addon-compat: unregister ShaguTweaks libpredict's backported TBC events

ShaguTweaks' libpredict sender frame (ShaguTweaksPredictionSender) registers
TBC-era events alongside its vanilla ones — COMBAT_LOG_EVENT_UNFILTERED and
UNIT_SPELLCAST_START/STOP/FAILED/INTERRUPTED/SENT (libpredict.lua:342-347). In
stock 1.12.1 those never fire, so registering them was a harmless no-op and only
the vanilla SPELLCAST_* path ran. ClassicAPI now backports those events, so
libpredict's TBC branches fire too and double-process cast/heal predictions.

Unregister the six TBC events on libpredict.sender once ShaguTweaks loads,
restoring vanilla-only behavior. Guarded on the addon existing and the
libpredict table being present.

AddOns/!!!ClassicAPI/Util/AddOnCompat.lua

@@ -43,3 +43,18 @@ end
 if C_AddOns.DoesAddOnExist("SpecialTalentUI") then
     EventUtil.ContinueOnAddOnLoaded("SpecialTalentUI", CAPI_ApplyStandardColorGlobals)
 end
+
+-- ShaguTweaks libpredict register's TBC events that ClassicAPI backports.
+if C_AddOns.DoesAddOnExist("ShaguTweaks") then
+    EventUtil.ContinueOnAddOnLoaded("ShaguTweaks", function()
+        local libp = ShaguTweaks.libpredict
+        if libp then
+            libp.sender:UnregisterEvent("COMBAT_LOG_EVENT_UNFILTERED")
+            libp.sender:UnregisterEvent("UNIT_SPELLCAST_START")
+            libp.sender:UnregisterEvent("UNIT_SPELLCAST_STOP")
+            libp.sender:UnregisterEvent("UNIT_SPELLCAST_FAILED")
+            libp.sender:UnregisterEvent("UNIT_SPELLCAST_INTERRUPTED")
+            libp.sender:UnregisterEvent("UNIT_SPELLCAST_SENT")
+        end
+    end)
+end

AddOns/!!!ClassicAPI/Util/CallbackRegistry.lua

@@ -26,10 +26,17 @@ local function GenerateClosure(func, ...)
     for i = 1, boundN do bound[i] = arg[i] end
     return function(...)
         local callN = arg.n
-        local merged = {}
-        for i = 1, boundN do merged[i] = bound[i] end
-        for i = 1, callN do merged[boundN + i] = arg[i] end
-        return func(unpack(merged, 1, boundN + callN))
+        -- Pass the first bound arg (the owner, always bound[1] here) explicitly
+        -- and everything else as the unpacked tail. Merging bound + call into
+        -- one table and unpacking THAT collapses the vararg count on this Lua
+        -- 5.0 build when a hole lands right after a present element — same trap
+        -- fixed in TriggerEvent's Function branch. Keeping owner out of the
+        -- unpacked table keeps a leading-nil payload inside the vararg tail.
+        local rest = {}
+        local restN = 0
+        for i = 2, boundN do restN = restN + 1; rest[restN] = bound[i] end
+        for i = 1, callN do restN = restN + 1; rest[restN] = arg[i] end
+        return func(bound[1], unpack(rest, 1, restN))
     end
 end
 
@@ -145,11 +152,14 @@ function CallbackRegistryMixin:TriggerEvent(event, ...)
     if funcs then
         for owner, func in pairs(funcs) do
             -- Stock 3.3.5 passes the owner as the first arg so callers can
-            -- distinguish multiple registrations of the same function.
-            local n = arg.n
-            local merged = { owner }
-            for i = 1, n do merged[i + 1] = arg[i] end
-            func(unpack(merged, 1, n + 1))
+            -- distinguish multiple registrations of the same function. Pass it
+            -- explicitly with the payload as the unpacked tail. Do NOT build a
+            -- { owner, ... } table and unpack THAT: on this Lua 5.0 build,
+            -- unpacking a table whose hole lands right after a present element
+            -- (owner) into a `func(first, ...)` collapses the vararg count to 0,
+            -- silently dropping a leading-nil event payload (verified in-game
+            -- with reload's PLAYER_ENTERING_WORLD, arg1=nil arg2=1).
+            func(owner, unpack(arg, 1, arg.n))
         end
     end
 end

README.md

@@ -35,7 +35,7 @@ Full per-function reference: **[docs/API.md](docs/API.md)**.
 | [Expansion](docs/API.md#expansion) | `ClassicExpansionAtLeast`, `ClassicExpansionAtMost`, `GetClassicExpansionLevel` |
 | [Faction](docs/API.md#faction) | `C_Reputation.GetFactionDataByIndex`, `C_Reputation.GetFactionStandings`, `C_Reputation.GetLastStandingChange`, `C_Reputation.GetWatchedFactionData`, `C_Reputation.SetWatchedFactionByID`, `GetFactionIDByIndex`, `GetFactionInfoByID`, `GetFactionParentID` |
 | [Focus](docs/API.md#focus) | `ClearFocus`, `FocusUnit` |
-| [Frame](docs/API.md#frame) | `region:SetPoint("point")` (one-arg form), `region:SetSize`, `region:GetSize`, `region:IsMouseOver`, `region:GetRect`, `region:IsDragging`, `frame:SetShown`, `frame:SetResizeBounds`, `frame:HookScript`, `frame:IsEventRegistered`, `frame:GetEffectiveAlpha` |
+| [Frame](docs/API.md#frame) | `region:SetPoint("point")` (one-arg form), `region:SetSize`, `region:GetSize`, `region:IsMouseOver`, `region:GetRect`, `region:IsDragging`, `frame:SetShown`, `frame:SetResizeBounds`, `frame:HookScript`, `frame:IsEventRegistered`, `frame:GetEffectiveAlpha`, `frame:SetAttribute`, `frame:SetAttributeNoHandler`, `frame:ClearAttribute`, `frame:GetAttribute`, `OnAttributeChanged` (script), `SetModernScriptArgs`, `GetModernScriptArgs` |
 | [FriendList](docs/API.md#friendlist) | `C_FriendList.IsWhoQueryPending`, `C_FriendList.SendWhoQueryByName` |
 | [GameObject](docs/API.md#gameobject) | `C_GameObjectInfo.GetGameObjectInfoByID`, `C_GameObjectInfo.RequestLoadGameObjectByID`, `ClosestGameObjectPosition` |
 | [Glue](docs/API.md#glue) | `C_Glue.IsOnGlueScreen` |

docs/API.md

@@ -165,6 +165,7 @@ build instructions.
   - [`frame:IsEventRegistered(event)`](#frameiseventregisteredevent)
   - [`frame:GetEffectiveAlpha()`](#framegeteffectivealpha)
   - [`frame:SetAttribute` / `SetAttributeNoHandler` / `ClearAttribute` / `GetAttribute` (+ unit-frame mouseover)](#framesetattributename-value--framesetattributenohandlername-value--frameclearattributename--framegetattribute)
+  - [`SetModernScriptArgs(enable)` / `GetModernScriptArgs()`](#setmodernscriptargsenable--getmodernscriptargs)
 
 - [FriendList](#friendlist)
   - [`C_FriendList.SendWhoQueryByName(name)`](#c_friendlistsendwhoquerybynamename)
@@ -3923,6 +3924,40 @@ per-frame handler slot for this one name (1.12 frames are never destroyed, so
 the slot never goes stale). Recursion-guarded, so a handler may itself call
 `SetAttribute`.
 
+### `SetModernScriptArgs(enable)` / `GetModernScriptArgs()`
+
+Global toggle (not a frame method) for **modern positional script arguments**.
+Vanilla always invokes a frame-script handler with **zero** Lua arguments — the
+handler reads `this` / `arg1..argN` / `event` as globals. With this enabled, every
+handler additionally receives its values as real positional arguments, so modern
+addon ports written as `function(self, delta) … end` work unmodified:
+
+- most scripts: `(self, arg1..argN)` — e.g. `OnMouseWheel(self, delta)`,
+  `OnClick(self, button)`, `OnValueChanged(self, value)`, `OnUpdate(self, elapsed)`.
+- `OnEvent`: `(self, event, arg1..argN)`.
+
+It's purely **additive** — the `this` / `arg1` / `event` globals are still set, so
+vanilla-style handlers keep working; a handler declaring no parameters just ignores
+the extras. `SetModernScriptArgs(enable)` sets the state and returns it;
+`GetModernScriptArgs()` returns the current state.
+
+**Default OFF (opt-in).** It reimplements the tail of the engine's hottest Lua
+path (the runner that fires for every `OnUpdate`, every frame), so it stays off
+unless you ask for it; while off the dispatch path is exactly vanilla. Enable it
+once at load if your addon relies on the modern handler signature.
+
+```lua
+SetModernScriptArgs(true)   -- returns true
+
+local f = CreateFrame("Frame")
+f:EnableMouseWheel(true)
+f:SetScript("OnMouseWheel", function(self, delta)
+    -- `self` and `delta` are bound; `this` / `arg1` still work too
+end)
+
+GetModernScriptArgs()       -- true
+```
+
 ## FriendList
 
 ### `C_FriendList.SendWhoQueryByName(name)`