Rudimentary cleanup of falling leaf node issues.

When a leaf node is displaced by crushing by a falling node,
instead of ejecting an item, try to place the node itself within
a reasonable distance.

This shoudl reduce the number of stack nodes generated from tree
canopy decay, and should alleviate the inconsistency of leaves
falling sometimes as nodes and sometimes as stacks.

docs/issues.txt

@@ -9,18 +9,13 @@ ISSUES: Bugs, Cleanup and Refinements
  #    #  #       #    #     #    #       #       #   #   #    #
   ####   #        ####      #    ######  ######  #    #   ####
 
-- Redesign how falling_nodes pile up.
-	- Make sure nodes are not destroyed.
-	- Allow node displacement sideways?
-	- Maybe force column to coordinate settling in order, to
-	  avoid race conditions?
-	- Check for early settling on node of same type, e.g. for
-	  falling leaves.
-
 - First-class support for stack "pez dispensers".
 	- Upon digging a stack node, try to shift all inventories from
 	  stack nodes above downward.
 
+- Sponges grow way too much.
+	- Inhibit growth based on total neighbors.
+
 - Hint system updates.
 	- Need a "witness" system for spontaneous in-world processes,
 	  such as tree growth or lode cooling.  Credit players within

mods/nc_items/ent_falling.lua

@@ -1,10 +1,29 @@
 -- LUALOCALS < ---------------------------------------------------------
-local ItemStack, minetest, setmetatable
-    = ItemStack, minetest, setmetatable
+local ItemStack, math, minetest, nodecore, pairs, setmetatable, unpack
+    = ItemStack, math, minetest, nodecore, pairs, setmetatable, unpack
+local math_random
+    = math.random
 -- LUALOCALS > ---------------------------------------------------------
 
 local modname = minetest.get_current_modname()
 
+local function readd(oldadd, pos, item, ...)
+	local stack = ItemStack(item)
+	item = stack:get_name()
+	if stack:get_count() ~= 1 or (not
+		minetest.registered_nodes[item]) then
+		return oldadd(pos, item, ...)
+	end
+	pos = nodecore.scan_flood(pos, 5,
+		function(p)
+			if p.y > pos.y and math_random() < 0.95 then return end
+			if p.y > pos.y + 1 then return end
+			if nodecore.buildable_to(p) then return p end
+		end)
+	if not pos then return oldadd(pos, item, ...) end
+	minetest.set_node(pos, {name = item})
+end
+
 local bifn = minetest.registered_entities["__builtin:falling_node"]
 local falling = {
 	set_node = function(self, node, meta, ...)
@@ -18,6 +37,26 @@ local falling = {
 			end
 		end
 		return bifn.set_node(self, node, meta, ...)
+	end,
+	on_step = function(...)
+		local oldadd = minetest.add_item
+		local drops = {}
+		minetest.add_item = function(pos, item, ...)
+			drops[#drops + 1] = {pos, item, ...}
+		end
+		local oldnode = minetest.add_node
+		minetest.add_node = function(pos, node, ...)
+			oldnode(pos, node, ...)
+			for _, v in pairs(drops) do
+				readd(oldadd, unpack(v))
+			end
+			drops = {}
+		end
+		local function helper(...)
+			minetest.add_item = oldadd
+			return ...
+		end
+		return helper(bifn.on_step(...))
 	end
 }
 setmetatable(falling, bifn)