static SortedDictionary <string, bool> GetHandledExtensionsByImporter(ScriptedImporterAttribute attribute)
        {
            var handledExts = new SortedDictionary <string, bool>();

            if (attribute.fileExtensions != null)
            {
                var fileExtensions = attribute.fileExtensions.Distinct(StringComparer.OrdinalIgnoreCase);
                foreach (var fileExtension in fileExtensions)
                {
                    var cleanExt = fileExtension.Trim('.');
                    if (!string.IsNullOrEmpty(cleanExt))
                    {
                        handledExts.Add(cleanExt, true);
                    }
                }
            }

            if (attribute.overrideFileExtensions != null)
            {
                var overrideFileExtensions = attribute.overrideFileExtensions.Distinct(StringComparer.OrdinalIgnoreCase);
                foreach (var fileExtension in overrideFileExtensions)
                {
                    var cleanExt = fileExtension.Trim('.');
                    if (!string.IsNullOrEmpty(cleanExt) && !handledExts.ContainsKey(cleanExt))
                    {
                        handledExts.Add(cleanExt, false);
                    }
                }
            }
            return(handledExts);
        }
        internal static void RegisterScriptedImporters()
        {
            //Find the types with the 'ScriptedImporter' attribute which also derive from 'ScriptedImporter'
            var importers = new List <Type>();

            foreach (var type in TypeCache.GetTypesWithAttribute <ScriptedImporterAttribute>())
            {
                if (type.IsSubclassOf(typeof(ScriptedImporter)))
                {
                    importers.Add(type);
                }
                else
                {
                    Debug.LogError(String.Format("{0} has a 'ScriptedImporter' Attribute but is not a subclass of 'ScriptedImporter'.", type.ToString()));
                }
            }

            ScriptedImporterAttribute[]       scriptedImporterAttributes = new ScriptedImporterAttribute[importers.Count];
            SortedDictionary <string, bool>[] handledExtensions          = new SortedDictionary <string, bool> [importers.Count];

            Dictionary <string, List <int> > importersByExtension = new Dictionary <string, List <int> >();

            // Build a dictionary of which importers are trying to register each extension that we can use to quickly find conflicts
            // (i.e. if an entry in the extension-keyed dictionary has a list of importers with more than one entry)
            for (var importerIndex = 0; importerIndex < importers.Count; importerIndex++)
            {
                Type importer = importers[importerIndex];
                scriptedImporterAttributes[importerIndex] = Attribute.GetCustomAttribute(importer, typeof(ScriptedImporterAttribute)) as ScriptedImporterAttribute;
                handledExtensions[importerIndex]          = GetHandledExtensionsByImporter(scriptedImporterAttributes[importerIndex]);

                if (handledExtensions[importerIndex].Count == 0)
                {
                    Debug.LogError($"The ScriptedImporter {importer.FullName} does not provide any non-null file extension.");
                }

                foreach (KeyValuePair <string, bool> handledExtension in handledExtensions[importerIndex])
                {
                    // Only consider AutoSelected ones
                    if (handledExtension.Value)
                    {
                        // Add this importer to the dictionary entry for this file extension, creating it if not already present
                        if (!importersByExtension.TryGetValue(handledExtension.Key, out List <int> importerIndicesForThisExtension))
                        {
                            importerIndicesForThisExtension = new List <int>();
                            importersByExtension.Add(handledExtension.Key, importerIndicesForThisExtension);
                        }
                        importerIndicesForThisExtension.Add(importerIndex);
                    }
                }
            }

            // Check each AutoSelected extension we found, any of them that have more than one importer associated with them are rejected (i.e. removed from all importers that provided them)
            foreach (KeyValuePair <string, List <int> > importerExtension in importersByExtension)
            {
                if (importerExtension.Value.Count > 1)
                {
                    string rejectedImporters = "";
                    foreach (int importerIndex in importerExtension.Value)
                    {
                        handledExtensions[importerIndex].Remove(importerExtension.Key);

                        if (rejectedImporters.Length != 0)
                        {
                            rejectedImporters = $"{rejectedImporters}, ";
                        }
                        rejectedImporters = $"{rejectedImporters}{importers[importerIndex].FullName} (assembly: {importers[importerIndex].Module.FullyQualifiedName})";
                    }
                    Debug.LogError(String.Format("Multiple scripted importers are targeting the extension '{0}' and have all been rejected: {1} ", importerExtension.Key, rejectedImporters));
                }
            }

            for (var index = 0; index < importers.Count; index++)
            {
                var importer    = importers[index];
                var attribute   = scriptedImporterAttributes[index];
                var handledExts = handledExtensions[index];

                if (handledExts.Count > 0)
                {
                    var supportsImportDependencyHinting =
                        (importer.GetMethod("GetHashOfImportedAssetDependencyHintsForTesting", BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Static) != null) ||
                        IsStaticMethodInClassOrParent(importer, "GatherDependenciesFromSourceFile");

                    // Register the importer
                    foreach (var ext in handledExts)
                    {
                        AssetImporter.RegisterImporter(importer, attribute.version, attribute.importQueuePriority, ext.Key, supportsImportDependencyHinting, ext.Value, attribute.AllowCaching);
                    }
                }
            }
        }