Include builtin conditions in wesnoth.wml_conditions

This excludes the [true] and [false] ConditionalWML tags,
which are still hard-coded. (People shouldn't be trying to
override or extend these anyway.)

changelog

@@ -31,6 +31,9 @@ Version 1.13.5+dev:
      modifications of the chosen type from a unit. The most efficient use is to
      remove all modifications with a specific duration value.
      Also callable as u:remove_modifications.
+   * The built-in conditionals have_unit, have_location, and variable are now
+     present in the wesnoth.wml_conditionals table. This means they can be directly
+     called, extended with new features, or even overridden with custom implementations.
 * Performance:
    * When a heuristic determines that it's probably faster, the game predicts battle
      outcome by simulating a few thousand fights instead of calculating exact

src/game_events/conditional_wml.cpp

@@ -43,7 +43,7 @@ static lg::log_domain log_engine("engine");
 // This file is in the game_events namespace.
 namespace game_events {
 
-namespace { // Support functions
+namespace builtin_conditions {
 	std::vector<std::pair<int,int> > default_counts = utils::parse_ranges("1-99999");
 
 	bool have_unit(const vconfig& cfg)
@@ -143,7 +143,9 @@ namespace { // Support functions
 #undef TEST_BOL_ATTR
 		return true;
 	}
+}
 
+namespace { // Support functions
 	bool internal_conditional_passed(const vconfig& cond)
 	{
 		if(cond.has_child("true")) {
@@ -160,13 +162,7 @@ namespace { // Support functions
 		for(vconfig::all_children_iterator it = cond.ordered_begin(); it != cond_end; ++it) {
 			std::string key = it.get_key();
 			bool result = true;
-			if(key == "have_unit") {
-				result = have_unit(it.get_child());
-			} else if(key == "have_location") {
-				result = have_location(it.get_child());
-			} else if(key == "variable") {
-				result = variable_matches(it.get_child());
-			} else if(std::find(skip.begin(), skip.end(), key) == skip.end()) {
+			if(std::find(skip.begin(), skip.end(), key) == skip.end()) {
 				assert(resources::lua_kernel);
 				result = resources::lua_kernel->run_wml_conditional(key, it.get_child());
 			}

src/game_events/conditional_wml.hpp

@@ -29,6 +29,12 @@ namespace game_events
 {
 	bool conditional_passed(const vconfig& cond);
 	bool matches_special_filter(const config &cfg, const vconfig& filter);
+
+	namespace builtin_conditions {
+		bool have_unit(const vconfig& cfg);
+		bool have_location(const vconfig& cfg);
+		bool variable_matches(const vconfig& cfg);
+	}
 }
 
 #endif // GAME_EVENTS_CONDITIONAL_WML_H_INCLUDED

src/scripting/game_lua_kernel.cpp

@@ -4895,6 +4895,9 @@ game_lua_kernel::game_lua_kernel(CVideo * video, game_state & gs, play_controlle
 	lua_newtable(L);
 	lua_setfield(L, -2, "wml_conditionals");
 	lua_pop(L, 1);
+	set_wml_condition("have_unit", &game_events::builtin_conditions::have_unit);
+	set_wml_condition("have_location", &game_events::builtin_conditions::have_location);
+	set_wml_condition("variable", &game_events::builtin_conditions::variable_matches);
 
 	// Create the effects table.
 	cmd_log_ << "Adding effects table...\n";
@@ -5225,6 +5228,38 @@ void game_lua_kernel::set_wml_action(std::string const &cmd, game_events::wml_ac
 	lua_pop(L, 2);
 }
 
+using wml_conditional_handler = bool(*)(const vconfig&);
+
+/**
+ * Executes its upvalue as a wml condition and returns the result.
+ */
+static int cfun_wml_condition(lua_State *L)
+{
+	wml_conditional_handler h = reinterpret_cast<wml_conditional_handler>
+		(lua_touserdata(L, lua_upvalueindex(1)));
+
+	vconfig vcfg = luaW_checkvconfig(L, 1);
+	lua_pushboolean(L, h(vcfg));
+	return 1;
+}
+
+/**
+ * Registers a function for use as a conditional handler.
+ */
+void game_lua_kernel::set_wml_condition(std::string const &cmd, wml_conditional_handler h)
+{
+	lua_State *L = mState;
+
+	lua_getglobal(L, "wesnoth");
+	lua_pushstring(L, "wml_conditionals");
+	lua_rawget(L, -2);
+	lua_pushstring(L, cmd.c_str());
+	lua_pushlightuserdata(L, reinterpret_cast<void *>(h));
+	lua_pushcclosure(L, &cfun_wml_condition, 1);
+	lua_rawset(L, -3);
+	lua_pop(L, 2);
+}
+
 /**
  * Runs a command from an event handler.
  * @return true if there is a handler for the command.

src/scripting/game_lua_kernel.hpp

@@ -201,6 +201,7 @@ public:
 	bool run_event(game_events::queued_event const &);
 	void push_builtin_effect();
 	void set_wml_action(std::string const &, game_events::wml_action::handler);
+	void set_wml_condition(std::string const &, bool(*)(const vconfig&));
 	bool run_wml_action(std::string const &, vconfig const &,
 		game_events::queued_event const &);
 	bool run_filter(char const *name, unit const &u);