Fixed some Version Handler issues in 2019.3+

If VersionHandler.UpdateNow() is called from a static
constructor in Unity 2019.3 (which is TBH undefined behavior)
Unity does not save asset metadata changes to disk leaving
all newly _enabled_ plugins in a disabled state.

This changes all entry points to UpdateVersionedAssets() to
run the core logic on the editor thread if possible so that
metadata changes are correctly applied when the asset database
is refreshed.

Other minor clean ups:
- Moved log level loading into a shared method that is used
  by all public entry points.
- Changed calls to UpdateVersionedAssets() from the
  AssetPostProcessor method to excecute after 2s so that
  batch asset changes don't result in multiple calls to
  UpdateVersionedAssets().
- Improved logging of loaded manifests.
- Minor speed up of loaded assembly polling.

Change-Id: I0effaa84c21a13ac5c615520a1a2eb1751d071c5

Author: Stewart Miles

source/VersionHandlerImpl/src/VersionHandlerImpl.cs

@@ -1774,10 +1774,17 @@ public bool ParseManifests(FileMetadataByVersion metadataByVersion,
             var obsoleteFilesSorted = new List<string>(obsoleteFiles);
             currentFilesSorted.Sort();
             obsoleteFilesSorted.Sort();
-            Log(String.Format("'{0}' Manifest:\n\nCurrent files:\n{1}\n\nObsolete files:\n{2}",
-                              filenameCanonical,
-                              String.Join("\n", currentFilesSorted.ToArray()),
-                              String.Join("\n", obsoleteFilesSorted.ToArray())),
+            var components = new List<string>();
+            if (currentFilesSorted.Count > 0) {
+                components.Add(String.Format("Current files:\n{0}",
+                                             String.Join("\n", currentFilesSorted.ToArray())));
+            }
+            if (obsoleteFilesSorted.Count > 0) {
+                components.Add(String.Format("Obsolete files:\n{0}",
+                                             String.Join("\n", obsoleteFilesSorted.ToArray())));
+            }
+            Log(String.Format("'{0}' Manifest:\n{1}",
+                              filenameCanonical, String.Join("\n", components.ToArray())),
                 verbose: true);
             return true;
         }
@@ -2148,6 +2155,13 @@ public static Logger Logger {
         InstallSourceFilename = Assembly.GetAssembly(typeof(VersionHandlerImpl)).Location
     };
 
+    /// <summary>
+    /// Load log preferences.
+    /// </summary>
+    private static void LoadLogPreferences() {
+        VerboseLoggingEnabled = VerboseLoggingEnabled;
+    }
+
     /// <summary>
     /// Enables / disables assets imported at multiple revisions / versions.
     /// In addition, this module will read text files matching _manifest_
@@ -2156,8 +2170,7 @@ public static Logger Logger {
     static VersionHandlerImpl() {
         Log("Loaded VersionHandlerImpl", verbose: true);
         RunOnMainThread.Run(() => {
-                // Load log preferences.
-                VerboseLoggingEnabled = VerboseLoggingEnabled;
+                LoadLogPreferences();
                 UpdateVersionedAssetsOnUpdate();
             }, runNow: false);
     }
@@ -2196,7 +2209,10 @@ private static bool EnabledEditorDllsLoaded {
             var loadedAssemblyPaths = new HashSet<string>();
             foreach (var assembly in AppDomain.CurrentDomain.GetAssemblies()) {
                 try {
-                    loadedAssemblyPaths.Add(Path.GetFullPath(assembly.Location));
+                    var path = Path.GetFullPath(assembly.Location);
+                    if (enabledEditorDlls.Contains(path)) {
+                        loadedAssemblyPaths.Add(path);
+                    }
                 } catch (NotSupportedException) {
                     // Dynamic assemblies do not have a file location so ignore.
                 }
@@ -2432,6 +2448,7 @@ public static void ShowSettings() {
     /// </summary>
     [MenuItem("Assets/External Dependency Manager/Version Handler/Update")]
     public static void UpdateNow() {
+        LoadLogPreferences();
         UpdateVersionedAssets(true, () => {
                 Dialog.Display(PLUGIN_NAME, "Update complete.", 0, "OK");
             });
@@ -2589,6 +2606,20 @@ public static void UpdateVersionedAssets(bool forceUpdate) {
     /// <param name="forceUpdate">Whether to force an update.</param>
     /// <param name="complete">Called when this is method is complete.</param>
     public static void UpdateVersionedAssets(bool forceUpdate, Action complete) {
+        CancelUpdateVersionedAssets();
+        RunOnMainThread.Run(() => { UpdateVersionedAssetsOnMainThread(forceUpdate, complete); },
+                            runNow: false);
+    }
+
+    /// <summary>
+    /// Find all files in the asset database with multiple version numbers
+    /// encoded in their filename, select the most recent revisions and
+    /// delete obsolete versions and files referenced by old manifests that
+    /// are not present in the most recent manifests.
+    /// </summary>
+    /// <param name="forceUpdate">Whether to force an update.</param>
+    /// <param name="complete">Called when this is method is complete.</param>
+    private static void UpdateVersionedAssetsOnMainThread(bool forceUpdate, Action complete) {
         // If this module is disabled do nothing.
         if (!forceUpdate && !Enabled) {
             complete();
@@ -2784,14 +2815,35 @@ public static float GetUnityVersionMajorMinor() {
         return ExecutionEnvironment.VersionMajorMinor;
     }
 
+    // ID of the scheduled job which performs an update.
+    private static int updateVersionedAssetsJob = 0;
+
+    /// <summary>
+    /// Cancel the update versioned assets job.
+    /// </summary>
+    private static void CancelUpdateVersionedAssets() {
+        if (updateVersionedAssetsJob > 0) {
+            RunOnMainThread.Cancel(updateVersionedAssetsJob);
+            updateVersionedAssetsJob = 0;
+        }
+    }
+
     /// <summary>
     /// Scanned for versioned assets and apply modifications if required.
     /// </summary>
     private static void OnPostprocessAllAssets(
             string[] importedAssets, string[] deletedAssets,
             string[] movedAssets, string[] movedFromPath) {
         ManifestReferences.FlushCaches();
-        UpdateVersionedAssets();
+        if (Enabled) {
+            const double UpdateDelayInMiliseconds = 2000;
+            CancelUpdateVersionedAssets();
+            updateVersionedAssetsJob =
+                RunOnMainThread.Schedule(() => {
+                        UpdateVersionedAssets();
+                    },
+                    UpdateDelayInMiliseconds);
+        }
     }
 
     /// <summary>