Improve caching of `FilesystemFilterSet.ToString`

src/BizHawk.Client.Common/FilesystemFilterSet.cs

@@ -9,28 +9,30 @@ namespace BizHawk.Client.Common
 {
 	public sealed class FilesystemFilterSet
 	{
-		private string? _allSer = null;
+		private string? _ser = null;
 
-		public readonly IReadOnlyCollection<FilesystemFilter> Filters;
+		public bool AppendAllFilesEntry { get; init; } = true;
+
+		public string? CombinedEntryDesc { get; init; } = null;
+
+		private IReadOnlyCollection<string> CombinedExts
+			=> Filters.SelectMany(static filter => filter.Extensions).Distinct().Order().ToList();
+
+		public readonly IReadOnlyList<FilesystemFilter> Filters;
 
 		public FilesystemFilterSet(params FilesystemFilter[] filters)
+			=> Filters = filters;
+
+		public override string ToString()
 		{
-			Filters = filters;
-		}
-
-		/// <remarks>appends <c>All Files</c> entry (calls <see cref="ToString(bool)"/> with <see langword="true"/>), return value is a valid <c>Filter</c> for <c>Save-</c>/<c>OpenFileDialog</c></remarks>
-		public override string ToString() => ToString(true);
-
-		/// <remarks>call other overload to prepend combined entry, return value is a valid <c>Filter</c> for <c>Save-</c>/<c>OpenFileDialog</c></remarks>
-		public string ToString(bool addAllFilesEntry) => addAllFilesEntry
-			? $"{ToString(false)}|{FilesystemFilter.AllFilesEntry}"
-			: string.Join("|", Filters.Select(filter => filter.ToString()));
-
-		/// <remarks>call other overload (omit <paramref name="combinedEntryDesc"/>) to not prepend combined entry, return value is a valid <c>Filter</c> for <c>Save-</c>/<c>OpenFileDialog</c></remarks>
-		public string ToString(string combinedEntryDesc, bool addAllFilesEntry = true)
-		{
-			_allSer ??= FilesystemFilter.SerializeEntry(combinedEntryDesc, Filters.SelectMany(static filter => filter.Extensions).Distinct().Order().ToList());
-			return $"{_allSer}|{ToString(addAllFilesEntry)}";
+			if (_ser is null)
+			{
+				var entries = Filters.Select(static filter => filter.ToString()).ToList();
+				if (CombinedEntryDesc is not null) entries.Insert(0, FilesystemFilter.SerializeEntry(CombinedEntryDesc, CombinedExts));
+				if (AppendAllFilesEntry) entries.Add(FilesystemFilter.AllFilesEntry);
+				_ser = string.Join("|", entries);
+			}
+			return _ser;
 		}
 
 		public static readonly FilesystemFilterSet Screenshots = new FilesystemFilterSet(FilesystemFilter.PNGs, new FilesystemFilter(".bmp Files", new[] { "bmp" }));

src/BizHawk.Client.Common/RomLoader.cs

@@ -869,7 +869,7 @@ namespace BizHawk.Client.Common
 		}
 
 		/// <remarks>TODO add and handle <see cref="FilesystemFilter.LuaScripts"/> (you can drag-and-drop scripts and there are already non-rom things in this list, so why not?)</remarks>
-		private static readonly FilesystemFilterSet RomFSFilterSet = new FilesystemFilterSet(
+		public static readonly FilesystemFilterSet RomFilter = new(
 			new FilesystemFilter("Music Files", Array.Empty<string>(), devBuildExtraExts: new[] { "psf", "minipsf", "sid", "nsf", "gbs" }),
 			new FilesystemFilter("Disc Images", new[] { "cue", "ccd", "mds", "m3u" }),
 			new FilesystemFilter("NES", RomFileExtensions.NES.Concat(new[] { "nsf" }).ToList(), addArchiveExts: true),
@@ -905,16 +905,16 @@ namespace BizHawk.Client.Common
 			new FilesystemFilter("Uzebox", RomFileExtensions.UZE),
 			new FilesystemFilter("Vectrex", RomFileExtensions.VEC),
 			new FilesystemFilter("MSX", RomFileExtensions.MSX),
-			FilesystemFilter.EmuHawkSaveStates
-		);
+			FilesystemFilter.EmuHawkSaveStates)
+		{
+			CombinedEntryDesc = "Everything",
+		};
 
-		public static readonly IReadOnlyCollection<string> KnownRomExtensions = RomFSFilterSet.Filters
+		public static readonly IReadOnlyCollection<string> KnownRomExtensions = RomFilter.Filters
 			.SelectMany(f => f.Extensions)
 			.Distinct()
 			.Except(FilesystemFilter.ArchiveExtensions.Concat(new[] { "State" }))
 			.Select(s => $".{s.ToUpperInvariant()}") // this is what's expected at call-site
 			.ToList();
-
-		public static readonly string RomFilter = RomFSFilterSet.ToString("Everything");
 	}
 }

src/BizHawk.Client.Common/movie/import/MovieImport.cs

@@ -27,8 +27,10 @@ namespace BizHawk.Client.Common
 		public static readonly FilesystemFilterSet AvailableImporters = new FilesystemFilterSet(
 			Importers.Values.OrderBy(attr => attr.Emulator)
 				.Select(attr => new FilesystemFilter(attr.Emulator, new[] { attr.Extension.Substring(1) })) // substring removes initial '.'
-				.ToArray()
-		);
+				.ToArray())
+			{
+				CombinedEntryDesc = "Movie Files",
+			};
 
 		// Attempt to import another type of movie file into a movie object.
 		public static ImportResult ImportFile(

src/BizHawk.Client.EmuHawk/MainForm.Events.cs

@@ -302,7 +302,7 @@ namespace BizHawk.Client.EmuHawk
 
 			var args = new LoadRomArgs();
 
-			var filter = RomLoader.RomFilter;
+			var filter = RomLoader.RomFilter.ToString();
 
 			if (oac.Result == AdvancedRomLoaderType.LibretroLaunchGame)
 			{
@@ -494,7 +494,7 @@ namespace BizHawk.Client.EmuHawk
 			{
 				InitialDirectory = Config.PathEntries.RomAbsolutePath(Emulator.SystemId),
 				Multiselect = true,
-				Filter = MovieImport.AvailableImporters.ToString("Movie Files"),
+				Filter = MovieImport.AvailableImporters.ToString(),
 				RestoreDirectory = false
 			};
 

src/BizHawk.Client.EmuHawk/MainForm.cs

@@ -2399,7 +2399,7 @@ namespace BizHawk.Client.EmuHawk
 			using var ofd = new OpenFileDialog
 			{
 				InitialDirectory = Config.PathEntries.RomAbsolutePath(Emulator.SystemId),
-				Filter = RomLoader.RomFilter,
+				Filter = RomLoader.RomFilter.ToString(),
 				RestoreDirectory = false,
 				FilterIndex = _lastOpenRomFilter
 			};

src/BizHawk.Client.EmuHawk/tools/MultiDiskBundler/MultiDiskFileSelector.cs

@@ -75,7 +75,7 @@ namespace BizHawk.Client.EmuHawk
 			using var ofd = new OpenFileDialog
 			{
 				InitialDirectory = _pathEntries.RomAbsolutePath(),
-				Filter = RomLoader.RomFilter,
+				Filter = RomLoader.RomFilter.ToString(),
 				RestoreDirectory = true
 			};