii)
20:40:37 <@slingamn> but, i don't think it's much of a priority
20:40:49 * xnaas can definitely open an issue and you can comment "PRs welcome" 😉
20:40:55 * xnaas knows how FOSS works
20:40:57 <xnaas> 😉
20:41:02 <@slingamn> it would also create some terminological confusion because the config key that controls utf8mapping is named 'casemapping', lol
20:41:11 <@dan> if you’d like to maintain it then totally open to having it ;D
20:41:16 <@dan> ehe

[slingamn]

This would be a fun thing to do, in keeping with our overall "reference implementation" mandate, and pretty easy. We'd basically just need to add them here:

ergo/irc/strings.go

Lines 49 to 63 in c67835c

	const (
	// "precis" is the default / zero value:
	// casefolding/validation: PRECIS + ircd restrictions (like no *)
	// confusables detection: standard skeleton algorithm
	CasemappingPRECIS Casemapping = iota
	// "ascii" is the traditional ircd behavior:
	// casefolding/validation: must be pure ASCII and follow ircd restrictions, ASCII lowercasing
	// confusables detection: none
	CasemappingASCII
	// "permissive" is an insecure mode:
	// casefolding/validation: arbitrary unicodes that follow ircd restrictions, unicode casefolding
	// confusables detection: standard skeleton algorithm (which may be ineffective
	// over the larger set of permitted identifiers)
	CasemappingPermissive
	)

and then add corresponding cases to casefoldWithSetting and skeleton (precis and permissive would use the real skeletonization, ascii and the two new options would use the identity function).

[slingamn]

Oh, and the 005 token would have to be made conditional:

ergo/irc/config.go

Line 1625 in c67835c

isupport.Add("CASEMAPPING", "ascii")