Add support for extension private deps

src/Core/ExtensionsManager.cs

@@ -4,6 +4,7 @@
 using SwarmUI.Utils;
 using System.IO;
 using System.Reflection;
+using System.Runtime.Loader;
 
 namespace SwarmUI.Core;
 
@@ -15,11 +16,40 @@ public class ExtensionsManager
     /// <summary>Hashset of folder names of all extensions currently loaded.</summary>
     public HashSet<string> LoadedExtensionFolders = [];
 
+    /// <summary>Hashset of dependency names that are considered "core" and should not be loaded from the extension's folder.</summary>
+    public HashSet<string> CoreDependencyNames = [];
+
     /// <summary>Simple holder of information about extensions available online.</summary>
     public record class ExtensionInfo(string Name, string Author, string License, string Description, string URL, string OldURL, string[] Tags, string[] FolderNames)
     {
     }
 
+    private class SwarmExtensionLoadContext(ExtensionsManager manager, string name, string extensionDir) : AssemblyLoadContext(name, isCollectible: false)
+    {
+        /// <summary>Host wins, then we probe the extension's folder for private deps.</summary>
+        protected override Assembly Load(AssemblyName name)
+        {
+            string dependency = Path.Combine(extensionDir, name.Name + ".dll");
+            try
+            {
+                Default.LoadFromAssemblyName(name);
+                // We only get here if host successfully loads the assembly.
+                if (File.Exists(dependency) && !manager.CoreDependencyNames.Contains(name.Name))
+                {
+                    Logs.Warning($"Extension {Name} ships {name.Name}.dll but host already has it loaded; using host copy.");
+                }
+                return null;
+            }
+            catch (FileNotFoundException) { }
+            if (!File.Exists(dependency))
+            {
+                return null;
+            }
+            Logs.Debug($"Extension {Name} loading private dep {name.Name} from {dependency}");
+            return LoadFromAssemblyPath(dependency);
+        }
+    }
+
     public static HtmlString HtmlTags(string[] tags)
     {
         return new(tags.Select(t =>
@@ -45,6 +75,11 @@ public static HtmlString HtmlTags(string[] tags)
     /// <summary>List of known online available extensions.</summary>
     public List<ExtensionInfo> KnownExtensions = [];
 
+    private Assembly LoadInExtensionContext(string dllName, string targetPath)
+    {
+        return new SwarmExtensionLoadContext(this, dllName, Path.GetDirectoryName(targetPath)).LoadFromAssemblyPath(targetPath);
+    }
+
     public static string ReferenceCsproj =
         """
         <Project Sdk="Microsoft.NET.Sdk.Web">
@@ -58,6 +93,11 @@ public static HtmlString HtmlTags(string[] tags)
     /// <summary>Initial call that prepares the extensions list.</summary>
     public async Task PrepExtensions()
     {
+        CoreDependencyNames =
+        [
+            .. AssemblyLoadContext.Default.Assemblies.Select(a => a.GetName().Name).Where(n => n is not null),
+            .. Directory.EnumerateFiles(AppContext.BaseDirectory, "*.dll").Select(Path.GetFileNameWithoutExtension)
+        ];
         await BuildPublicExtensionList();
         string[] builtins = [.. Directory.EnumerateDirectories("./src/BuiltinExtensions").Select(s => "src/" + s.Replace('\\', '/').AfterLast("/src/"))];
         string[] extras = Directory.Exists("./src/Extensions") ? [.. Directory.EnumerateDirectories("./src/Extensions/").Select(s => "src/" + s.Replace('\\', '/').AfterLast("/src/"))] : [];
@@ -181,7 +221,7 @@ public async Task<Assembly> BuildExtension(string folder, string projFile)
         if (File.Exists(target) && !Program.IsDevMode)
         {
             Logs.Debug($"Don't need to rebuild extension {projFile}, already built.");
-            return Assembly.LoadFile(Path.GetFullPath(target));
+            return LoadInExtensionContext(dllName, Path.GetFullPath(target));
         }
         Logs.Debug($"Building extension project: {projFile}...");
         string buildParam = $"-p:BaseIntermediateOutputPath={Path.GetFullPath($"./src/obj/extensions/{dllName}/")};TargetName={dllName}-{hash}";
@@ -195,7 +235,7 @@ public async Task<Assembly> BuildExtension(string folder, string projFile)
         {
             Logs.Debug($"Successful build output for extension project {projFile}:\n{output}");
         }
-        return Assembly.LoadFile(Path.GetFullPath(target));
+        return LoadInExtensionContext(dllName, Path.GetFullPath(target));
     }
 
     public void PrepExtension(Type extType, bool isCore, string[] possible)