Adds EqualityComparer<T>.Create polyfill

src/Dependencies/Contracts/EqualityComparerExtensions.cs

@@ -0,0 +1,63 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+#nullable enable
+
+#if !NET8_0_OR_GREATER
+using System.Diagnostics.CodeAnalysis;
+#endif
+
+namespace System.Collections.Generic;
+
+internal static class RoslynEqualityComparerExtensions
+{
+#if NET8_0_OR_GREATER
+
+    // for binary compatibility
+    public static EqualityComparer<T> Create<T>(Func<T?, T?, bool> equals, Func<T, int>? getHashCode = null)
+        => EqualityComparer<T>.Create(equals, getHashCode);
+
+#else
+    // Implementation based on https://github.com/dotnet/runtime/blob/main/src/libraries/System.Private.CoreLib/src/System/Collections/Generic/EqualityComparer.cs
+
+    extension<T>(EqualityComparer<T>)
+    {
+        /// <summary>
+        /// Creates an <see cref="EqualityComparer{T}"/> by using the specified delegates as the implementation of the comparer's
+        /// <see cref="EqualityComparer{T}.Equals"/> and <see cref="EqualityComparer{T}.GetHashCode"/> methods.
+        /// </summary>
+        /// <param name="equals">The delegate to use to implement the <see cref="EqualityComparer{T}.Equals"/> method.</param>
+        /// <param name="getHashCode">
+        /// The delegate to use to implement the <see cref="EqualityComparer{T}.GetHashCode"/> method.
+        /// If no delegate is supplied, calls to the resulting comparer's <see cref="EqualityComparer{T}.GetHashCode"/>
+        /// will throw <see cref="NotSupportedException"/>.
+        /// </param>
+        /// <returns>The new comparer.</returns>
+        public static EqualityComparer<T> Create(Func<T?, T?, bool> equals, Func<T, int>? getHashCode = null)
+        {
+            getHashCode ??= _ => throw new NotSupportedException();
+            return new DelegateEqualityComparer<T>(equals, getHashCode);
+        }
+    }
+
+    private sealed class DelegateEqualityComparer<T>(Func<T?, T?, bool> equals, Func<T, int> getHashCode) : EqualityComparer<T>
+    {
+        private readonly Func<T?, T?, bool> _equals = equals;
+        private readonly Func<T, int> _getHashCode = getHashCode;
+
+        public override bool Equals(T? x, T? y) =>
+            _equals(x, y);
+
+        public override int GetHashCode(T obj) =>
+            _getHashCode(obj);
+
+        public override bool Equals(object? obj)
+            => obj is DelegateEqualityComparer<T> other && _equals == other._equals && _getHashCode == other._getHashCode;
+
+        public override int GetHashCode()
+            => unchecked(_equals.GetHashCode() * (int)0xA5555529 + _getHashCode.GetHashCode());
+    }
+#endif
+}
+

src/Dependencies/Contracts/Microsoft.CodeAnalysis.Contracts.projitems

@@ -25,6 +25,8 @@
     <Compile Include="$(MSBuildThisFileDirectory)RequiredMemberAttribute.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)SetsRequiredMembersAttribute.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)ExceptionUtilities.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)EqualityComparerExtensions.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)ReferenceEqualityComparer.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Index.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Range.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)ErrorReporting\FatalError.cs" />

src/Compilers/Core/Portable/InternalUtilities/ReferenceEqualityComparer.cs → src/Dependencies/Contracts/ReferenceEqualityComparer.cs

@@ -4,7 +4,9 @@
 
 using System.Runtime.CompilerServices;
 
-#if NET5_0_OR_GREATER
+#nullable enable
+
+#if NET
 
 #pragma warning disable RS0016 // Add public types and members to the declared API (this is a supporting forwarder for an internal polyfill API)
 [assembly: TypeForwardedTo(typeof(System.Collections.Generic.ReferenceEqualityComparer))]

src/EditorFeatures/Test/Collections/Immutable/Maps/MapTests.cs

@@ -82,7 +82,9 @@ public void TestRemove()
     [Fact]
     public void TestPathology()
     {
-        var map = ImmutableDictionary.Create<string, int>(new PathologicalComparer<string>())
+        var comparer = EqualityComparer<string>.Create(EqualityComparer<string>.Default.Equals, _ => 0);
+
+        var map = ImmutableDictionary.Create<string, int>(comparer)
             .Add("1", 1)
             .Add("2", 2)
             .Add("3", 3)
@@ -118,13 +120,4 @@ public void TestPathology()
         map = map.Remove("5");
         Assert.Empty(map);
     }
-
-    private sealed class PathologicalComparer<T> : IEqualityComparer<T>
-    {
-        public bool Equals(T x, T y)
-            => EqualityComparer<T>.Default.Equals(x, y);
-
-        public int GetHashCode(T obj)
-            => 0;
-    }
 }

src/Features/Core/Portable/Completion/Providers/AbstractKeywordCompletionProvider.cs

@@ -19,7 +19,9 @@ namespace Microsoft.CodeAnalysis.Completion.Providers;
 internal abstract partial class AbstractKeywordCompletionProvider<TContext> : LSPCompletionProvider
     where TContext : SyntaxContext
 {
-    private static readonly Comparer s_comparer = new();
+    private static readonly EqualityComparer<CompletionItem> s_comparer = EqualityComparer<CompletionItem>.Create(
+        static (x, y) => x?.DisplayText == y?.DisplayText,
+        static x => x.DisplayText.GetHashCode());
 
     private readonly ImmutableArray<IKeywordRecommender<TContext>> _keywordRecommenders;
 
@@ -72,13 +74,4 @@ private async Task<ImmutableArray<RecommendedKeyword>> RecommendKeywordsAsync(
 
     public sealed override Task<TextChange?> GetTextChangeAsync(Document document, CompletionItem item, char? ch, CancellationToken cancellationToken)
         => Task.FromResult((TextChange?)new TextChange(item.Span, item.DisplayText));
-
-    private sealed class Comparer : IEqualityComparer<CompletionItem>
-    {
-        public bool Equals(CompletionItem? x, CompletionItem? y)
-            => x?.DisplayText == y?.DisplayText;
-
-        public int GetHashCode(CompletionItem obj)
-            => Hash.Combine(obj.DisplayText.GetHashCode(), obj.DisplayText.GetHashCode());
-    }
 }

src/Workspaces/SharedUtilitiesAndExtensions/Compiler/Core/CompilerExtensions.projitems

@@ -1,4 +1,4 @@
-<?xml version="1.0" encoding="utf-8"?>
+<?xml version="1.0" encoding="utf-8"?>
 <Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
   <PropertyGroup>
     <MSBuildAllProjects>$(MSBuildAllProjects);$(MSBuildThisFileFullPath)</MSBuildAllProjects>
@@ -19,7 +19,6 @@
     <Compile Include="$(MSBuildThisFileDirectory)..\..\..\..\Compilers\Core\Portable\InternalUtilities\RoslynExperiments.cs" Link="InternalUtilities\RoslynExperiments.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)..\..\..\..\Compilers\Core\Portable\InternalUtilities\InterlockedOperations.cs" Link="InternalUtilities\InterlockedOperations.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)..\..\..\..\Compilers\Core\Portable\InternalUtilities\ReadOnlyMemoryOfCharComparer.cs" Link="InternalUtilities\ReadOnlyMemoryOfCharComparer.cs" />
-    <Compile Include="$(MSBuildThisFileDirectory)..\..\..\..\Compilers\Core\Portable\InternalUtilities\ReferenceEqualityComparer.cs" Link="InternalUtilities\ReferenceEqualityComparer.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)..\..\..\..\Compilers\Core\Portable\InternalUtilities\SingleInitNullable.cs" Link="InternalUtilities\SingleInitNullable.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)..\..\..\..\Compilers\Core\Portable\InternalUtilities\SharedStopwatch.cs" Link="InternalUtilities\SharedStopwatch.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)..\..\..\..\Compilers\Core\Portable\InternalUtilities\ValueTaskFactory.cs" Link="InternalUtilities\ValueTaskFactory.cs" />