run_command: implement support for async functions.

Also update //for to make use of this new functionality.

//subdivide is still on the todo list.

The new functionality works by adding the new property `async = false` to command definition tables registered via wea_core.register_command()`. When `true`, if and only if the command's MAIN FUNC ONLY returns no values at all then it will consider an async operation to be in progress.

This delays `run_command` from emitting the `post-execute` event on `wea_core`.

Additionally, all async commands have a callback function injected as the first argument to their main `func` (ref main cmd definition table). This callback function -- if no arguments are returned by the main `func` -- must be called once the async operation is complete with same args you would normally return from `func` -- that is `success, result_message`. These will then be handled as normal and sent to the player as appropriate, as well as finally emitting the `post-execute` event.

BUG: There is a potential issue in this implementation, in that if i.e. `minetest.after()` is used to delay async execution then this will break out of the `xpcall()` protection in place to prevent crashes. To this end, if you implement an async function you need to be very careful, and do a manual `wea_core.safe_function()` call yourself!

worldeditadditions_commands/commands/meta/for.lua

@@ -15,7 +15,7 @@ local wea_c = worldeditadditions_core
 -- ?Basename support for values
 -- ?Comma deliniation support for values
 
-local function step(params)
+local function step(params, __callback)
 	-- Initialize additional params on first call
 	if not params.first then
 		params.i = 1 -- Iteration number
@@ -37,12 +37,9 @@ local function step(params)
 	
 	if params.i <= #params.values then
 		-- If we haven't run out of values call function again
-		minetest.after(0, step, params)
+		minetest.after(0, step, params, __callback)
 	else
-		wea_c.notify.ok(params.player_name, "For "..
-			table.concat(params.values,", ")..
-			", /"..params.cmd_name.." completed in " ..
-			wea_c.format.human_time(params.time))
+		__callback(true, "//for completed mapping values ["..table.concat(params.values, ", ").."] over /"..params.cmd_name.." "..tostring(params.args).." in "..wea_c.format.human_time(params.time))
 	end
 end
 
@@ -50,6 +47,7 @@ worldeditadditions_core.register_command("for", {
 	params = "<value1> <value2> <value3>... do //<command> <arg> %% <arg>",
 	description = "Executes a chat command for each value before \" do \" replacing any instances of \"%%\" with those values. The forward slashes at the beginning of the chat command must be the same as if you were executing it normally.",
 	privs = { worldedit = true },
+	async = true,
 	parse = function(params_text)
 		if not params_text:match("%sdo%s") then
 			return false, "Error: \"do\" argument is not present."
@@ -68,7 +66,9 @@ worldeditadditions_core.register_command("for", {
 		
 		return true, values, command, args
 	end,
-	func = function(name, values, command, args)
+	func = function(__callback, name, values, command, args)
+		print("DEBUG://for __callback", wea_c.inspect(__callback), "name", name)
+		
 		local cmd = minetest.registered_chatcommands[command]
 		if not cmd then
 			return false, "Error: "..command.." isn't a valid command."
@@ -77,13 +77,17 @@ worldeditadditions_core.register_command("for", {
 			return false, "Your privileges are insufficient to run /\""..command.."\"."
 		end
 		
+		
 		step({
 			player_name = name,
 			cmd_name = command,
 			values = values,
 			cmd = cmd,
 			args = args
-		})
+		}, __callback)
 		
+		-- Returning nothing + async = true means we're going async and we'll get back to `run_command` later. Until then, I'm going to have to put you on hold :P
+		-- * cue hold music *
+		-- ref https://youtu.be/3to4vaWl2dY
 	end
 })

worldeditadditions_core/core/register_command.lua

@@ -15,12 +15,20 @@ end
 
 
 --- Registers a new WorldEditAdditions chat command.
+-- 
+-- **Async commands:** Set `async = true` in the definition table you pass to this function. THEN, to indicate you are doing an async thing return NO VALUES AT ALL from your main `func` that is passed the parsed arguments. When `async = true`, your main `func` will be passed a callback function as the 1st argument BEFORE all other arguments.
+--
+-- Call this function when you are done with all async work with the same variables you would return: success: bool, result_message: string.
+--
+-- **IMPORTANT:** You MUST NOT return `success, result_message` from the main function AND call the callback function in a single call of a command!
+-- An example of this in action can be seen in the implementation of `//for`.
 -- @param	cmdname		string	The name of the command to register.
 -- @param	options		table	A table of options for the command:
 -- - `params` (string) A textual description of the parameters the command takes.
 -- - `description` (string) A description of the command.
 -- - `privs` (`{someprivilege=true, ....}`) The privileges required to use the command.
 -- - `require_pos` (number) The number of positions required for the command.
+-- - `async=false` (bool) Whether this function is async. See the note in the description of this function for more information.
 -- - `parse` (function) A function that parses the raw param_text into proper input arguments to be passed to `nodes_needed` and `func`.
 -- - `nodes_needed` (function) A function that returns the number of nodes the command could potential change given the parsed input arguments.
 -- - `func` (function) The function to execute when the command is run.
@@ -56,6 +64,7 @@ local function register_command(cmdname, options)
 	---
 	-- 2: Normalisation
 	---
+	if options.async == nil then options.async = false end
 	if not options.privs then options.privs = {} end
 	if not options.require_pos then options.require_pos = 0 end
 	if not options.nodes_needed then options.nodes_needed = function() return 0 end end

worldeditadditions_core/core/run_command.lua

@@ -7,6 +7,26 @@ local safe_region = dofile(weac.modpath.."/core/safe_region.lua")
 local human_size = weac.format.human_size
 local safe_function = weac.safe_function
 
+--- Handles the success bool and result message string that a command's main `func` returns.
+-- @param success	bool	Whether the command executed successfully or not.
+-- @param result_message	string	The message (as a string) to send to the player.
+local function handle_success_resultmsg(player_name, cmdname, success, result_message)
+	if success then
+		if not result_message then
+			result_message = "//" .. tostring(cmdname) .. " successful"
+		end
+		weac.notify.ok(player_name, result_message)
+	else
+		if not result_message then
+			result_message =
+			"An unspecified (likely user) error was returned by the command. It is a bug that a specific error message is not returned here. It is not necessarily a bug that an error was thrown: your command invocation could have contained invalid syntax, for example."
+		end
+		weac.notify.error(player_name, "[//" .. tostring(cmdname) .. "] " .. result_message)
+	end
+	
+	return success, result_message
+end
+
 --- Actually runs the command in question. [HIDDEN]
 -- Unfortunately needed to keep the codebase clena because Lua sucks.
 -- @internal
@@ -17,29 +37,52 @@ local safe_function = weac.safe_function
 -- @returns	nil
 local function run_command_stage2(player_name, func, parse_result, tbl_event)
 	weac:emit("pre-execute", tbl_event)
-	local success_safefn, retvals = safe_function(func, { player_name, weac.table.unpack(parse_result) }, player_name, "The function crashed during execution.", tbl_event.cmdname)
+	
+	-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~#
+	
+	local args = {}
+	-- If we're async, add the callback function as the 1st argument before everything else
+	if tbl_event.cmddef.async then
+		table.insert(args, function(success, result_message)
+			success, result_message = handle_success_resultmsg(player_name, tbl_event.cmdname, success, result_message)
+			
+			tbl_event.success = success
+			tbl_event.result = result_message
+			weac:emit("post-execute", tbl_event)
+		end)
+	end
+	-- Add player_name, unpack(args_from_parse_func).... afterwards 
+	table.insert(args, player_name)
+	for _,value in ipairs(parse_result) do
+		table.insert(args, value)
+	end
+	
+	-- Run the cmd itself and catch errors
+	local success_safefn, retvals = safe_function(func, args, player_name, "The function crashed during execution.", tbl_event.cmdname)
 	if not success_safefn then return false end
 	
-	if #retvals ~= 2 then
-		weac.notify.error(player_name, "[//"..tostring(tbl_event.cmdname).."] The main execution function for this chat command returned "..tostring(#retvals).." arguments instead of the expected 2 (success, message), so it is unclear whether it succeeded or not. This is a bug!")
+	-- BELOW: We handle the IMMEDIATE RETURN VALUE. For async commands this requires special handling as the actual exit of async commands is above.
+	
+	-- If a function is async (pass `async = true` in the table passed to weac.register_command()`), then if there are no return values then we assume it was successful.
+	if #retvals ~= 2 and not tbl_event.cmddef.async then
+		weac.notify.error(player_name, "[//"..tostring(tbl_event.cmdname).."] This command is not async and the main execution function for it returned "..tostring(#retvals).." arguments instead of the expected 2 (success, message), so it is unclear whether it succeeded or not. This is a bug!")
+	end
+	 
+	if #retvals == 2 then
+		local success, result_message = retvals[1], retvals[2]
+		success, result_message = handle_success_resultmsg(player_name, tbl_event.cmdname, success, result_message)
+		
+		tbl_event.success = success
+		tbl_event.result = result_message
+		
 	end
 	
-	local success, result_message = retvals[1], retvals[2]
-	print("DEBUG:run_command_stage2 SUCCESS", success, "RESULT_MESSAGE", result_message)
-	if success then
-		if not result_message then
-			result_message = "//"..tostring(tbl_event.cmdname).." successful"
-		end
-		weac.notify.ok(player_name, result_message)
-	else
-		if not result_messasge then
-			result_message = "An unspecified (likely user) error was returned by the command. It is a bug that a specific error message is not returned here. It is not necessarily a bug that an error was thrown: your command invocation could have contained invalid syntax, for example."
-		end
-		weac.notify.error(player_name, "[//"..tostring(tbl_event.cmdname).."] "..result_message)
+	-- This is outside the above before we need to fire post-execute even if `#retvals ~= 2` or something else happened
+	-- 
+	-- Don't fire the post-execute event if async = true unless we were explicitly told its fine. If async = false then just go right ahead anyway
+	if not tbl_event.cmddef.async or (tbl_event.cmddef.async and success) then
+		weac:emit("post-execute", tbl_event)
 	end
-	tbl_event.success = success
-	tbl_event.result = result_message
-	weac:emit("post-execute", tbl_event)
 end
 
 
@@ -93,7 +136,8 @@ end
 -- - `paramargs` (table): The parsed arguments returned by the parsing function. Available in `post-parse` and later.
 -- - `potential_changes` (number): The number of potential nodes that could be changed as a result of running the command. `post-nodesneeded` and later: remember not all commands have an associated `nodesneeded` function.
 -- - `success` (boolean): Whether the command executed successfully or not. Available only in `post-execute`.
--- - `result` (any): The `result` value returned by the command function. Value depends on the command executed. Available only in `post-execute`.
+-- - `result` (any): The `result` value returned by the command function. Value depends on the command executed. Available only in `post-execute`. SHOULD be a string but don't count on it.
+-- 
 -- @param	cmdname		string	The name of the command to run.
 -- @param	options		table	The table of options associated with the command. See worldeditadditions_core.register_command for more information.
 -- @param	player_name	string	The name of the player to execute the command for.