Added [lua] conditional tag

Also made conditions fail if they encountered a syntax or runtime error. This seems the
more logical behavior than passing.

WML conditional tags were split into their own Lua file. The one in lua/wml/object.lua
relies on local variables so was left there.

changelog

@@ -64,6 +64,8 @@ Version 1.13.10+dev:
    * [show_if] is now usable in [objectives] subtag [gold_carryover].
    * Macro SCEPTRE_OF_FIRE_EFFECT damage increased to 15x4 so Sceptre is an
      improvement over the uncut ruby of fire (14x4) in TRoW.
+   * Added [lua] as a conditional tag.
+   * Lua errors now cause as a condition to fail instead of pass.
  * Miscellaneous and bug fixes:
    * Fixed crash after canceling add-on download (bug #2203)
    * Fixed ingame help showing units you haven't encountered (bug #2135)
@@ -71,7 +73,7 @@ Version 1.13.10+dev:
      greater (bug #2185).
    * Fix recalls updating shroud immediately when "Delay Shroud Updates" is set
      (bug #2196)
-   * Fixed not being able to undo previous moves after entering planning mode 
+   * Fixed not being able to undo previous moves after entering planning mode
      (bug #2303)
 
 Version 1.13.10:

data/lua/wml-conditionals.lua

@@ -0,0 +1,22 @@
+local helper = wesnoth.require "helper"
+
+function wesnoth.wml_conditionals.proceed_to_next_scenario(cfg)
+	local endlevel_data = wesnoth.get_end_level_data()
+
+	if not endlevel_data then
+		return false
+	else
+		return endlevel_data.proceed_to_next_level
+	end
+end
+
+function wesnoth.wml_conditionals.lua(cfg)
+	cfg = helper.shallow_literal(cfg)
+	local bytecode, message = load(cfg.code or "")
+
+	if not bytecode then
+		error("~lua:" .. message, 0)
+	else
+		return bytecode(helper.get_child(cfg, "args"))
+	end
+end

data/lua/wml-tags.lua

@@ -15,6 +15,7 @@ function wesnoth.game_events.on_save()
 	return {}
 end
 
+wesnoth.require "wml-conditionals"
 wesnoth.require "wml-flow"
 wesnoth.require "wml"
 
@@ -939,15 +940,6 @@ function wesnoth.wml_actions.story(cfg)
 	wesnoth.show_story(cfg, title)
 end
 
-function wesnoth.wml_conditionals.proceed_to_next_scenario(cfg)
-	local endlevel_data = wesnoth.get_end_level_data()
-	if not endlevel_data then
-		return false
-	else
-		return endlevel_data.proceed_to_next_level
-	end
-end
-
 function wesnoth.wml_actions.cancel_action(cfg)
 	wesnoth.cancel_action()
 end

src/scripting/game_lua_kernel.cpp

@@ -4502,25 +4502,31 @@ bool game_lua_kernel::run_wml_action(const std::string& cmd, vconfig const &cfg,
 
 
 /**
- * Runs a command from an event handler.
- * @return true if there is a handler for the command.
- * @note @a cfg should be either volatile or long-lived since the Lua
- *       code may grab it for an arbitrary long time.
+ * Evaluates a WML conidition.
+ *
+ * @returns Whether the condition passed.
+ * @note    @a cfg should be either volatile or long-lived since the Lua
+ *          code may grab it for an arbitrarily long time.
  */
-bool game_lua_kernel::run_wml_conditional(const std::string& cmd, vconfig const &cfg)
+bool game_lua_kernel::run_wml_conditional(const std::string& cmd, const vconfig& cfg)
 {
-	lua_State *L = mState;
+	lua_State* L = mState;
 
-
-	if (!luaW_getglobal(L, "wesnoth", "wml_conditionals", cmd)) {
+	// If an invalid coniditional tag is used, consider it a pass.
+	if(!luaW_getglobal(L, "wesnoth", "wml_conditionals", cmd)) {
 		lg::wml_error() << "unknown conditional wml: [" << cmd << "]\n";
 		return true;
 	}
 
 	luaW_pushvconfig(L, cfg);
-	luaW_pcall(L, 1, 1, true);
+
+	// Any runtime error is considered a fail.
+	if(!luaW_pcall(L, 1, 1, true)) {
+		return false;
+	}
 
 	bool b = luaW_toboolean(L, -1);
+
 	lua_pop(L, 1);
 	return b;
 }