Implement safe require

builtin/init.lua

@@ -49,6 +49,72 @@ dofile(commonpath .. "serialize.lua")
 dofile(commonpath .. "misc_helpers.lua")
 
 if INIT == "game" then
+	local function mod_loader(module_name)
+		local parts = module_name:split(".")
+		local modname = parts[1]
+		local modpath = core.get_modpath(modname)
+		if not modpath then
+			return "no mod called " .. modname
+		end
+		parts[1] = modpath
+		local base_path = table.concat(parts, "/")
+		local errors = {}
+		for _, suffix in ipairs({"/init.lua", #parts > 1 and ".lua" or nil}) do
+			local source_path = base_path .. suffix
+			local f, err = io.open(source_path, "r")
+			if f then
+				local source = f:read("*all")
+				local chunk, load_err = loadstring(source, source_path)
+				f:close()
+				assert(chunk, load_err)
+				return chunk
+			else
+				table.insert(errors, err)
+			end
+		end
+		return table.concat(errors, "\n")
+	end
+
+	local function preprocess_module_name(module_name)
+		if module_name:sub(1, 1) == "." then
+			module_name = assert(core.get_current_modname()) .. module_name
+		end
+		assert(module_name:find("^[A-Za-z0-9_%.]+$") and
+				module_name:find("%.%.") == nil and
+				module_name:sub(-1) ~= ".",
+				"invalid module name")
+		return module_name
+	end
+
+	local loaded = {} -- [module_name] = function() return module end
+	package = {
+		loaders = {mod_loader},
+		unload = function(module_name)
+			loaded[preprocess_module_name(module_name)] = nil
+		end,
+		set = function(module_name, module)
+			loaded[preprocess_module_name(module_name)] = function() return module end
+		end,
+	}
+	function require(module_name)
+		module_name = preprocess_module_name(module_name)
+		local module_func = loaded[module_name]
+		if module_func then
+			return module_func()
+		end
+		local errors = {}
+		for _, loader in ipairs(package.loaders) do
+			local res = loader(module_name)
+			if type(res) == "function" then
+				local module = res()
+				package.set(module_name, module)
+				return module
+			end
+			table.insert(errors, res)
+		end
+		error("failed to load module '" .. module_name .. '":\n' .. table.concat(errors, "\n"))
+	end
+
 	dofile(scriptdir .. "game" .. DIR_DELIM .. "init.lua")
 	assert(not core.get_http_api)
 elseif INIT == "mainmenu" then

doc/lua_api.md

@@ -4121,6 +4121,36 @@ For example:
 * `core.dir_to_wallmounted` (Involves wallmounted param2 values.)
 
 
+Loading files
+=============
+
+The typical way to load files until 5.13.0 was to use `dofile`
+and run files in order of dependencies in `init.lua`, e.g.
+
+```lua
+local modname = core.get_current_modname()
+local modpath = core.get_modpath(modname)
+dofile(modname .. "/stuff.lua")
+dofile(modname .. "/more_stuff.lua")
+```
+
+This is clunky and has several drawbacks.
+As of version 5.13.0, Luanti supports a custom version of Lua's `require`:
+
+* `require("mymod")` gives you whatever `init.lua` of `mymod` returns.
+  You should have a dependency (optional or not) on `mymod` if you call this.
+* `require("mod.dir.file")` loads `dir/file.lua` or `dir/file/init.lua` from the mod folder of `mod`.
+* For convenience, `require(".dir.file")` is equivalent to `require(core.get_current_modname() .. ".dir.file")`.
+  This is also supported by the `package.*` functions.
+
+The implementation is customizable via the `package` table:
+
+* `package.loaders` is a list of loaders which are tried in order.
+  A loader is a `function(module_name)` which returns `nil`,
+  a string explaining why it couldn't load the module,
+  or a function that when called returns the module.
+* `package.unload(module_name)` can be used to forcibly unload a module.
+* `package.set(module_name, module)` can be used to override a module.
 
 
 Helper functions

games/devtest/.luacheckrc

@@ -33,6 +33,7 @@ read_globals = {
 	string = {fields = {"split", "trim"}},
 	table = {fields = {"copy", "getn", "indexof", "insert_all", "key_value_swap"}},
 	math = {fields = {"hypot", "round"}},
+	package = {fields = {"loaders", "unload", "set"}}
 }
 
 globals = {

games/devtest/mods/unittests/init.lua

@@ -246,3 +246,9 @@ else
 		end,
 	})
 end
+
+local t = {}
+unittests.register("test_mod_require", function()
+	assert(require("unittests") == t)
+end)
+return t

games/devtest/mods/unittests/misc.lua

@@ -353,3 +353,27 @@ local function test_ipc_poll(cb)
 	print("delta: " .. (core.get_us_time() - t0) .. "us")
 end
 unittests.register("test_ipc_poll", test_ipc_poll)
+
+do
+	local t = require(".require")
+	assert(t.foo == "bar")
+	assert(t == require("unittests.require"))
+	package.unload(".require")
+	assert(t ~= require(".require"))
+	package.set(".require", "test")
+	assert(require(".require") == "test")
+end
+
+do
+	local status, err = xpcall(function()
+		table.insert(package.loaders, function()
+			return function()
+				return 42
+			end
+		end)
+		local answer = require("the_answer_to_life_the_universe_and_all_the_rest")
+		assert(answer == 42)
+	end, debug.traceback)
+	table.remove(package.loaders)
+	assert(status, err)
+end

games/devtest/mods/unittests/require.lua

@@ -0,0 +1 @@
+return {foo = "bar"}

src/script/cpp_api/s_base.cpp

@@ -13,6 +13,7 @@
 #include "porting.h"
 #include "util/string.h"
 #include "server.h"
+#include <lua.h>
 #if CHECK_CLIENT_BUILD()
 #include "client/client.h"
 #endif
@@ -229,38 +230,53 @@ std::string ScriptApiBase::getCurrentModNameInsecure(lua_State *L)
 	return ret;
 }
 
-void ScriptApiBase::loadMod(const std::string &script_path,
-		const std::string &mod_name)
-{
-	ModNameStorer mod_name_storer(getStack(), mod_name);
-
-	loadScript(script_path);
-}
-
-void ScriptApiBase::loadScript(const std::string &script_path)
+static void load_script(lua_State *L, const char *script_path, int nresults)
 {
 	verbosestream << "Loading and running script from " << script_path << std::endl;
 
-	lua_State *L = getStack();
-
 	int error_handler = PUSH_ERROR_HANDLER(L);
 
 	bool ok;
 	if (ScriptApiSecurity::isSecure(L)) {
-		ok = ScriptApiSecurity::safeLoadFile(L, script_path.c_str());
+		ok = ScriptApiSecurity::safeLoadFile(L, script_path);
 	} else {
-		ok = !luaL_loadfile(L, script_path.c_str());
+		ok = !luaL_loadfile(L, script_path);
 	}
-	ok = ok && !lua_pcall(L, 0, 0, error_handler);
+	ok = ok && !lua_pcall(L, 0, nresults, error_handler);
 	if (!ok) {
 		const char *error_msg = lua_tostring(L, -1);
 		if (!error_msg)
 			error_msg = "(error object is not a string)";
 		lua_pop(L, 2); // Pop error message and error handler
-		throw ModError("Failed to load and run script from " +
+		throw ModError(std::string("Failed to load and run script from ") +
 				script_path + ":\n" + error_msg);
 	}
-	lua_pop(L, 1); // Pop error handler
+	lua_remove(L, error_handler);
+	// leave the return values from loading the file on the stack
+}
+
+void ScriptApiBase::loadMod(const std::string &script_path,
+		const std::string &mod_name, bool package_set)
+{
+	lua_State *L = getStack();
+	int top = lua_gettop(L);
+	ModNameStorer mod_name_storer(L, mod_name);
+
+	load_script(L, script_path.c_str(), 1);
+	if (package_set) {
+		int module = lua_gettop(L);
+		lua_getglobal(L, "package");
+		lua_getfield(L, -1, "set");
+		lua_pushstring(L, mod_name.c_str());
+		lua_pushvalue(L, module);
+		lua_call(L, 2, 0);
+	}
+	lua_settop(L, top);
+}
+
+void ScriptApiBase::loadScript(const std::string &script_path)
+{
+	load_script(getStack(), script_path.c_str(), 0);
 }
 
 #if CHECK_CLIENT_BUILD()

src/script/cpp_api/s_base.h

@@ -73,7 +73,8 @@ public:
 	DISABLE_CLASS_COPY(ScriptApiBase);
 
 	// These throw a ModError on failure
-	void loadMod(const std::string &script_path, const std::string &mod_name);
+	void loadMod(const std::string &script_path, const std::string &mod_name,
+			bool package_set = false);
 	void loadScript(const std::string &script_path);
 
 #if CHECK_CLIENT_BUILD()

src/server/mods.cpp

@@ -44,7 +44,7 @@ void ServerModManager::loadMods(ServerScripting &script)
 
 		auto t1 = porting::getTimeMs();
 		std::string script_path = mod.path + DIR_DELIM + "init.lua";
-		script.loadMod(script_path, mod.name);
+		script.loadMod(script_path, mod.name, true);
 		infostream << "Mod \"" << mod.name << "\" loaded after "
 			<< (porting::getTimeMs() - t1) << " ms" << std::endl;
 	}