start working on assembly loader

to be used with the generated assemblies from the user code.

Nerfed.Editor/Project/EditorAssemblyLoadContext.cs

@@ -0,0 +1,8 @@
+using System.Runtime.Loader;
+
+namespace Nerfed.Editor.Project;
+
+internal class EditorAssemblyLoadContext : AssemblyLoadContext
+{
+    public EditorAssemblyLoadContext() : base(isCollectible: true) { }
+}

Nerfed.Editor/Project/EditorAssemblyLoader.cs

@@ -0,0 +1,109 @@
+using Nerfed.Runtime;
+using System.Diagnostics;
+using System.Reflection;
+using System.Runtime.CompilerServices;
+
+namespace Nerfed.Editor.Project;
+
+// https://github.com/godotengine/godot/blob/master/modules/mono/glue/GodotSharp/GodotPlugins/Main.c
+// https://gitlab.com/robertk92/assemblyreloadtest/-/blob/main/AppContextTest/Program.cs
+
+internal static class EditorAssemblyLoader
+{
+    private sealed class EditorAssemblyLoadContextWrapper
+    {
+        private EditorAssemblyLoadContext assemblyLoadContext;
+        private readonly WeakReference weakReference;
+
+        private EditorAssemblyLoadContextWrapper(EditorAssemblyLoadContext assemblyLoadContext, WeakReference weakReference)
+        {
+            this.assemblyLoadContext = assemblyLoadContext;
+            this.weakReference = weakReference;
+        }
+
+        public bool IsCollectible
+        {
+            [MethodImpl(MethodImplOptions.NoInlining)]
+            // If assemblyLoadContext is null we already started unloading, so it was collectible.
+            get => assemblyLoadContext?.IsCollectible ?? true;
+        }
+
+        public bool IsAlive
+        {
+            [MethodImpl(MethodImplOptions.NoInlining)]
+            get => weakReference.IsAlive;
+        }
+
+        [MethodImpl(MethodImplOptions.NoInlining)]
+        public static (Assembly, EditorAssemblyLoadContextWrapper) CreateAndLoad(AssemblyName assemblyName)
+        {
+            EditorAssemblyLoadContext context = new EditorAssemblyLoadContext();
+            WeakReference reference = new WeakReference(context, trackResurrection: true);
+            EditorAssemblyLoadContextWrapper wrapper = new EditorAssemblyLoadContextWrapper(context, reference);
+            Assembly assembly = context.LoadFromAssemblyName(assemblyName);
+            return (assembly, wrapper);
+        }
+
+        [MethodImpl(MethodImplOptions.NoInlining)]
+        internal void Unload()
+        {
+            assemblyLoadContext?.Unload();
+            assemblyLoadContext = null;
+        }
+    }
+
+    private static (Assembly, EditorAssemblyLoadContextWrapper) Load(string assemblyFilePath)
+    {
+        string assemblyFileName = Path.GetFileNameWithoutExtension(assemblyFilePath);
+
+        AssemblyName assemblyName = new AssemblyName(assemblyFileName);
+
+        return EditorAssemblyLoadContextWrapper.CreateAndLoad(assemblyName);
+    }
+
+    private static bool Unload(EditorAssemblyLoadContextWrapper assemblyLoadContextWrapper)
+    {
+        if (assemblyLoadContextWrapper == null)
+        {
+            return true;
+        }
+
+        if (!assemblyLoadContextWrapper.IsCollectible) 
+        {
+            Log.Error($"{assemblyLoadContextWrapper} is not collectable!");
+            return false;
+        }
+
+        assemblyLoadContextWrapper.Unload();
+
+        GC.Collect();
+        GC.WaitForPendingFinalizers();
+
+        TimeSpan timeout = TimeSpan.FromSeconds(30);
+        Stopwatch stopwatch = Stopwatch.StartNew();
+
+        while (assemblyLoadContextWrapper.IsAlive) 
+        {
+            GC.Collect(GC.MaxGeneration, GCCollectionMode.Forced);
+            GC.WaitForPendingFinalizers();
+
+            if (!assemblyLoadContextWrapper.IsAlive)
+            {
+                break;
+            }
+
+            if (stopwatch.Elapsed.TotalSeconds % 10 == 0)
+            {
+                Log.Info("Tring to unload assembly...");
+            }
+
+            if (stopwatch.Elapsed >= timeout)
+            {
+                Log.Error("Failed to unload assembly!");
+                return false;
+            }
+        }
+
+        return true;
+    }
+}