No default values for trees, leaves and range in treecapitator.register_tree

These default tree definition options are non-obvious,
so although their use may slightly shorten code in a few situations,
the code would be more difficult to understand.

To check for backwards-compatibility problems,
`treecapitator.register_tree` now checks if these three options are set when required.
Furthermore, `treecapitator.register_tree` now no longer modifies the passed table in-place.

This is a breaking change since there might exist mod which uses the default values.

api.lua

@@ -1,15 +1,37 @@
 -- the table containing the tree definitions
 treecapitator.trees = {}
 
+-- Warn if a tree definition passed to treecapitator.register_tree contains
+-- invalid options, partly for backwards compatibility.
+-- Not all options are checked.
+local function check_tree_definition(tr)
+	if type(tr.trees) ~= "table" then
+		minetest.log("warning",
+			"[treecapitator] Invalid tree definition (trees field)")
+	end
+	if tr.type ~= "acacia" then
+		if type(tr.leaves) ~= "table" then
+			minetest.log("warning",
+				"[treecapitator] Invalid tree definition (leaves field)")
+		end
+		if type(tr.range) ~= "number" then
+			minetest.log("warning",
+				"[treecapitator] Invalid tree definition (range field)")
+		end
+	end
+end
+
 -- For the usage of this function, see trees.lua.
 local after_dig_wrap
 local after_dig_nodes = {}
-function treecapitator.register_tree(tr)
-	for name,value in pairs(treecapitator.default_tree) do
-		if tr[name] == nil then
-			tr[name] = value	--replaces not defined stuff
-		end
+function treecapitator.register_tree(tree_definition)
+	check_tree_definition(tree_definition)
+	local tr = {}
+	for name, value in pairs(tree_definition) do
+		tr[name] = value
 	end
+	tr.fruits = tr.fruits or {}
+	tr.type = tr.type or "default"
 	treecapitator.trees[#treecapitator.trees+1] = tr
 	if treecapitator.after_register[tr.type] then
 		treecapitator.after_register[tr.type](tr)

init.lua

@@ -12,13 +12,6 @@ treecapitator = {
 	no_hand_capitation = false,
 	delay = 0,
 	stem_height_min = 3,
-	default_tree = {	--replaces not defined stuff (see below)
-		trees = {"default:tree"},
-		leaves = {"default:leaves"},
-		range = 2,
-		fruits = {},
-		type = "default",
-	},
 	after_register = {},
 }