**Obsoleted by DFHack's item-trigger**. Itemsyndrome. Usage is given when "itemsyndrome help" is used. Updated for DFHack 0.34.11 r4. lso updated with Boltgun's changes to the assignment function.

itemsyndrome.lua

-- Checks for inventory changes and applies or removes syndromes that items or their materials have. Use "disable" (minus quotes) to disable and "help" to get help.
 
local args = {...}
 
local function printItemSyndromeHelp()
    print("Arguments (non case-sensitive):")
    print('    "help": displays this dialogue.')
    print(" ")
    print('    "disable": disables the script.')
    print(" ")
    print('    "debugon/debugoff": debug mode.')
    print(" ")
    print('    "contaminantson/contaminantsoff": toggles searching for contaminants.')
    print('    Disabling speeds itemsyndrome up greatly.')
    print('    "transformReEquipOn/TransformReEquipOff": toggles transformation auto-reequip.')
end
 
itemsyndromedebug=false
 
function processArgs(args)
    for k,v in ipairs(args) do
        v=v:lower()
        if v == "help" then printItemSyndromeHelp() return end
        if v == "debugon" then itemsyndromedebug = true end
        if v == "debugoff" then itemsyndromedebug = false end
        if v == "contaminantson" then itemsyndromecontaminants = true end
        if v == "contaminantsoff" then itemsyndromecontaminants = false end
        if v == "transformreequipon" then transformationReEquip = true end
        if v == "transformreequipoff" then transformationReEquip = false end
    end
end
 
processArgs(args)
 
local function getMaterial(item)
    local material = dfhack.matinfo.decode(item) and dfhack.matinfo.decode(item) or false
    if not material then return nil end
    if material.mode ~= "inorganic"  then
        return nil
    else
        return material.material --the "material" thing up there contains a bit more info which is all pretty important but impertinent, like the creature that the material comes from
    end
end
 
local function findItemSyndromeInorganic()
    local allInorganics = {}
    for matID,material in ipairs(df.global.world.raws.inorganics) do
        if string.find(material.id,"DFHACK_ITEMSYNDROME_MATERIAL_") then table.insert(allInorganics,matID) end --the last underscore is needed to prevent duped raws; I want good modder courtesy if it kills me, dammit!
    end
    if itemsyndromedebug then printall(allInorganics) end
    if #allInorganics>0 then return allInorganics else return nil end
end
 
local function getAllItemSyndromeMats(itemSyndromeMatIDs)
    local allActualInorganics = {}
    for _,itemSyndromeMatID in ipairs(itemSyndromeMatIDs) do
        table.insert(allActualInorganics,df.global.world.raws.inorganics[itemSyndromeMatID].material)
    end
    if itemsyndromedebug then printall(allActualInorganics) end
    return allActualInorganics
end
 
local function syndromeIsDfHackSyndrome(syndrome)
    for k,v in ipairs(syndrome.syn_class) do
        if v.value=="DFHACK_ITEM_SYNDROME" then 
            if itemsyndromedebug then print('Syndrome is DFHack syndrome, checking if creature is affected...') end
            return true 
        end
    end
    if itemsyndromedebug then print('Syndrome is not DFHack syndrome. Cancelling.') end
    return false
end
 
local function itemHasNoSubtype(item)
   return item:getSubtype()==-1
end
 
local function itemHasSyndrome(item)
    if itemHasNoSubtype(item) or not itemSyndromeMats then return nil end
    local allItemSyndromes={}
    for _,material in ipairs(itemSyndromeMats) do
        for __,syndrome in ipairs(material.syndrome) do
            if syndrome.syn_name == item.subtype.name then table.insert(allItemSyndromes,syndrome) end
        end
    end
    return #allItemSyndromes>0 and allItemSyndromes or false
end
 
local function alreadyHasSyndrome(unit,syn_id)
    for _,syndrome in ipairs(unit.syndromes.active) do
        if syndrome.type == syn_id then return true end
    end
    return false
end

local function eraseSyndrome(target,syn_id)
    for i=#target.syndromes.active-1,0,-1 do
        if target.syndromes.active[i].type==syn_id then target.syndromes.active:erase(i) end
    end
end
 
local function assignSyndrome(target,syn_id) --taken straight from here, but edited so I can understand it better: https://gist.github.com/warmist/4061959/. Also implemented expwnent's changes for compatibility with syndromeTrigger.
    if target==nil then
        return nil
    end
    if alreadyHasSyndrome(target,syn_id) then
        local syndrome
        for k,v in ipairs(target.syndromes.active) do
            if v.type == syn_id then syndrome = v end
        end
        if not syndrome then return nil end
        syndrome.ticks=1
        return true
    end
    local newSyndrome=df.unit_syndrome:new()
    local target_syndrome=df.syndrome.find(syn_id)
    newSyndrome.type=target_syndrome.id
    newSyndrome.year=df.global.cur_year
    newSyndrome.year_time=df.global.cur_year_tick
    newSyndrome.ticks=0
    newSyndrome.unk1=0
    --newSyndrome.flags=0
    for k,v in ipairs(target_syndrome.ce) do
        local sympt=df.unit_syndrome.T_symptoms:new()
        sympt.unk1=0
        sympt.unk2=0
        sympt.ticks=0
        sympt.flags=2
        newSyndrome.symptoms:insert("#",sympt)
    end
    target.syndromes.active:insert("#",newSyndrome)
    if itemsyndromedebug then
        print("Assigned syndrome #" ..syn_id.." to unit.")
    end
    return true
end
 
local function syndromeIsIndiscriminate(syndrome)
    return (#syndrome.syn_affected_class==0 and #syndrome.syn_affected_creature==0 and #syndrome.syn_affected_caste==0 and #syndrome.syn_immune_class==0 and #syndrome.syn_immune_creature==0 and #syndrome.syn_immune_caste==0)
end
 
local function creatureIsAffected(unit,syndrome)
    if syndromeIsIndiscriminate(syndrome) then
        if itemsyndromedebug then
            print("Creature is affected, checking if item is in valid position...")
        end
        return true 
    end
    local affected = false
    local unitraws = df.creature_raw.find(unit.race)
    local casteraws = unitraws.caste[unit.caste]
    local unitracename = unitraws.creature_id
    local castename = casteraws.caste_id
    local unitclasses = casteraws.creature_class
    for _,unitclass in ipairs(unitclasses) do
        for _,syndromeclass in ipairs(syndrome.syn_affected_class) do
            if unitclass.value==syndromeclass.value then affected = true end
        end
    end
    for caste,creature in ipairs(syndrome.syn_affected_creature) do
        local affected_creature = creature.value
        local affected_caste = syndrome.syn_affected_caste[caste].value --slightly evil, but oh well, hehe.
        if affected_creature == unitracename and affected_caste == castename then affected = true end
    end
    for _,unitclass in ipairs(unitclasses) do
        for _,syndromeclass in ipairs(syndrome.syn_immune_class) do
            if unitclass.value==syndromeclass.value then affected = false end
        end
    end
    for caste,creature in ipairs(syndrome.syn_immune_creature) do
        local immune_creature = creature.value
        local immune_caste = syndrome.syn_immune_caste[caste].value
        if immune_creature == unitracename and immune_caste == castename then affected = false end
    end
    if itemsyndromedebug then
        if not affected then print("Creature is not affected. Cancelling.") else print("Creature is affected, checking if item is in valid position...") end
    end
    return affected
end
 
local function getValidPositions(syndrome)
    local returnTable={AffectsHauler=false,AffectsStuckins=false,IsArmorOnly=false,IsWieldedOnly=false,OnlyAffectsStuckins=false}
    for k,v in ipairs(syndrome.syn_class) do
        if v.value:find('DFHACK') then
            if v.value=="DFHACK_AFFECTS_HAULER" then returnTable.AffectsHauler=true end
            if v.value=="DFHACK_AFFECTS_STUCKIN" then returnTable.AffectsStuckins=true end
            if v.value=="DFHACK_STUCKINS_ONLY" then returnTable.OnlyAffectsStuckins=true end    
            if v.value=="DFHACK_WIELDED_ONLY" then returnTable.IsWieldedOnly=true end
            if v.value=="DFHACK_ARMOR_ONLY" then returnTable.IsArmorOnly=true end
        end
    end
    return returnTable
end
       
local function itemIsInValidPosition(item_inv, syndrome)
    local item = getValidPositions(syndrome)
    if not item_inv then print("You shouldn't see this error! At all! Putnam f'd up! Tell her off!") return false end
    local isInValidPosition=not ((item_inv.mode == 0 and not item.AffectsHauler) or (item_inv.mode == 7 and not item.AffectsStuckins) or (item_inv.mode ~= 2 and item.IsArmorOnly) or (item_inv.mode ~=1 and item.IsWieldedOnly) or (item_inv.mode ~=7 and item.OnlyAffectsStuckins))
    if itemsyndromedebug then print(isInValidPosition and 'Item is in correct position.' or 'Item is not in correct position.') end
    return isInValidPosition
end
 
local function syndromeIsTransformation(syndrome)
    for _,effect in ipairs(syndrome.ce) do
        if df.creature_interaction_effect_body_transformationst:is_instance(effect) then return true end
    end
    return false
end
 
local function rememberInventory(unit)
    local invCopy = {}
    for inv_id,item_inv in ipairs(unit.inventory) do
        invCopy[inv_id+1] = {}
        local itemToWorkOn = invCopy[inv_id+1]
        itemToWorkOn.item = item_inv.item
        itemToWorkOn.mode = item_inv.mode
        itemToWorkOn.body_part_id = item_inv.body_part_id
    end
    return invCopy
end
 
local function moveAllToInventory(unit,invTable)
    for _,item_inv in ipairs(invTable) do
        dfhack.items.moveToInventory(item_inv.item,unit,item_inv.mode,item_inv.body_part_id)
    end
end

local function syndromeIsOnUnequip(syndrome)
    for k,v in ipairs(syndrome.syn_class) do
        if v.value:upper()=='DFHACK_ON_UNEQUIP' then return true end
    end
    return false
end
 
local function addOrRemoveSyndromeDepending(unit,old_equip,new_equip,syndrome)
	local item_inv=new_equip or old_equip
    if syndromeIsOnUnequip(syndrome) then
        if itemsyndromedebug then print('Syndrome is applied on unequip.') end
        if syndromeIsDfHackSyndrome(syndrome) and creatureIsAffected(unit,syndrome) and itemIsInValidPosition(item_inv,syndrome) then
            if not new_equip then
                assignSyndrome(unit,syndrome.id)
            else
                eraseSyndrome(unit,syndrome.id)
            end
        end    
    else
        if itemsyndromedebug then print('Syndrome is applied on equip.') end
        if syndromeIsDfHackSyndrome(syndrome) and creatureIsAffected(unit,syndrome) and itemIsInValidPosition(item_inv,syndrome) then
            if new_equip then
                assignSyndrome(unit,syndrome.id)
            else
                eraseSyndrome(unit,syndrome.id)
            end
        end
    end
end
 
eventful=require('plugins.eventful')
 
eventful.enableEvent(eventful.eventType.INVENTORY_CHANGE,5)
 
eventful.onInventoryChange.itemsyndrome=function(unit_id,item_id,old_equip,new_equip)
    local item = df.item.find(item_id)
    if not item then return false end
    local unit = df.unit.find(unit_id)
    if unit.flags1.dead then return false end
    if itemsyndromedebug then print("Checking unit #" .. unit_id) end
    local transformation = false
    if itemsyndromedebug then print("checking item #" .. item_id .." on unit #" .. unit_id) end
    local itemMaterial=getMaterial(item)
    if itemMaterial then
        for k,syndrome in ipairs(itemMaterial.syndrome) do
            if itemsyndromedebug then print("item has a syndrome, checking if syndrome is valid for application...") end
            if syndromeIsTransformation(syndrome) then
                unitInventory = rememberInventory(unit)
                transformation = true
            end
            addOrRemoveSyndromeDepending(unit,old_equip,new_equip,syndrome)
        end
    end
    local itemSyndromes = itemHasSyndrome(item)
    if itemSyndromes then
        if itemsyndromedebug then print("Item itself has a syndrome, checking if item is in correct position and creature is affected") end
        for k,syndrome in ipairs(itemSyndromes) do
            if syndromeIsTransformation(syndrome) then
                unitInventory = rememberInventory(unit)
                transformation = true
            end
            addOrRemoveSyndromeDepending(unit,old_equip,new_equip,syndrome)
        end
    end
    if itemsyndromecontaminants and item.contaminants then
        if itemsyndromedebug then print("Item has contaminants. Checking for syndromes...") end
        for _,contaminant in ipairs(item.contaminants) do
            local contaminantMaterial=getMaterial(contaminant)
            if contaminantMaterial then
                for k,syndrome in ipairs(contaminantMaterial.syndrome) do
                    if itemsyndromedebug then print("Checking syndrome #" .. k .. "on contaminant #" .. _ .. " on item #" .. item_id .. " on unit #" .. unit_id ..".") end
                    if syndromeIsTransformation(syndrome) then
                        unitInventory = rememberInventory(unit)
                        transformation =true
                    end
                    addOrRemoveSyndromeDepending(unit,old_equip,new_equip,syndrome)
                end
            end
        end
    end
    if transformation and transformationReEquip then dfhack.timeout(2,"ticks",function() moveAllToInventory(unit,unitInventory) end) end
end
 
dfhack.onStateChange.itemsyndrome=function(code)
    if code==SC_WORLD_LOADED then
        itemSyndromeMatIDs = findItemSyndromeInorganic()
        if itemSyndromeMatIDs then itemSyndromeMats = getAllItemSyndromeMats(itemSyndromeMatIDs) end
    end
end
 
if disable then
    eventful.onInventoryChange.itemsyndrome=nil
    print("Disabled itemsyndrome.")
    disable = false
else
    print("Enabled itemsyndrome.")
end

Huzzah! I've updated SWP with this version. (I'm assuming equip-on-transform happening by default was causing some discomfort somewhere?)

Many thanks,

~T