Add: [Script] GSAsyncMode to set async mode of gamescript commands (#10913)

In asynchronous mode, don't wait for result of executed command,
just fire-and-forget, and return estimated cost/result

src/script/api/script_asyncmode.cpp

@@ -0,0 +1,61 @@
+/*
+ * This file is part of OpenTTD.
+ * OpenTTD is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 2.
+ * OpenTTD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ * See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with OpenTTD. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/** @file script_asyncmode.cpp Implementation of ScriptAsyncMode. */
+
+#include "../../stdafx.h"
+#include "script_asyncmode.hpp"
+#include "../script_instance.hpp"
+#include "../script_fatalerror.hpp"
+
+#include "../../safeguards.h"
+
+bool ScriptAsyncMode::AsyncModeProc()
+{
+	/* In async mode we only return 'true', telling the DoCommand it
+	 *  should stop run the command in asynchronous/fire-and-forget mode. */
+	return true;
+}
+
+bool ScriptAsyncMode::NonAsyncModeProc()
+{
+	/* In non-async mode we only return 'false', normal operation. */
+	return false;
+}
+
+ScriptAsyncMode::ScriptAsyncMode(HSQUIRRELVM vm)
+{
+	int nparam = sq_gettop(vm) - 1;
+	if (nparam < 1) {
+		throw sq_throwerror(vm, "You need to pass a boolean to the constructor");
+	}
+
+	SQBool sqasync;
+	if (SQ_FAILED(sq_getbool(vm, 2, &sqasync))) {
+		throw sq_throwerror(vm, "Argument must be a boolean");
+	}
+
+	this->last_mode     = this->GetDoCommandMode();
+	this->last_instance = this->GetDoCommandModeInstance();
+
+	this->SetDoCommandAsyncMode(sqasync ? &ScriptAsyncMode::AsyncModeProc : &ScriptAsyncMode::NonAsyncModeProc, this);
+}
+
+void ScriptAsyncMode::FinalRelease()
+{
+	if (this->GetDoCommandAsyncModeInstance() != this) {
+		/* Ignore this error if the script already died. */
+		if (!ScriptObject::GetActiveInstance()->IsDead()) {
+			throw Script_FatalError("Asyncmode object was removed while it was not the latest *Mode object created.");
+		}
+	}
+}
+
+ScriptAsyncMode::~ScriptAsyncMode()
+{
+	this->SetDoCommandAsyncMode(this->last_mode, this->last_instance);
+}