Upgrade Ring metatables on library upgrades

This is hopefully a non-risky and better change going forward, but don't
want to rock the boat immediately after fixing one upgrade issue.

As changing the implementation of any Ring method in a current version
means it has no effect on rings created in older versions, it makes
sense to apply the new metatable to avoid this trap in the future.

This appears to work fine from an upgrade of version 24 to 28 (which
adds the Link method to Ring).

AceComm-3.0/ChatThrottleLib.lua

@@ -23,7 +23,7 @@
 -- LICENSE: ChatThrottleLib is released into the Public Domain
 --
 
-local CTL_VERSION = 29
+local CTL_VERSION = 30
 
 local _G = _G
 
@@ -113,10 +113,7 @@ function Ring:Remove(obj)
 	end
 end
 
--- Note that this is local because there's no upgrade logic for existing ring
--- metatables, and this isn't present on rings created in versions older than
--- v25.
-local function Ring_Link(self, other)  -- Move and append all contents of another ring to this ring
+function Ring:Link(other)  -- Move and append all contents of another ring to this ring
 	if not self.pos then
 		-- This ring is empty, so just transfer ownership.
 		self.pos = other.pos
@@ -201,6 +198,14 @@ function ChatThrottleLib:Init()
 		end
 	end
 
+	-- All versions need to upgrade existing rings as the metatable isn't
+	-- shared between library versions.
+
+	for _, Prio in pairs(self.Prio) do
+		setmetatable(Prio.Ring, RingMeta)
+		setmetatable(Prio.Blocked, RingMeta)
+	end
+
 	-- v4: total send counters per priority
 	for _, Prio in pairs(self.Prio) do
 		Prio.nTotalSent = Prio.nTotalSent or 0
@@ -448,7 +453,7 @@ function ChatThrottleLib.OnUpdate(this,delay)
 	-- Integrate blocked queues back into their rings periodically.
 	if self.BlockedQueuesDelay >= 0.35 then
 		for _, Prio in pairs(self.Prio) do
-			Ring_Link(Prio.Ring, Prio.Blocked)
+			Prio.Ring:Link(Prio.Blocked)
 		end
 
 		self.BlockedQueuesDelay = 0