Document changed API and restore backwards compatibility

27e216112e changed the API of mcl_armor.register_set to facilitate
automated localization string extraction. This wasn't documented and mods
depending on the old contract were broken.

This also fixes translation of leather armor that was partially depending
on the old API contract.

mods/ITEMS/mcl_armor/API.md

@@ -13,6 +13,18 @@ mcl_armor.register_set({
 	--name of the armor material (used for generating itemstrings)
 	name = "dummy_armor",
 
+	--localized description of each armor piece
+	descriptions = {
+		head = S("Dummy Cap"),
+		torso = S("Dummy Tunic"),
+		legs = S("Dummy Pants"),
+		feet = S("Dummy Shoes"),
+	},
+
+	--The following MCL2 compatible legacy behavior is still supported, but
+	--deprecated, because it interferes with proper localization
+	--it is triggered when description is non nil
+	--[[
 	--description of the armor material
 	--do NOT translate this string, it will be concatenated will each piece of armor's description and result will be automatically fetched from your mod's translation files
 	description = "Dummy Armor",
@@ -25,6 +37,7 @@ mcl_armor.register_set({
 		legs = "Pants",  --default: "Leggings"
 		feet = "Shoes",  --default: "Boots"
 	},
+	]]
 
 	--this is used to calculate each armor piece durability with the minecraft algorithm
 	--head durability = durability * 0.6857 + 1

mods/ITEMS/mcl_armor/api.lua

@@ -119,6 +119,16 @@ function mcl_armor.register_set(def)
 	local durabilities = def.durabilities or {}
 	local element_groups = def.element_groups or {}
 
+	-- backwards compatibility
+	local descriptions = def.descriptions or {}
+	if def.description then
+		minetest.log("warning", "[mcl_armor] using the description field of armor set definitions is deprecated, please provide the localized strings in def.descriptions instead. Currently processing " .. def.name)
+		local S = minetest.get_translator(modname)
+		for name, element in pairs(mcl_armor.elements) do
+			descriptions[name] = S(def.description .. " " .. (descriptions[name] or element.description))
+		end
+	end
+
 	for name, element in pairs(mcl_armor.elements) do
 		local itemname = element.name .. "_" .. def.name
 		local itemstring = modname .. ":" .. itemname
@@ -143,7 +153,7 @@ function mcl_armor.register_set(def)
 		end
 
 		minetest.register_tool(itemstring, {
-			description = def.descriptions[name],
+			description = descriptions[name],
 			_doc_items_longdesc = mcl_armor.longdesc,
 			_doc_items_usagehelp = mcl_armor.usage,
 			inventory_image = modname .. "_inv_" .. itemname .. ".png",

mods/ITEMS/mcl_armor/init.lua

@@ -6,6 +6,7 @@ mcl_armor = {
 	elements = {
 		head = {
 			name = "helmet",
+			description = "Helmet", -- provided for backwards compatability
 			durability = 0.6857,
 			index = 2,
 			craft = function(m)
@@ -18,6 +19,7 @@ mcl_armor = {
 		},
 		torso = {
 			name = "chestplate",
+			description = "Chestplate", -- provided for backwards compatability
 			durability = 1.0,
 			index = 3,
 			craft = function(m)
@@ -30,6 +32,7 @@ mcl_armor = {
 		},
 		legs = {
 			name = "leggings",
+			description = "Leggings", -- provided for backwards compatability
 			durability = 0.9375,
 			index = 4,
 			craft = function(m)
@@ -42,6 +45,7 @@ mcl_armor = {
 		},
 		feet = {
 			name = "boots",
+			description = "Boots", -- provided for backwards compatability
 			durability = 0.8125,
 			index = 5,
 			craft = function(m)