Fix from #9179

Fix from PathOfBuildingCommunity/PathOfBuilding#9179

Author: LocalIdentity

spec/System/TestItemMods_spec.lua

@@ -220,4 +220,40 @@ describe("TetsItemMods", function()
 		assert.are_not.equals(120, build.calcsTab.mainOutput.Armour)
 		runCallback("OnFrame")
 	end)
+	
+	t("Heralds apply exposure with Heraldry", function()
+		build.itemsTab:CreateDisplayItemFromRaw([[
+			New Item
+			Razor Quarterstaff
+			Quality: 0
+		]])
+		build.itemsTab:AddDisplayItem()
+		build.skillsTab:PasteSocketGroup("Arc 20/0 Default  1\nHerald of Thunder 20/0 Default  1\n")
+		runCallback("OnFrame")
+
+		assert.are.equals(0.5, build.calcsTab.calcsOutput.LightningEffMult)
+
+		build.configTab.input.customMods = [[
+		Nearby Enemies have Lightning Exposure while you are affected by Herald of Thunder
+		]]
+		build.configTab:BuildModList()
+		runCallback("OnFrame")
+
+		assert.are.equals(0.6, build.calcsTab.calcsOutput.LightningEffMult)
+	end)
+
+	it("Enemy self curse effect", function()
+		build.skillsTab:PasteSocketGroup("Arc 20/0 Default  1\nConductivity 22/0 Default  1\n")
+		runCallback("OnFrame")
+
+		assert.are.equals(0.8, build.calcsTab.calcsOutput.LightningEffMult)
+
+		build.configTab.input.customMods = [[
+		Nearby Enemies have 20% increased Effect of Curses on them
+		]]
+		build.configTab:BuildModList()
+		runCallback("OnFrame")
+
+		assert.are.equals(0.68, build.calcsTab.calcsOutput.LightningEffMult)
+	end)
 end)

src/Modules/CalcPerform.lua

@@ -434,10 +434,19 @@ local function determineCursePriority(curseName, activeSkill)
 	return basePriority + socketPriority + slotPriority + sourcePriority
 end
 
-local function applyEnemyModifiers(actor)
-	-- Process enemy modifiers
+local function applyEnemyModifiers(actor, clearCache)
+	if clearCache or not actor.appliedEnemyModifiers then
+		actor.appliedEnemyModifiers = { }
+	end
+	local cache = actor.appliedEnemyModifiers
+	local enemyDB = actor.enemy.modDB
 	for _, value in ipairs(actor.modDB:Tabulate(nil, nil, "EnemyModifier")) do
-		actor.enemy.modDB:AddMod(modLib.setSource(value.value.mod, value.value.mod.source or value.mod.source))
+		local mod = value.value and value.value.mod
+		if mod and not cache[mod] then
+			local source = mod.source or value.mod.source
+			enemyDB:AddMod(modLib.setSource(mod, source))
+			cache[mod] = true
+		end
 	end
 end
 
@@ -447,6 +456,9 @@ local function doActorMisc(env, actor)
 	local enemyDB = actor.enemy.modDB
 	local output = actor.output
 	local condList = modDB.conditions
+	
+	-- Process enemy modifiers
+	applyEnemyModifiers(actor)
 
 	-- Add misc buffs/debuffs
 	if env.mode_combat then
@@ -1021,11 +1033,11 @@ function calcs.perform(env, skipEHP)
 	output.WarcryPower = modDB:Override(nil, "WarcryPower") or modDB:Sum("BASE", nil, "WarcryPower") or 0
 	modDB.multipliers["WarcryPower"] = output.WarcryPower
 
-	applyEnemyModifiers(env.player)
+	applyEnemyModifiers(env.player, true)
 	if env.minion then
-		applyEnemyModifiers(env.minion)
+		applyEnemyModifiers(env.minion, true)
 	end
-	applyEnemyModifiers(env.enemy)
+	applyEnemyModifiers(env.enemy, true)
 
 	local minionTypeCount, ammoTypeCount, grenadeTypeCount = 0, 0, 0
 	local minionType, ammoType, grenadeType = { }, { }, { }