Add Analyzer to disallow ^= true

.global.editorconfig.ini

@@ -22,6 +22,8 @@ dotnet_diagnostic.BHI1101.severity = error
 dotnet_diagnostic.BHI1102.severity = error
 # Don't call typeof(T).ToString(), use nameof operator or typeof(T).FullName
 dotnet_diagnostic.BHI1103.severity = error
+# Don't use ^= (XOR-assign) for inverting the value of booleans
+dotnet_diagnostic.BHI1104.severity = error
 # Brackets of collection expression should be separated with spaces
 dotnet_diagnostic.BHI1110.severity = warning
 # Expression-bodied member should be flowed to next line correctly

ExternalProjects/BizHawk.Analyzer/UseSimplerBoolFlipAnalyzer.cs

@@ -0,0 +1,79 @@
+namespace BizHawk.Analyzers;
+
+using System.Collections.Immutable;
+
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.Diagnostics;
+using Microsoft.CodeAnalysis.Operations;
+
+/// <remarks>shoutouts to SimpleFlips</remarks>
+[DiagnosticAnalyzer(LanguageNames.CSharp)]
+public sealed class UseSimplerBoolFlipAnalyzer : DiagnosticAnalyzer
+{
+	private const string ERR_MSG_SIMPLE = "Use e.g. `b = !b;` instead of `b ^= true;`";
+
+	private const string ERR_MSG_COMPLEX = $"{ERR_MSG_SIMPLE} (you may want to store part of the expression in a local variable to avoid repeated side-effects or computation)";
+
+	private static readonly DiagnosticDescriptor DiagUseSimplerBoolFlip = new(
+		id: "BHI1104",
+		title: "Don't use ^= (XOR-assign) for inverting the value of booleans",
+		messageFormat: "{0}",
+		category: "Usage",
+		defaultSeverity: DiagnosticSeverity.Error,
+		isEnabledByDefault: true);
+
+	public override ImmutableArray<DiagnosticDescriptor> SupportedDiagnostics { get; } = ImmutableArray.Create(DiagUseSimplerBoolFlip);
+
+	public override void Initialize(AnalysisContext context)
+	{
+		context.ConfigureGeneratedCodeAnalysis(GeneratedCodeAnalysisFlags.None);
+		context.EnableConcurrentExecution();
+		ISymbol? boolSym = null;
+		context.RegisterOperationAction(
+			oac =>
+			{
+				static bool IsZeroWorkLocalOrFieldRef(IOperation trunk)
+				{
+					while (trunk.Kind is OperationKind.FieldReference)
+					{
+						if (trunk.ChildOperations.Count is 0) return true; // in the unit test, the node(s) for the implicit `this.` are missing for some reason
+						trunk = trunk.ChildOperations.First();
+					}
+					return trunk.Kind is OperationKind.InstanceReference or OperationKind.LocalReference;
+				}
+				var operation = (ICompoundAssignmentOperation) oac.Operation;
+				if (operation.OperatorKind is not BinaryOperatorKind.ExclusiveOr) return;
+				boolSym ??= oac.Compilation.GetTypeByMetadataName("System.Boolean")!;
+				if (!boolSym.Matches(operation.Type)) return;
+				if (operation.Value.Kind is not OperationKind.Literal) return;
+				var lhsOp = operation.Target;
+				bool lhsIsSimpleExpr;
+				switch (lhsOp.Kind)
+				{
+					case OperationKind.PropertyReference:
+						lhsIsSimpleExpr = false;
+						break;
+					case OperationKind.FieldReference:
+						lhsIsSimpleExpr = IsZeroWorkLocalOrFieldRef(lhsOp);
+						break;
+					case OperationKind.LocalReference:
+						lhsIsSimpleExpr = true;
+						break;
+					case OperationKind.ArrayElementReference:
+						lhsIsSimpleExpr = false;
+						break;
+					default:
+						oac.ReportDiagnostic(Diagnostic.Create(DiagUseSimplerBoolFlip, operation.Syntax.GetLocation(), $"Left-hand side of XOR-assign was of an unexpected kind: {lhsOp.GetType().FullName}"));
+						return;
+				}
+				oac.ReportDiagnostic(Diagnostic.Create(
+					DiagUseSimplerBoolFlip,
+					operation.Syntax.GetLocation(),
+					lhsIsSimpleExpr ? DiagnosticSeverity.Error : DiagnosticSeverity.Warning,
+					additionalLocations: null,
+					properties: null,
+					lhsIsSimpleExpr ? ERR_MSG_SIMPLE : ERR_MSG_COMPLEX));
+			},
+			OperationKind.CompoundAssignment);
+	}
+}

ExternalProjects/BizHawk.AnalyzersTests/BizHawk.Analyzer/UseSimplerBoolFlipAnalyzerTests.cs

@@ -0,0 +1,40 @@
+namespace BizHawk.Tests.Analyzers;
+
+using System.Threading.Tasks;
+
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+using Verify = Microsoft.CodeAnalysis.CSharp.Testing.CSharpAnalyzerVerifier<
+	BizHawk.Analyzers.UseSimplerBoolFlipAnalyzer,
+	Microsoft.CodeAnalysis.Testing.DefaultVerifier>;
+
+[TestClass]
+public sealed class UseSimplerBoolFlipAnalyzerTests
+{
+	[TestMethod]
+	public Task CheckMisuseOfXORAssignment()
+		=> Verify.VerifyAnalyzerAsync("""
+			public static class Cases {
+				private static int _z = default;
+				private static bool _a = default;
+				private static void CasesMethod() {
+					_z ^= 0xA5A5;
+					_a ^= DummyMethod();
+					{|BHI1104:_a ^= true|};
+					var b = false;
+					{|BHI1104:b ^= true|};
+					bool c = default;
+					{|BHI1104:c ^= false|}; // this is effectively a no-op so there's no reason it would be used in the first place, but it was easier to flag both
+					{|BHI1104:AnotherClass.GetInstance().Prop ^= true|}; // care needs to be taken with non-trivial expressions like this; a different message will be given
+				}
+				private static bool DummyMethod()
+					=> default;
+			}
+			public sealed class AnotherClass {
+				public static AnotherClass GetInstance()
+					=> new();
+				public bool Prop { get; set; }
+				private AnotherClass() {}
+			}
+		""");
+}

src/BizHawk.Client.Common/Controller.cs

@@ -147,10 +147,7 @@ public void Overrides(OverrideAdapter controller)
 				_axes[button] = controller.AxisValue(button);
 			}
 
-			foreach (var button in controller.InversedButtons)
-			{
-				_buttons[button] ^= true;
-			}
+			foreach (var button in controller.InversedButtons) _buttons[button] = !_buttons[button];
 		}
 
 		public void BindMulti(string button, string controlString)

src/BizHawk.Client.Common/RecentFiles.cs

@@ -74,8 +74,6 @@ public bool Remove(string newFile)
 		}
 
 		public void ToggleAutoLoad()
-		{
-			AutoLoad ^= true;
-		}
+			=> AutoLoad = !AutoLoad;
 	}
 }

src/BizHawk.Client.Common/SaveSlotManager.cs

@@ -67,7 +67,7 @@ public void ClearRedoList()
 
 		public void ToggleRedo(IMovie movie, int slot)
 		{
-			if (slot is >= 1 and <= 10 && movie is not ITasMovie) _redo[slot - 1] ^= true;
+			if (slot is >= 1 and <= 10 && movie is not ITasMovie) _redo[slot - 1] = !_redo[slot - 1];
 		}
 
 		public bool IsRedo(IMovie movie, int slot)

src/BizHawk.Client.Common/tools/Cheat.cs

@@ -149,7 +149,7 @@ public void Toggle(bool handleChange = true)
 		{
 			if (!IsSeparator)
 			{
-				_enabled ^= true;
+				_enabled = !_enabled;
 				if (handleChange)
 				{
 					Changes();

src/BizHawk.Client.EmuHawk/CustomControls/InputRoll/InputRoll.cs

@@ -988,7 +988,7 @@ public IEnumerable<ToolStripItem> GenerateContextMenuItems()
 					ShortcutKeyDisplayString = RotateHotkeyStr
 				};
 
-				rotate.Click += (o, ev) => { HorizontalOrientation ^= true; };
+				rotate.Click += (_, _) => HorizontalOrientation = !HorizontalOrientation;
 
 				yield return rotate;
 			}
@@ -1372,10 +1372,7 @@ protected override void OnKeyDown(KeyEventArgs e)
 				}
 				else if (e.IsCtrlShift(Keys.F))
 				{
-					if (Rotatable)
-					{
-						HorizontalOrientation ^= true;
-					}
+					if (Rotatable) HorizontalOrientation = !HorizontalOrientation;
 				}
 				// Scroll
 				else if (e.IsPressed(Keys.PageUp))

src/BizHawk.Client.EmuHawk/Extensions/ToolExtensions.cs

@@ -189,7 +189,7 @@ public static class ToolExtensions
 				Text = recent.Frozen ? "&Unfreeze" : "&Freeze",
 				Image = recent.Frozen ? Properties.Resources.Unfreeze : Properties.Resources.Freeze
 			};
-			freezeItem.Click += (o, ev) => recent.Frozen ^= true;
+			freezeItem.Click += (_, _) => recent.Frozen = !recent.Frozen;
 			items.Add(freezeItem);
 
 			if (!noAutoload)

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

@@ -359,13 +359,10 @@ private void QuickLoadstateMenuItem_Click(object sender, EventArgs e)
 		private void LoadNamedStateMenuItem_Click(object sender, EventArgs e) => LoadStateAs();
 
 		private void AutoloadLastSlotMenuItem_Click(object sender, EventArgs e)
-		{
-			Config.AutoLoadLastSaveSlot ^= true;
-		}
+			=> Config.AutoLoadLastSaveSlot = !Config.AutoLoadLastSaveSlot;
+
 		private void AutosaveLastSlotMenuItem_Click(object sender, EventArgs e)
-		{
-			Config.AutoSaveLastSaveSlot ^= true;
-		}
+			=> Config.AutoSaveLastSaveSlot = !Config.AutoSaveLastSaveSlot;
 
 		private void SelectSlotMenuItems_Click(object sender, EventArgs e)
 		{
@@ -510,14 +507,10 @@ private void StopMovieWithoutSavingMenuItem_Click(object sender, EventArgs e)
 		}
 
 		private void AutomaticMovieBackupMenuItem_Click(object sender, EventArgs e)
-		{
-			Config.Movies.EnableBackupMovies ^= true;
-		}
+			=> Config.Movies.EnableBackupMovies = !Config.Movies.EnableBackupMovies;
 
 		private void FullMovieLoadstatesMenuItem_Click(object sender, EventArgs e)
-		{
-			Config.Movies.VBAStyleMovieLoadState ^= true;
-		}
+			=> Config.Movies.VBAStyleMovieLoadState = !Config.Movies.VBAStyleMovieLoadState;
 
 		private void MovieEndFinishMenuItem_Click(object sender, EventArgs e)
 		{
@@ -601,9 +594,7 @@ private void ScreenshotClientClipboardMenuItem_Click(object sender, EventArgs e)
 		}
 
 		private void ScreenshotCaptureOSDMenuItem_Click(object sender, EventArgs e)
-		{
-			Config.ScreenshotCaptureOsd ^= true;
-		}
+			=> Config.ScreenshotCaptureOsd = !Config.ScreenshotCaptureOsd;
 
 		private void ExitMenuItem_Click(object sender, EventArgs e)
 		{
@@ -728,25 +719,19 @@ private void DisplayInputMenuItem_Click(object sender, EventArgs e)
 		}
 
 		private void DisplayRerecordsMenuItem_Click(object sender, EventArgs e)
-		{
-			Config.DisplayRerecordCount ^= true;
-		}
+			=> Config.DisplayRerecordCount = !Config.DisplayRerecordCount;
 
 		private void DisplaySubtitlesMenuItem_Click(object sender, EventArgs e)
-		{
-			Config.DisplaySubtitles ^= true;
-		}
+			=> Config.DisplaySubtitles = !Config.DisplaySubtitles;
 
 		private void DisplayStatusBarMenuItem_Click(object sender, EventArgs e)
 		{
-			Config.DispChromeStatusBarWindowed ^= true;
+			Config.DispChromeStatusBarWindowed = !Config.DispChromeStatusBarWindowed;
 			SetStatusBar();
 		}
 
 		private void DisplayMessagesMenuItem_Click(object sender, EventArgs e)
-		{
-			Config.DisplayMessages ^= true;
-		}
+			=> Config.DisplayMessages = !Config.DisplayMessages;
 
 		private void DisplayLogWindowMenuItem_Click(object sender, EventArgs e)
 		{
@@ -959,7 +944,7 @@ private void ProfilesMenuItem_Click(object sender, EventArgs e)
 
 		private void ClockThrottleMenuItem_Click(object sender, EventArgs e)
 		{
-			Config.ClockThrottle ^= true;
+			Config.ClockThrottle = !Config.ClockThrottle;
 			if (Config.ClockThrottle)
 			{
 				var old = Config.SoundThrottle;
@@ -982,7 +967,7 @@ private void ClockThrottleMenuItem_Click(object sender, EventArgs e)
 
 		private void AudioThrottleMenuItem_Click(object sender, EventArgs e)
 		{
-			Config.SoundThrottle ^= true;
+			Config.SoundThrottle = !Config.SoundThrottle;
 			RewireSound();
 			if (Config.SoundThrottle)
 			{
@@ -1000,7 +985,7 @@ private void AudioThrottleMenuItem_Click(object sender, EventArgs e)
 
 		private void VsyncThrottleMenuItem_Click(object sender, EventArgs e)
 		{
-			Config.VSyncThrottle ^= true;
+			Config.VSyncThrottle = !Config.VSyncThrottle;
 			_presentationPanel.Resized = true;
 			if (Config.VSyncThrottle)
 			{
@@ -1024,7 +1009,7 @@ private void VsyncThrottleMenuItem_Click(object sender, EventArgs e)
 
 		private void VsyncEnabledMenuItem_Click(object sender, EventArgs e)
 		{
-			Config.VSync ^= true;
+			Config.VSync = !Config.VSync;
 			if (!Config.VSyncThrottle) // when vsync throttle is on, vsync is forced to on, so no change to make here
 			{
 				_presentationPanel.Resized = true;
@@ -1038,14 +1023,12 @@ private void UnthrottledMenuItem_Click(object sender, EventArgs e)
 
 		private void ToggleUnthrottled()
 		{
-			Config.Unthrottled ^= true;
+			Config.Unthrottled = !Config.Unthrottled;
 			ThrottleMessage();
 		}
 
 		private void MinimizeSkippingMenuItem_Click(object sender, EventArgs e)
-		{
-			Config.AutoMinimizeSkipping ^= true;
-		}
+			=> Config.AutoMinimizeSkipping = !Config.AutoMinimizeSkipping;
 
 		private void NeverSkipMenuItem_Click(object sender, EventArgs e) { Config.FrameSkip = 0; FrameSkipMessage(); }
 		private void Frameskip1MenuItem_Click(object sender, EventArgs e) { Config.FrameSkip = 1; FrameSkipMessage(); }
@@ -1781,9 +1764,7 @@ private void N64ControllerSettingsMenuItem_Click(object sender, EventArgs e)
 		}
 
 		private void N64CircularAnalogRangeMenuItem_Click(object sender, EventArgs e)
-		{
-			Config.N64UseCircularAnalogConstraint ^= true;
-		}
+			=> Config.N64UseCircularAnalogConstraint = !Config.N64UseCircularAnalogConstraint;
 
 		private static void Mupen64PlusSetMupenStyleLag(bool newValue, ISettingsAdapter settable)
 		{
@@ -2450,7 +2431,7 @@ private void ClearSramContextMenuItem_Click(object sender, EventArgs e)
 
 		private void ShowMenuContextMenuItem_Click(object sender, EventArgs e)
 		{
-			MainMenuStrip.Visible ^= true;
+			MainMenuStrip.Visible = !MainMenuStrip.Visible;
 			FrameBufferResized();
 		}
 
@@ -2558,8 +2539,9 @@ private void LinkConnectStatusBarButton_Click(object sender, EventArgs e)
 			// toggle Link status (only outside of a movie session)
 			if (!MovieSession.Movie.IsPlaying())
 			{
-				Emulator.AsLinkable().LinkConnected ^= true;
-				Console.WriteLine("Cable connect status to {0}", Emulator.AsLinkable().LinkConnected);
+				var core = Emulator.AsLinkable();
+				core.LinkConnected = !core.LinkConnected;
+				Console.WriteLine($"Cable connect status to {core.LinkConnected}");
 			}
 		}
 

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

@@ -151,7 +151,7 @@ void SelectAndLoadFromSlot(int slot)
 					RebootCore();
 					break;
 				case "Toggle Skip Lag Frame":
-					Config.SkipLagFrame ^= true;
+					Config.SkipLagFrame = !Config.SkipLagFrame;
 					AddOnScreenMessage($"Skip Lag Frames toggled {(Config.SkipLagFrame ? "On" : "Off")}");
 					break;
 				case "Toggle Key Priority":
@@ -382,15 +382,18 @@ void SelectAndLoadFromSlot(int slot)
 					break;
 				case "Toggle Follow Cursor":
 					if (!Tools.IsLoaded<TAStudio>()) return false;
-					Tools.TAStudio.TasPlaybackBox.FollowCursor ^= true;
+					var playbackBox = Tools.TAStudio.TasPlaybackBox;
+					playbackBox.FollowCursor = !playbackBox.FollowCursor;
 					break;
 				case "Toggle Auto-Restore":
 					if (!Tools.IsLoaded<TAStudio>()) return false;
-					Tools.TAStudio.TasPlaybackBox.AutoRestore ^= true;
+					var playbackBox1 = Tools.TAStudio.TasPlaybackBox;
+					playbackBox1.AutoRestore = !playbackBox1.AutoRestore;
 					break;
 				case "Toggle Turbo Seek":
 					if (!Tools.IsLoaded<TAStudio>()) return false;
-					Tools.TAStudio.TasPlaybackBox.TurboSeek ^= true;
+					var playbackBox2 = Tools.TAStudio.TasPlaybackBox;
+					playbackBox2.TurboSeek = !playbackBox2.TurboSeek;
 					break;
 				case "Undo":
 					if (!Tools.IsLoaded<TAStudio>()) return false;

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

@@ -129,7 +129,7 @@ private void ToggleReadOnly()
 			{
 				if (MovieSession.Movie.IsActive())
 				{
-					MovieSession.ReadOnly ^= true;
+					MovieSession.ReadOnly = !MovieSession.ReadOnly;
 					AddOnScreenMessage(MovieSession.ReadOnly ? "Movie read-only mode" : "Movie read+write mode");
 				}
 				else