Initial commit

LoaderGuard.cs

@@ -0,0 +1,45 @@
+// SPDX-License-Identifier: GPL-3.0-only
+using System;
+using System.Collections.Generic;
+using System.Reflection;
+using System.Runtime.InteropServices;
+
+namespace BlockMelonLoader
+{
+    public static class LoaderGuard
+    {
+        public static void EnsureAllowed(string modName)
+        {
+            EnsureAllowed(modName, AppDomain.CurrentDomain.GetAssemblies(), ShowAlert, Environment.FailFast);
+        }
+
+        internal static void EnsureAllowed(string modName, IEnumerable<Assembly> assemblies,
+            Action<string> showAlert, Action<string> terminate)
+        {
+            foreach (var assembly in assemblies)
+            {
+                if (!string.Equals(assembly.GetName().Name, "MelonLoader", StringComparison.OrdinalIgnoreCase))
+                    continue;
+
+                var message = modName + " cannot run while MelonLoader is active.\n\n"
+                    + "Remove MelonLoader and install this mod using Unity Mod Manager.\n\n"
+                    + "The game will close after this message.";
+                // Loader exception handlers can swallow a thrown exception, so termination
+                // must happen even if the native dialog fails.
+                try { showAlert(message); }
+                finally { terminate(message); }
+                return;
+            }
+        }
+
+        private static void ShowAlert(string message)
+        {
+            Console.Error.WriteLine(message);
+            if (Environment.OSVersion.Platform == PlatformID.Win32NT)
+                MessageBoxW(IntPtr.Zero, message, "Unsupported mod loader", 0x10 | 0x10000);
+        }
+
+        [DllImport("user32.dll", CharSet = CharSet.Unicode, ExactSpelling = true)]
+        private static extern int MessageBoxW(IntPtr window, string text, string caption, uint type);
+    }
+}