Enable MA0020 and fix noncompliance

"Use direct methods instead of LINQ methods"

Common.ruleset

@@ -171,7 +171,7 @@
 		<Rule Id="MA0019" Action="Error" />
 
 		<!-- Use direct methods instead of LINQ methods -->
-		<Rule Id="MA0020" Action="Hidden" />
+		<Rule Id="MA0020" Action="Error" />
 
 		<!-- Use StringComparer.GetHashCode instead of string.GetHashCode -->
 		<Rule Id="MA0021" Action="Hidden" />

src/BizHawk.Client.Common/config/PathEntryCollection.cs

@@ -120,9 +120,8 @@ namespace BizHawk.Client.Common
 		public IEnumerator<PathEntry> GetEnumerator() => Paths.GetEnumerator();
 		IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
 
-		public PathEntry this[string system, string type] =>
+		public PathEntry this[string system, string type]
-			Paths.FirstOrDefault(p => p.IsSystem(system) && p.Type == type)
+			=> Paths.Find(p => p.IsSystem(system) && p.Type == type) ?? TryGetDebugPath(system, type);
-			?? TryGetDebugPath(system, type);
 
 		private PathEntry TryGetDebugPath(string system, string type)
 		{
@@ -143,11 +142,7 @@ namespace BizHawk.Client.Common
 			// Add missing entries
 			foreach (var defaultPath in Defaults.Value)
 			{
-				var path = Paths.FirstOrDefault(p => p.System == defaultPath.System && p.Type == defaultPath.Type);
+				if (!Paths.Any(p => p.System == defaultPath.System && p.Type == defaultPath.Type)) Paths.Add(defaultPath);
-				if (path == null)
-				{
-					Paths.Add(defaultPath);
-				}
 			}
 
 			var entriesToRemove = new List<PathEntry>();

src/BizHawk.Client.Common/lua/LuaFunctionList.cs

@@ -15,8 +15,8 @@ namespace BizHawk.Client.Common
 
 		public LuaFunctionList(Action onChanged) => Changed = onChanged;
 
-		public NamedLuaFunction this[string guid] =>
+		public NamedLuaFunction this[string guid]
-			_functions.FirstOrDefault(nlf => nlf.Guid.ToString() == guid);
+			=> _functions.Find(nlf => nlf.Guid.ToString() == guid);
 
 		public void Add(NamedLuaFunction nlf)
 		{

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

@@ -68,9 +68,8 @@ namespace BizHawk.Client.Common
 
 		public Cheat this[int index] => _cheatList[index];
 
-		public Cheat this[MemoryDomain domain, long address] =>
+		public Cheat this[MemoryDomain domain, long address]
-			_cheatList.FirstOrDefault(cheat => cheat.Domain == domain && cheat.Address == address);
+			=> _cheatList.Find(cheat => cheat.Domain == domain && cheat.Address == address);
-
 
 		public IEnumerator<Cheat> GetEnumerator() => _cheatList.GetEnumerator();
 

src/BizHawk.Client.EmuHawk/AVOut/NutMuxer.cs

@@ -1,6 +1,5 @@
 using System;
 using System.Collections.Generic;
-using System.Linq;
 using System.Text;
 using System.IO;
 using System.Numerics;
@@ -28,14 +27,14 @@ namespace BizHawk.Client.EmuHawk
 				_capacity = capacity;
 			}
 
-			private T[] GetBufferInternal(int length, bool zerofill, Func<T[], bool> criteria)
+			private T[] GetBufferInternal(int length, bool zerofill, Predicate<T[]> criteria)
 			{
 				if (_inUse.Count == _capacity)
 				{
 					throw new InvalidOperationException();
 				}
 
-				T[] candidate = _available.FirstOrDefault(criteria);
+				var candidate = _available.Find(criteria);
 				if (candidate == null)
 				{
 					if (_available.Count + _inUse.Count == _capacity)

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

@@ -171,9 +171,7 @@ namespace BizHawk.Client.EmuHawk
 		}
 
 		private bool IsDuplicate(string binding)
-		{
+			=> _bindings.Contains(binding);
-			return _bindings.FirstOrDefault(x => x == binding) != null;
-		}
 
 		protected override void OnKeyUp(KeyEventArgs e)
 		{

src/BizHawk.Client.EmuHawk/config/FileExtensionPreferencesPicker.cs

@@ -53,15 +53,10 @@ namespace BizHawk.Client.EmuHawk
 			var selectedSystemId = _preferredPlatformsForExtensions[FileExtension];
 			if (!string.IsNullOrEmpty(selectedSystemId))
 			{
-				var selectedSystem = _availableSystems.FirstOrDefault(s => s.SystemId == selectedSystemId);
+				var selectedSystem = _availableSystems.Find(s => s.SystemId == selectedSystemId)?.FullName ?? string.Empty;
-
+				if (PlatformDropdown.Items.Contains(selectedSystem))
-				var selectedItem = PlatformDropdown.Items
-					.OfType<string>()
-					.FirstOrDefault(item => item == (selectedSystem?.FullName ?? ""));
-
-				if (selectedItem != null)
 				{
-					PlatformDropdown.SelectedItem = selectedItem;
+					PlatformDropdown.SelectedItem = selectedSystem;
 				}
 				else
 				{

src/BizHawk.Client.EmuHawk/tools/Lua/Libraries/FormsLuaLibrary.cs

@@ -25,14 +25,14 @@ namespace BizHawk.Client.EmuHawk
 
 		public void WindowClosed(IntPtr handle)
 		{
-			var form = _luaForms.FirstOrDefault(form => form.Handle == handle);
+			var i = _luaForms.FindIndex(form => form.Handle == handle);
-			if (form != null) _luaForms.Remove(form);
+			if (i is not -1) _luaForms.RemoveAt(i);
 		}
 
 		private LuaWinform GetForm(int formHandle)
 		{
 			var ptr = new IntPtr(formHandle);
-			return _luaForms.FirstOrDefault(form => form.Handle == ptr);
+			return _luaForms.Find(form => form.Handle == ptr);
 		}
 
 		private static void SetLocation(Control control, int x, int y)

src/BizHawk.Client.EmuHawk/tools/ToolManager.cs

@@ -455,21 +455,10 @@ namespace BizHawk.Client.EmuHawk
 		/// </summary>
 		/// <typeparam name="T">Type of tool to check</typeparam>
 		public bool IsLoaded<T>() where T : IToolForm
-		{
+			=> _tools.OfType<T>().FirstOrDefault()?.IsActive is true;
-			var existingTool = _tools.FirstOrDefault(t => t is T);
-			if (existingTool != null)
-			{
-				return existingTool.IsActive;
-			}
-
-			return false;
-		}
 
 		public bool IsLoaded(Type toolType)
-		{
+			=> _tools.Find(t => t.GetType() == toolType)?.IsActive is true;
-			var existingTool = _tools.FirstOrDefault(t => t.GetType() == toolType);
-			return existingTool != null && existingTool.IsActive;
-		}
 
 		public bool IsOnScreen(Point topLeft)
 		{
@@ -511,8 +500,8 @@ namespace BizHawk.Client.EmuHawk
 		/// <typeparam name="T">Type of tool to update</typeparam>
 		public void UpdateValues<T>() where T : IToolForm
 		{
-			var tool = _tools.FirstOrDefault(t => t is T);
+			var tool = _tools.OfType<T>().FirstOrDefault();
-			if (tool != null && tool.IsActive)
+			if (tool?.IsActive is true)
 			{
 				tool.UpdateValues(ToolFormUpdateType.General);
 			}
@@ -568,10 +557,7 @@ namespace BizHawk.Client.EmuHawk
 		/// </summary>
 		/// <typeparam name="T">Type of tool to restart</typeparam>
 		public void Restart<T>() where T : IToolForm
-		{
+			=> _tools.OfType<T>().FirstOrDefault()?.Restart();
-			var tool = _tools.FirstOrDefault(t => t is T);
-			tool?.Restart();
-		}
 
 		/// <summary>
 		/// Runs AskSave on every tool dialog, false is returned if any tool returns false
@@ -594,7 +580,7 @@ namespace BizHawk.Client.EmuHawk
 		/// <typeparam name="T">Type of tool to close</typeparam>
 		public void Close<T>() where T : IToolForm
 		{
-			var tool = _tools.FirstOrDefault(t => t is T);
+			var tool = _tools.OfType<T>().FirstOrDefault();
 			if (tool != null)
 			{
 				tool.Close();
@@ -604,8 +590,7 @@ namespace BizHawk.Client.EmuHawk
 
 		public void Close(Type toolType)
 		{
-			var tool = _tools.FirstOrDefault(toolType.IsInstanceOfType);
+			var tool = _tools.Find(toolType.IsInstanceOfType);
-
 			if (tool != null)
 			{
 				tool.Close();

src/BizHawk.Client.EmuHawk/tools/Watch/RamSearch.cs

@@ -346,8 +346,7 @@ namespace BizHawk.Client.EmuHawk
 				.OrderBy(x => x.TabIndex)
 				.ToList();
 
-			var selected = radios.FirstOrDefault(x => x.Checked);
+			var index = radios.FindIndex(static x => x.Checked);
-			var index = radios.IndexOf(selected);
 
 			if (reverse)
 			{
@@ -382,8 +381,7 @@ namespace BizHawk.Client.EmuHawk
 				.OrderBy(x => x.TabIndex)
 				.ToList();
 
-			var selected = radios.FirstOrDefault(x => x.Checked);
+			var index = radios.FindIndex(static x => x.Checked);
-			var index = radios.IndexOf(selected);
 
 			if (reverse)
 			{

src/BizHawk.Emulation.Common/SystemLookup.cs

@@ -1,5 +1,4 @@
 using System.Collections.Generic;
-using System.Linq;
 
 namespace BizHawk.Emulation.Common
 {
@@ -38,8 +37,7 @@ namespace BizHawk.Emulation.Common
 		};
 
 		public SystemInfo this[string systemId]
-			=> _systems.FirstOrDefault(s => s.SystemId == systemId)
+			=> _systems.Find(s => s.SystemId == systemId) ?? new("Unknown", "Unknown");
-			?? new SystemInfo("Unknown", "Unknown");
 
 		public IEnumerable<SystemInfo> AllSystems => _systems;
 

src/BizHawk.Emulation.Cores/Computers/AmstradCPC/Hardware/Disk/NECUPD765.FDC.cs

@@ -2493,9 +2493,8 @@ namespace BizHawk.Emulation.Cores.Computers.AmstradCPC
 			cmdByte = cByte;
 
 			// lookup the command
-			var cmd = CommandList.FirstOrDefault(a => a.CommandCode == cmdByte);
+			var i = CommandList.FindIndex(a => a.CommandCode == cmdByte);
-
+			if (i is -1)
-			if (cmd == null)
 			{
 				// no command found - use invalid
 				CMDIndex = CommandList.Count - 1;
@@ -2503,7 +2502,7 @@ namespace BizHawk.Emulation.Cores.Computers.AmstradCPC
 			else
 			{
 				// valid command found
-				CMDIndex = CommandList.FindIndex(a => a.CommandCode == cmdByte);
+				CMDIndex = i;
 
 				// check validity of command byte flags
 				// if a flag is set but not valid for this command then it is invalid

src/BizHawk.Emulation.Cores/Computers/SinclairSpectrum/Hardware/Disk/NECUPD765.FDC.cs

@@ -2517,9 +2517,8 @@ namespace BizHawk.Emulation.Cores.Computers.SinclairSpectrum
 			cmdByte = cByte;
 
 			// lookup the command
-			var cmd = CommandList.FirstOrDefault(a => a.CommandCode == cmdByte);
+			var i = CommandList.FindIndex(a => a.CommandCode == cmdByte);
-
+			if (i is -1)
-			if (cmd == null)
 			{
 				// no command found - use invalid
 				CMDIndex = CommandList.Count - 1;
@@ -2527,7 +2526,7 @@ namespace BizHawk.Emulation.Cores.Computers.SinclairSpectrum
 			else
 			{
 				// valid command found
-				CMDIndex = CommandList.FindIndex(a => a.CommandCode == cmdByte);
+				CMDIndex = i;
 
 				// check validity of command byte flags
 				// if a flag is set but not valid for this command then it is invalid

src/BizHawk.Emulation.Cores/Computers/SinclairSpectrum/Media/Disk/IPFFormat/IPFFloppyDisk.cs

@@ -62,7 +62,7 @@ namespace BizHawk.Emulation.Cores.Computers.SinclairSpectrum
 			}
 
 			// now process the blocks
-			var infoBlock = blocks.FirstOrDefault(a => a.RecordType == RecordHeaderType.INFO);
+			var infoBlock = blocks.Find(static a => a.RecordType == RecordHeaderType.INFO);
 			var IMGEblocks = blocks.Where(a => a.RecordType == RecordHeaderType.IMGE).ToList();
 			var DATAblocks = blocks.Where(a => a.RecordType == RecordHeaderType.DATA);
 

src/BizHawk.Emulation.Cores/Waterbox/NymaCore.Controller.cs

@@ -72,13 +72,12 @@ namespace BizHawk.Emulation.Cores.Waterbox
 
 					var devices = portInfo.Devices;
 					
-					var device = devices.FirstOrDefault(a => a.ShortName == deviceName);
+					var device = devices.Find(a => a.ShortName == deviceName);
 					if (device == null)
 					{
 						Console.WriteLine($"Warn: unknown controller device {deviceName}");
-						device = devices.FirstOrDefault(a => a.ShortName == portInfo.DefaultDeviceShortName);
+						device = devices.Find(a => a.ShortName == portInfo.DefaultDeviceShortName)
-						if (device == null)
+							?? throw new InvalidOperationException($"Fail: unknown controller device {portInfo.DefaultDeviceShortName}");
-							throw new InvalidOperationException($"Fail: unknown controller device {portInfo.DefaultDeviceShortName}");
 					}
 
 					ActualPortData.Add(new PortResult

src/BizHawk.Emulation.DiscSystem/DiscFormats/Blobs/Blob_WaveFile.cs

@@ -50,7 +50,7 @@ namespace BizHawk.Emulation.DiscSystem
 					throw new Blob_WaveFile_Exception("Not a RIFF WAVE file");
 				}
 
-				if (!(rm.riff.subchunks.FirstOrDefault(chunk => chunk.tag == "fmt ") is RiffMaster.RiffSubchunk_fmt fmt))
+				if (rm.riff.subchunks.Find(static chunk => chunk.tag == "fmt ") is not RiffMaster.RiffSubchunk_fmt fmt)
 				{
 					throw new Blob_WaveFile_Exception("Not a valid RIFF WAVE file (missing fmt chunk");
 				}