Lua API: Add a valid key to the plugin context and info tables

Previously the only way to tell they were valid would be a protected call on an existing member.

src/scripting/application_lua_kernel.cpp

@@ -110,7 +110,7 @@ application_lua_kernel::application_lua_kernel()
 	cmd_log_ << lua_preferences::register_table(mState);
 }
 
-application_lua_kernel::thread::thread(lua_State * T) : T_(T), started_(false) {}
+application_lua_kernel::thread::thread(application_lua_kernel& owner, lua_State * T) : owner_(owner), T_(T), started_(false) {}
 
 std::string application_lua_kernel::thread::status()
 {
@@ -194,7 +194,7 @@ application_lua_kernel::thread * application_lua_kernel::load_script_from_string
 		throw game::lua_error(std::string("Error when executing a script to make a lua thread -- function was not produced, found a ") + lua_typename(T, lua_type(T, -1)) );
 	}
 
-	return new application_lua_kernel::thread(T);
+	return new application_lua_kernel::thread(*this, T);
 }
 
 application_lua_kernel::thread * application_lua_kernel::load_script_from_file(const std::string & file)
@@ -211,7 +211,7 @@ application_lua_kernel::thread * application_lua_kernel::load_script_from_file(c
 		throw game::lua_error(std::string("Error when executing a file to make a lua thread -- function was not produced, found a ") + lua_typename(T, lua_type(T, -1)) );
 	}
 
-	return new application_lua_kernel::thread(T);
+	return new application_lua_kernel::thread(*this, T);
 }
 
 struct lua_context_backend {
@@ -273,6 +273,9 @@ application_lua_kernel::request_list application_lua_kernel::thread::run_script(
 	// Now we have to create the context object. It is arranged as a table of boost functions.
 	auto this_context_backend = std::make_shared<lua_context_backend>();
 	lua_newtable(T_); // this will be the context table
+	lua_pushstring(T_, "valid");
+	lua_pushboolean(T_, true);
+	lua_settable(T_, -3);
 	for (const std::string & key : ctxt.callbacks_ | boost::adaptors::map_keys ) {
 		lua_pushstring(T_, key.c_str());
 		lua_cpp::push_function(T_, std::bind(&impl_context_backend, std::placeholders::_1, this_context_backend, key));
@@ -284,6 +287,9 @@ application_lua_kernel::request_list application_lua_kernel::thread::run_script(
 	lua_pushstring(T_, "name");
 	lua_pushstring(T_, ctxt.name_.c_str());
 	lua_settable(T_, -3);
+	lua_pushstring(T_, "valid");
+	lua_pushboolean(T_, true);
+	lua_settable(T_, -3);
 	for (const plugins_context::accessor_list::value_type & v : ctxt.accessors_) {
 		const std::string & key = v.first;
 		const plugins_context::accessor_function & func = v.second;
@@ -292,7 +298,14 @@ application_lua_kernel::request_list application_lua_kernel::thread::run_script(
 		lua_settable(T_, -3);
 	}
 
+	// Push copies of the context and info tables so that we can mark them invalid for the next slice
+	lua_pushvalue(T_, -2);
+	lua_pushvalue(T_, -2);
+	// However, Lua can't handle having extra values on the stack when resuming a coroutine,
+	// so move the extra copy to the main thread instead.
+	lua_xmove(T_, owner_.get_state(), 2);
 	// Now we resume the function, calling the coroutine with the three arguments (events, context, info).
+	// We ignore any values returned via arguments to yield()
 	int numres = 0;
 	lua_resume(T_, nullptr, 3, &numres);
 
@@ -324,6 +337,17 @@ application_lua_kernel::request_list application_lua_kernel::thread::run_script(
 		}
 	}
 
+	// Pop any values that the resume left on the stack
+	lua_pop(T_, numres);
+	// Set "valid" to false on the now-expired context and info tables
+	lua_pushstring(owner_.get_state(), "valid");
+	lua_pushboolean(owner_.get_state(), false);
+	lua_settable(owner_.get_state(), -3);
+	lua_pushstring(owner_.get_state(), "valid");
+	lua_pushboolean(owner_.get_state(), false);
+	lua_settable(owner_.get_state(), -4);
+	lua_pop(owner_.get_state(), 2);
+
 	application_lua_kernel::request_list results;
 
 	for (const plugins_manager::event & req : this_context_backend->requests) {

src/scripting/application_lua_kernel.hpp

@@ -33,13 +33,14 @@ public:
 	typedef std::vector<std::function<bool(void)>> request_list;
 
 	class thread {
+		application_lua_kernel& owner_;
 		lua_State * T_;
 		bool started_;
 
 		thread(const thread&) = delete;
 		thread& operator=(const thread&) = delete;
 
-		thread(lua_State *);
+		thread(application_lua_kernel&, lua_State *);
 	public :
 		bool is_running();
 		std::string status();