Backport `IEnumerable.Order`/`OrderDescending` shorthand

at time of writing, in .NET 7 preview
https://github.com/dotnet/runtime/pull/70525

Common.ruleset

@@ -31,6 +31,9 @@
 		<!-- Call to FirstOrDefault when elements are of a value type; FirstOrNull may have been intended -->
 		<Rule Id="BHI3100" Action="Error" />
 
+		<!-- Use .Order()/.OrderDescending() shorthand -->
+		<Rule Id="BHI3101" Action="Warning" />
+
 		<!-- Throw NotImplementedException from methods/props marked [FeatureNotImplemented] -->
 		<Rule Id="BHI3300" Action="Error" />
 	</Rules>

ExternalProjects/BizHawk.Analyzer/OrderBySelfAnalyzer.cs

@@ -0,0 +1,70 @@
+namespace BizHawk.Analyzers;
+
+using System.Collections.Immutable;
+using System.Linq;
+
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.CSharp.Syntax;
+using Microsoft.CodeAnalysis.Diagnostics;
+using Microsoft.CodeAnalysis.Operations;
+
+[DiagnosticAnalyzer(LanguageNames.CSharp)]
+public class OrderBySelfAnalyzer : DiagnosticAnalyzer
+{
+	private static readonly DiagnosticDescriptor DiagUseOrderBySelfExt = new(
+		id: "BHI3101",
+		title: "Use .Order()/.OrderDescending() shorthand",
+		messageFormat: "Replace .OrderBy{0}(e => e) with .Order{0}()",
+		category: "Usage",
+		defaultSeverity: DiagnosticSeverity.Warning,
+		isEnabledByDefault: true);
+
+	public override ImmutableArray<DiagnosticDescriptor> SupportedDiagnostics { get; } = ImmutableArray.Create(DiagUseOrderBySelfExt);
+
+	public override void Initialize(AnalysisContext context)
+	{
+		context.ConfigureGeneratedCodeAnalysis(GeneratedCodeAnalysisFlags.None);
+		context.EnableConcurrentExecution();
+		context.RegisterCompilationStartAction(initContext =>
+		{
+			if (initContext.Compilation.GetTypeByMetadataName("BizHawk.Common.CollectionExtensions.CollectionExtensions") is null) return; // project does not have BizHawk.Common dependency
+			var linqExtClassSym = initContext.Compilation.GetTypeByMetadataName("System.Linq.Enumerable")!;
+			var orderByAscSym = linqExtClassSym.GetMembers("OrderBy").Cast<IMethodSymbol>().First(sym => sym.Parameters.Length is 2);
+			var orderByDescSym = linqExtClassSym.GetMembers("OrderByDescending").Cast<IMethodSymbol>().First(sym => sym.Parameters.Length is 2);
+			initContext.RegisterOperationAction(
+				oac =>
+				{
+					static bool IsSelfReturnLambda(AnonymousFunctionExpressionSyntax afes)
+					{
+						ParameterSyntax paramSyn;
+						switch (afes)
+						{
+							case AnonymousMethodExpressionSyntax ames: // banned in BizHawk but included for completeness
+								if ((ames.ParameterList?.Parameters)?.Count is not 1) return false;
+								paramSyn = ames.ParameterList.Parameters[0];
+								break;
+							case ParenthesizedLambdaExpressionSyntax ples:
+								if (ples.ParameterList.Parameters.Count is not 1) return false;
+								paramSyn = ples.ParameterList.Parameters[0];
+								break;
+							case SimpleLambdaExpressionSyntax sles:
+								paramSyn = sles.Parameter;
+								break;
+							default:
+								return false;
+						}
+						bool Matches(IdentifierNameSyntax ins)
+							=> ins.Identifier.ValueText == paramSyn.Identifier.ValueText;
+						if (afes.ExpressionBody is not null) return afes.ExpressionBody is IdentifierNameSyntax ins && Matches(ins);
+						return afes.Block!.Statements.Count is 1 && afes.Block.Statements[0] is ReturnStatementSyntax { Expression: IdentifierNameSyntax ins1 } && Matches(ins1);
+					}
+					var operation = (IInvocationOperation) oac.Operation;
+					var calledSym = operation.TargetMethod.ConstructedFrom;
+					if (!(orderByAscSym!.Matches(calledSym) || orderByDescSym!.Matches(calledSym))) return;
+					if (((ArgumentSyntax) operation.Arguments[1].Syntax).Expression is not AnonymousFunctionExpressionSyntax afes) return;
+					if (IsSelfReturnLambda(afes)) oac.ReportDiagnostic(Diagnostic.Create(DiagUseOrderBySelfExt, afes.GetLocation(), orderByDescSym.Matches(calledSym) ? "Descending" : string.Empty));
+				},
+				OperationKind.Invocation);
+		});
+	}
+}

src/BizHawk.Client.Common/ArgParser.cs

@@ -5,6 +5,8 @@ using System.Collections.Generic;
 using System.Linq;
 using System.IO;
 
+using BizHawk.Common.CollectionExtensions;
+
 namespace BizHawk.Client.Common
 {
 	/// <summary>
@@ -86,7 +88,7 @@ namespace BizHawk.Client.Common
 					}
 
 					// automatically set dump length to maximum frame
-					autoDumpLength = currAviWriterFrameList.OrderBy(x => x).Last();
+					autoDumpLength = currAviWriterFrameList.Order().Last();
 				}
 				else if (argDowncased.StartsWith("--version"))
 				{

src/BizHawk.Client.Common/FilesystemFilterSet.cs

@@ -3,6 +3,8 @@
 using System.Collections.Generic;
 using System.Linq;
 
+using BizHawk.Common.CollectionExtensions;
+
 namespace BizHawk.Client.Common
 {
 	public sealed class FilesystemFilterSet
@@ -27,7 +29,7 @@ namespace BizHawk.Client.Common
 		/// <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().OrderBy(static s => s).ToList());
+			_allSer ??= FilesystemFilter.SerializeEntry(combinedEntryDesc, Filters.SelectMany(static filter => filter.Extensions).Distinct().Order().ToList());
 			return $"{_allSer}|{ToString(addAllFilesEntry)}";
 		}
 

src/BizHawk.Client.Common/movie/tasproj/TasMovie.Editing.cs

@@ -2,6 +2,7 @@
 using System.Collections.Generic;
 using System.Linq;
 
+using BizHawk.Common.CollectionExtensions;
 using BizHawk.Emulation.Common;
 
 namespace BizHawk.Client.Common
@@ -117,8 +118,7 @@ namespace BizHawk.Client.Common
 				// and process each block independently
 				List<int> framesToDelete = frames
 					.Where(fr => fr >= 0 && fr < InputLogLength)
-					.OrderBy(fr => fr)
-					.ToList();
+					.Order().ToList();
 				// f is the current index for framesToDelete
 				int f = 0;
 				int numDeleted = 0;

src/BizHawk.Client.Common/movie/tasproj/ZwinderStateManager.cs

@@ -3,6 +3,7 @@ using System.Collections.Generic;
 using System.IO;
 using System.Linq;
 using BizHawk.Common;
+using BizHawk.Common.CollectionExtensions;
 using BizHawk.Emulation.Common;
 
 namespace BizHawk.Client.Common
@@ -244,7 +245,7 @@ namespace BizHawk.Client.Common
 		// Enumerate all reserved states in reverse order
 		private IEnumerable<StateInfo> ReservedStates()
 		{
-			foreach (var key in _reserved.Keys.OrderByDescending(k => k))
+			foreach (var key in _reserved.Keys.OrderDescending())
 			{
 				yield return new StateInfo(key, _reserved[key]);
 			}

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

@@ -3,6 +3,8 @@ using System.Linq;
 using System.Text;
 
 using BizHawk.Client.Common;
+using BizHawk.Common.CollectionExtensions;
+
 using NLua;
 
 namespace BizHawk.Client.EmuHawk
@@ -82,7 +84,7 @@ namespace BizHawk.Client.EmuHawk
 
 				return string.Concat(keyObjs.Cast<object>()
 					.Select((kObj, i) => $"\"{(kObj is string s ? FixString(s) : kObj.ToString())}\": \"{(values[i] is string s1 ? FixString(s1) : values[i].ToString())}\"\n")
-					.OrderBy(static s => s));
+					.Order());
 			}
 
 			if (!Tools.Has<LuaConsole>())

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

@@ -759,7 +759,7 @@ namespace BizHawk.Client.EmuHawk
 		private void RemoveWatchMenuItem_Click(object sender, EventArgs e)
 		{
 			if (!WatchListView.AnyRowsSelected) return;
-			foreach (var index in SelectedIndices.OrderByDescending(static i => i).ToList()) _watches.RemoveAt(index);
+			foreach (var index in SelectedIndices.OrderDescending().ToList()) _watches.RemoveAt(index);
 			WatchListView.RowCount = _watches.Count;
 			GeneralUpdate();
 			UpdateWatchCount();

src/BizHawk.Common/Extensions/CollectionExtensions.cs

@@ -2,6 +2,7 @@
 using System.Collections;
 using System.Collections.Generic;
 using System.Linq;
+using System.Runtime.CompilerServices;
 
 namespace BizHawk.Common.CollectionExtensions
 {
@@ -153,6 +154,16 @@ namespace BizHawk.Common.CollectionExtensions
 			return null;
 		}
 
+		/// <remarks>shorthand for <c>this.OrderBy(static e => e)</c>, backported from .NET 7</remarks>
+		public static IOrderedEnumerable<T> Order<T>(this IEnumerable<T> source)
+			where T : IComparable<T>
+			=> source.OrderBy(ReturnSelf);
+
+		/// <remarks>shorthand for <c>this.OrderByDescending(static e => e)</c>, backported from .NET 7</remarks>
+		public static IOrderedEnumerable<T> OrderDescending<T>(this IEnumerable<T> source)
+			where T : IComparable<T>
+			=> source.OrderByDescending(ReturnSelf);
+
 		/// <inheritdoc cref="List{T}.RemoveAll"/>
 		/// <remarks>
 		/// (This is an extension method which reimplements <see cref="List{T}.RemoveAll"/> for other <see cref="ICollection{T}">collections</see>.
@@ -180,6 +191,10 @@ namespace BizHawk.Common.CollectionExtensions
 			return c - list.Count;
 		}
 
+		[MethodImpl(MethodImplOptions.AggressiveInlining)]
+		private static T ReturnSelf<T>(this T self)
+			=> self;
+
 		public static bool IsSortedAsc<T>(this IReadOnlyList<T> list)
 			where T : IComparable<T>
 		{

src/BizHawk.Emulation.Common/VSystemID.cs

@@ -2,6 +2,8 @@ using System.Collections.Generic;
 using System.Linq;
 using System.Reflection;
 
+using BizHawk.Common.CollectionExtensions;
+
 namespace BizHawk.Emulation.Common
 {
 	/// <summary>
@@ -74,8 +76,7 @@ namespace BizHawk.Emulation.Common
 		private static List<string> AllSysIDs
 			=> _allSysIDs ??= typeof(Raw).GetFields(BindingFlags.Public | BindingFlags.Static)
 				.Select(x => (string) x.GetRawConstantValue())
-				.OrderBy(s => s)
-				.ToList();
+				.Order().ToList();
 
 		/// <returns><paramref name="sysID"/> iff it's in <see cref="Raw">the valid list</see>, else <see langword="null"/></returns>
 		public static string? Validate(string sysID)