Allowing plugins to be used as dependencies to other plugins (#16)

* fuck everything i did blegh

* better exception tracking for plugins

* Update PluginLoadContext.Load to return existing instances (basically, make plugin api references possible)

* Update docs to help with plugin dependencies

---------

Co-authored-by: UniPM <zoc6x8voc@mozmail.com>

Minecraft.Server.FourKit/PluginLoadContext.cs

@@ -21,6 +21,13 @@ internal sealed class PluginLoadContext : AssemblyLoadContext
         if (assemblyName.Name == typeof(ServerPlugin).Assembly.GetName().Name)
             return typeof(ServerPlugin).Assembly;
 
+        foreach (var alc in AssemblyLoadContext.All)
+        {
+            var existing = alc.Assemblies
+                .FirstOrDefault(a => a.GetName().Name == assemblyName.Name);
+            if (existing != null) return existing;
+        }
+
         string? path = _resolver.ResolveAssemblyToPath(assemblyName);
         if (path != null)
             return LoadFromAssemblyPath(path);

Minecraft.Server.FourKit/PluginLoader.cs

@@ -81,7 +81,13 @@ internal sealed class PluginLoader
         var assembly = context.LoadFromAssemblyPath(Path.GetFullPath(dllPath));
 
         int found = 0;
-        foreach (var type in assembly.GetTypes())
+        Type[] types;
+        try {
+            types = assembly.GetTypes();
+        } catch (ReflectionTypeLoadException ex) {
+            types = ex.Types.Where(t => t != null).ToArray()!;
+        }
+        foreach (var type in types)
         {
             if (type.IsAbstract || type.IsInterface)
                 continue;
@@ -173,9 +179,10 @@ internal sealed class PluginLoader
         MethodInfo? method = type.GetMethod(camelName, DeclaredPublic, Type.EmptyTypes)
                           ?? type.GetMethod(pascalName, DeclaredPublic, Type.EmptyTypes);
 
-        if (method != null)
-        {
-            method.Invoke(plugin, null);
+        try {
+            method?.Invoke(plugin, null);
+        } catch (TargetInvocationException ex) {
+            throw ex.InnerException ?? ex;
         }
     }
 

Minecraft.Server.FourKit/docs/plugin-creation.md

@@ -264,6 +264,79 @@ When a plugin folder is made, make sure the main dll matches the name of the fol
 
 You can also avoid this by using [Fody Costura](https://github.com/Fody/Costura) and bundle the dependencies into your DLL.
 
+### Plugin Dependencies
+
+In certain cases, like if you wanted to implement an addon to an already existing plugin, you can put the plugin in your .csproj and use functions from that plugin!
+
+This is much like the Dependencies section above, but you shouldn't use Fody Costura for this.
+
+Example of implementing external plugin functions:
+
+```xml
+<ItemGroup>
+    <Reference Include="CoolPlugin">
+        <HintPath>.\CoolPlugin\CoolPlugin.dll</HintPath>
+    </Reference>
+</ItemGroup>
+```
+
+```csharp
+public class PluginAddon : ServerPlugin
+{
+    public override void onEnable() {
+        CoolPlugin.CoolPluginAPI.CoolFunction(arg1, arg2, arg3);
+    }
+}
+```
+
+```csharp
+public class CoolPluginAPI
+{
+    // example API function
+    public static void CoolFunction(arg1, arg2, arg3) {
+        Console.WriteLine("This is a cool function!");
+    }
+}
+```
+
+If the API wants to access instance variables (like a list from the main ServerPlugin), you will have to make sure the instance is already initialized.
+
+This is because the plugin referencing the API might load before the actual plugin with the API. The API will be usable, but not the instance.
+
+You can do this by initializing the instance in the API if its not already initialized.
+
+```csharp
+public class CoolPlugin : ServerPlugin
+{
+    private static CoolPlugin? _instance;
+    public static CoolPlugin? getInstance() => _instance;
+    internal static void setInstance(CoolPlugin inst) => _instance = inst;
+
+    // example instance variable
+    internal List<int> coolList = [];
+
+    public override void onEnable() {
+        // initializes the instance if it isn't already initialized
+        instance ??= this;
+    }
+}
+```
+
+```csharp
+public class CoolPluginAPI
+{
+    // guarantee an instance when the API is used
+    internal static CoolPlugin? getCoolPlugin() {
+        if (CoolPlugin.getInstance() == null) CoolPlugin.setInstance(new CoolPlugin());
+        return CoolPlugin.getInstance();
+    }
+
+    public static void CoolFunction(arg1, arg2, arg3) {
+        getCoolPlugin()?.coolList.Add(404);
+    }
+}
+```
+
 ### Fody Costura
 
 Fody Costura isnt very well documented, but heres the general usage guide that has worked for users:
@@ -300,4 +373,4 @@ Fody Costura isnt very well documented, but heres the general usage guide that h
     Build
     <p>After you've done all this, it should build and put all dependencies into one DLL in your output folder.</p>
   </li>
-</ol>
+</ol>