Forbid renaming of written books

GROUPS.md

@@ -52,6 +52,7 @@ Please read <http://minecraft.gamepedia.com/Breaking> to learn how digging times
 * `can_eat_when_full=1`: Only for foodstuffs. This item can be eaten when the user has a full hunger bar
 * `attached_node_facedir=1`: Like `attached_node`, but for facedir nodes
 * `cauldron`: Cauldron. 1: Empty. 2-4: Water height
+* `no_rename=1`: Item cannot be renamed by anvil
 
 #### Footnotes
 

mods/ITEMS/mcl_anvils/init.lua

@@ -38,6 +38,10 @@ local function update_anvil_slots(meta)
 			else
 				name_item = input1
 			end
+			-- No renaming allowed with group no_rename=1
+			if minetest.get_item_group(name_item:get_name(), "no_rename") == 1 then
+				new_output = ""
+			else
 				local meta = name_item:get_meta()
 				-- Limit name length
 				new_name = string.sub(new_name, 1, 30)
@@ -46,6 +50,7 @@ local function update_anvil_slots(meta)
 				-- Double-save the name internally, too
 				meta:set_string("name", new_name)
 				new_output = name_item
+			end
 		else
 			new_output = ""
 		end

mods/ITEMS/mcl_books/init.lua

@@ -179,7 +179,7 @@ minetest.register_craftitem("mcl_books:written_book", {
 
 To copy the text of the written book, place it into the crafting grid together with a book and quill (or multiple of those) and craft. The written book will not be consumed. Copies of copies can not be copied.]],
 	inventory_image = "mcl_books_book_written.png",
-	groups = { not_in_creative_inventory=1, book=1 },
+	groups = { not_in_creative_inventory=1, book=1, no_rename=1 },
 	stack_max = 16,
 	on_place = read,
 	on_secondary_use = read