Add plugin hot reload

Flow.Launcher.Core/Plugin/IResultUpdateRegister.cs

@@ -9,4 +9,10 @@ public interface IResultUpdateRegister
     /// </summary>
     /// <param name="pair"></param>
     void RegisterResultsUpdatedEvent(PluginPair pair);
+
+    /// <summary>
+    /// Unregister a plugin from the results updated event, e.g. before the plugin is unloaded or reloaded.
+    /// </summary>
+    /// <param name="pair"></param>
+    void UnregisterResultsUpdatedEvent(PluginPair pair);
 }

Flow.Launcher.Core/Plugin/PluginAssemblyLoader.cs

@@ -2,7 +2,9 @@
 using System.IO;
 using System.Linq;
 using System.Reflection;
+using System.Runtime.CompilerServices;
 using System.Runtime.Loader;
+using System.Threading.Tasks;
 
 namespace Flow.Launcher.Core.Plugin
 {
@@ -13,11 +15,43 @@ internal class PluginAssemblyLoader : AssemblyLoadContext
         private readonly AssemblyName assemblyName;
 
         internal PluginAssemblyLoader(string assemblyFilePath)
+            : base(name: Path.GetFileNameWithoutExtension(assemblyFilePath), isCollectible: true)
         {
             dependencyResolver = new AssemblyDependencyResolver(assemblyFilePath);
             assemblyName = new AssemblyName(Path.GetFileNameWithoutExtension(assemblyFilePath));
         }
 
+        /// <summary>
+        /// Initiates unload of the given load context and returns a weak reference that can be used to
+        /// verify the context has actually been collected. Kept in a separate non-inlined method so the
+        /// caller's stack frame holds no strong reference to the context that would prevent collection.
+        /// </summary>
+        [MethodImpl(MethodImplOptions.NoInlining)]
+        internal static WeakReference UnloadAndGetWeakReference(PluginAssemblyLoader loader)
+        {
+            var weakReference = new WeakReference(loader);
+            loader.Unload();
+            return weakReference;
+        }
+
+        /// <summary>
+        /// Waits for an unloaded context to be collected. Returns false if the context is still alive
+        /// after all attempts, which means something (e.g. a cached delegate) is pinning the old assembly.
+        /// </summary>
+        internal static async Task<bool> WaitForUnloadAsync(WeakReference weakReference, int maxAttempts = 10)
+        {
+            for (var i = 0; i < maxAttempts && weakReference.IsAlive; i++)
+            {
+                GC.Collect();
+                GC.WaitForPendingFinalizers();
+                if (!weakReference.IsAlive) return true;
+                // ConfigureAwait(false) keeps the blocking GC loop off the UI thread's context
+                await Task.Delay(100).ConfigureAwait(false);
+            }
+
+            return !weakReference.IsAlive;
+        }
+
         internal Assembly LoadAssemblyAndDependencies()
         {
             return LoadFromAssemblyName(assemblyName);

Flow.Launcher.Core/Plugin/PluginConfig.cs

@@ -110,7 +110,7 @@ internal static (List<PluginMetadata>, List<PluginMetadata>) GetUniqueLatestPlug
             return (unique_list, duplicate_list);
         }
 
-        private static PluginMetadata GetPluginMetadata(string pluginDirectory)
+        internal static PluginMetadata GetPluginMetadata(string pluginDirectory)
         {
             string configPath = Path.Combine(pluginDirectory, Constant.PluginMetadataFileName);
             if (!File.Exists(configPath))

Flow.Launcher.Core/Plugin/PluginInstaller.cs

@@ -91,7 +91,13 @@ await DownloadFileAsync(
             return; // do not restart on failure
         }
 
-        if (Settings.AutoRestartAfterChanging)
+        if (Settings.HotReloadAfterChanging && await PluginManager.ReloadPluginAsync(newPlugin.ID))
+        {
+            PublicApi.Instance.ShowMsg(
+                Localize.installbtn(),
+                Localize.InstallSuccessHotReload(newPlugin.Name));
+        }
+        else if (Settings.AutoRestartAfterChanging)
         {
             PublicApi.Instance.RestartApp();
         }
@@ -186,7 +192,14 @@ public static async Task UninstallPluginAndCheckRestartAsync(PluginMetadata oldP
             return; // don not restart on failure
         }
 
-        if (Settings.AutoRestartAfterChanging)
+        if (Settings.HotReloadAfterChanging && !PublicApi.Instance.PluginModified(oldPlugin.ID))
+        {
+            // The plugin was fully unloaded and its directory deleted, so no restart is needed
+            PublicApi.Instance.ShowMsg(
+                Localize.uninstallbtn(),
+                Localize.UninstallSuccessHotReload(oldPlugin.Name));
+        }
+        else if (Settings.AutoRestartAfterChanging)
         {
             PublicApi.Instance.RestartApp();
         }
@@ -246,7 +259,13 @@ await DownloadFileAsync(
             return; // do not restart on failure
         }
 
-        if (Settings.AutoRestartAfterChanging)
+        if (Settings.HotReloadAfterChanging && await PluginManager.ReloadPluginAsync(oldPlugin.ID))
+        {
+            PublicApi.Instance.ShowMsg(
+                Localize.updatebtn(),
+                Localize.UpdateSuccessHotReload(newPlugin.Name));
+        }
+        else if (Settings.AutoRestartAfterChanging)
         {
             PublicApi.Instance.RestartApp();
         }
@@ -328,6 +347,7 @@ where string.Compare(existingPlugin.Metadata.Version, pluginUpdateSource.Version
     public static async Task UpdateAllPluginsAsync(IEnumerable<PluginUpdateInfo> resultsForUpdate, bool restart)
     {
         var anyPluginSuccess = false;
+        var allPluginsHotReloaded = true;
         await Task.WhenAll(resultsForUpdate.Select(async plugin =>
         {
             var downloadToFilePath = Path.Combine(Path.GetTempPath(), $"{plugin.Name}-{plugin.NewVersion}.zip");
@@ -343,26 +363,40 @@ await DownloadFileAsync(
                 // check if user cancelled download before installing plugin
                 if (cts.IsCancellationRequested)
                 {
+                    allPluginsHotReloaded = false;
                     return;
                 }
 
                 if (!await PublicApi.Instance.UpdatePluginAsync(plugin.PluginExistingMetadata, plugin.PluginNewUserPlugin, downloadToFilePath))
                 {
+                    allPluginsHotReloaded = false;
                     return;
                 }
 
                 anyPluginSuccess = true;
+
+                if (!Settings.HotReloadAfterChanging || !await PluginManager.ReloadPluginAsync(plugin.ID))
+                {
+                    allPluginsHotReloaded = false;
+                }
             }
             catch (Exception e)
             {
+                allPluginsHotReloaded = false;
                 PublicApi.Instance.LogException(ClassName, "Failed to update plugin", e);
                 PublicApi.Instance.ShowMsgError(Localize.ErrorUpdatingPlugin());
             }
         }));
 
         if (!anyPluginSuccess) return;
 
-        if (restart)
+        if (allPluginsHotReloaded)
+        {
+            PublicApi.Instance.ShowMsg(
+                Localize.updatebtn(),
+                Localize.PluginsUpdateSuccessHotReload());
+        }
+        else if (restart)
         {
             PublicApi.Instance.RestartApp();
         }