Ensure FileMetadata does not attempt to update UPM files.

FileMetadata synchronizes asset labels with properties on the
class which does not work with UPM as UPM will restore the files
after modification, cause an asset database refresh which then
causes FileMetadata to synchronize asset labels and so on.

This adds the IsReadOnly property to FileMetadata to determine
whether it references a file that should not be modified. This
property is used to prevent modification of asset metadata by
the class. In addition, this is used to simplify FileMetadataSet
filtering.

Bug: 150902136
Change-Id: I570456e463f694adada53f039f01f3a5265568df

Author: Stewart Miles

source/VersionHandlerImpl/src/VersionHandlerImpl.cs

@@ -352,6 +352,17 @@ public string ManifestName {
             }
         }
 
+        /// <summary>
+        /// Whether it's possible to change the asset metadata.
+        /// </summary>
+        /// <returns>true if the asset metadata for this file is read-only,
+        /// false otherwise.</return>
+        public bool IsReadOnly {
+            get {
+                return FileUtils.IsUnderDirectory(filename, FileUtils.PACKAGES_FOLDER);
+            }
+        }
+
         /// <summary>
         /// Parse metadata from filename and store in this class.
         /// </summary>
@@ -646,7 +657,9 @@ public HashSet<string> GetDotNetTargets() {
         /// Save metadata from this class into the asset's labels.
         /// </summary>
         public void UpdateAssetLabels() {
-            if (String.IsNullOrEmpty(AssetDatabase.AssetPathToGUID(filename))) return;
+            if (String.IsNullOrEmpty(AssetDatabase.AssetPathToGUID(filename)) || IsReadOnly) {
+                return;
+            }
             AssetImporter importer = AssetImporter.GetAtPath(filename);
             var labels = new List<string>();
             var currentLabels = new List<string>();
@@ -1168,19 +1181,15 @@ public Dictionary<string, FileMetadata> MetadataByFilename {
         public FileMetadataSet() { }
 
         /// <summary>
-        /// Filter all files that were installed by the Unity Package Manager.
+        /// Filter all files that can't be modified.
         /// </summary>
         /// <param name="metadataSet">Metadata set to filter.</param>
-        /// <returns>New FileMetadata with Unity Package Manager files removed.</returns>
-        public static FileMetadataSet FilterOutUnityPackageManagerFiles(
-                FileMetadataSet metadataSet) {
+        /// <returns>New FileMetadata with files that can't be modified removed.</returns>
+        public static FileMetadataSet FilterOutReadOnlyFiles(FileMetadataSet metadataSet) {
             var filteredMetadata = new FileMetadataSet();
             foreach (var metadataByVersion in metadataSet.Values) {
                 foreach (var metadata in metadataByVersion.Values) {
-                    if (!FileUtils.IsUnderDirectory(metadata.filename,
-                                                    FileUtils.PACKAGES_FOLDER)) {
-                        filteredMetadata.Add(metadata);
-                    }
+                    if (!metadata.IsReadOnly) filteredMetadata.Add(metadata);
                 }
             }
             return filteredMetadata;
@@ -1744,7 +1753,7 @@ public static List<ManifestReferences> FindAndReadManifests() {
         /// </summary>
         /// <returns>List of ManifestReferences from Assets folder</returns>
         public static List<ManifestReferences> FindAndReadManifestsInAssetsFolder() {
-            return FindAndReadManifests(FileMetadataSet.FilterOutUnityPackageManagerFiles(
+            return FindAndReadManifests(FileMetadataSet.FilterOutReadOnlyFiles(
                 FileMetadataSet.ParseFromFilenames(FindAllAssets())));
         }
 
@@ -2468,7 +2477,7 @@ public static void UpdateVersionedAssets(bool forceUpdate, Action complete) {
 
         UpdateAssetsWithBuildTargets(EditorUserBuildSettings.activeBuildTarget);
 
-        var metadataSet = FileMetadataSet.FilterOutUnityPackageManagerFiles(
+        var metadataSet = FileMetadataSet.FilterOutReadOnlyFiles(
             FileMetadataSet.ParseFromFilenames(FindAllAssets()));
         // Rename linux libraries, if any are being tracked.
         var linuxLibraries = new LinuxLibraryRenamer(metadataSet);