Remove ImmutableHashMap in favor of ImmutableDictionary (#72520)

My understanding is that ImmutableHashMap precedes ImmutableDictionary and only exists because of that reason. These two data structures appear to have similar performance and functionality. There is no reason to have our own implementation if there isn't an advantage to doing so.

src/Workspaces/Core/Portable/Workspace/Solution/Project.cs

@@ -15,7 +15,6 @@
 using Microsoft.CodeAnalysis.Host;
 using Microsoft.CodeAnalysis.Shared.Extensions;
 using Microsoft.CodeAnalysis.Text;
-using Roslyn.Collections.Immutable;
 using Roslyn.Utilities;
 
 namespace Microsoft.CodeAnalysis;
@@ -28,10 +27,10 @@ public partial class Project
 {
     private readonly Solution _solution;
     private readonly ProjectState _projectState;
-    private ImmutableHashMap<DocumentId, Document> _idToDocumentMap = [];
-    private ImmutableHashMap<DocumentId, SourceGeneratedDocument> _idToSourceGeneratedDocumentMap = [];
-    private ImmutableHashMap<DocumentId, AdditionalDocument> _idToAdditionalDocumentMap = [];
-    private ImmutableHashMap<DocumentId, AnalyzerConfigDocument> _idToAnalyzerConfigDocumentMap = [];
+    private ImmutableDictionary<DocumentId, Document?> _idToDocumentMap = ImmutableDictionary<DocumentId, Document?>.Empty;
+    private ImmutableDictionary<DocumentId, SourceGeneratedDocument> _idToSourceGeneratedDocumentMap = ImmutableDictionary<DocumentId, SourceGeneratedDocument>.Empty;
+    private ImmutableDictionary<DocumentId, AdditionalDocument?> _idToAdditionalDocumentMap = ImmutableDictionary<DocumentId, AdditionalDocument?>.Empty;
+    private ImmutableDictionary<DocumentId, AnalyzerConfigDocument?> _idToAnalyzerConfigDocumentMap = ImmutableDictionary<DocumentId, AnalyzerConfigDocument?>.Empty;
 
     internal Project(Solution solution, ProjectState projectState)
     {
@@ -236,19 +235,19 @@ public bool ContainsAnalyzerConfigDocument(DocumentId documentId)
     /// Get the document in this project with the specified document Id.
     /// </summary>
     public Document? GetDocument(DocumentId documentId)
-        => ImmutableHashMapExtensions.GetOrAdd(ref _idToDocumentMap, documentId, s_tryCreateDocumentFunction, this);
+        => ImmutableInterlocked.GetOrAdd(ref _idToDocumentMap, documentId, s_tryCreateDocumentFunction, this);
 
     /// <summary>
     /// Get the additional document in this project with the specified document Id.
     /// </summary>
     public TextDocument? GetAdditionalDocument(DocumentId documentId)
-        => ImmutableHashMapExtensions.GetOrAdd(ref _idToAdditionalDocumentMap, documentId, s_tryCreateAdditionalDocumentFunction, this);
+        => ImmutableInterlocked.GetOrAdd(ref _idToAdditionalDocumentMap, documentId, s_tryCreateAdditionalDocumentFunction, this);
 
     /// <summary>
     /// Get the analyzer config document in this project with the specified document Id.
     /// </summary>
     public AnalyzerConfigDocument? GetAnalyzerConfigDocument(DocumentId documentId)
-        => ImmutableHashMapExtensions.GetOrAdd(ref _idToAnalyzerConfigDocumentMap, documentId, s_tryCreateAnalyzerConfigDocumentFunction, this);
+        => ImmutableInterlocked.GetOrAdd(ref _idToAnalyzerConfigDocumentMap, documentId, s_tryCreateAnalyzerConfigDocumentFunction, this);
 
     /// <summary>
     /// Gets a document or a source generated document in this solution with the specified document ID.
@@ -285,7 +284,7 @@ public async ValueTask<IEnumerable<SourceGeneratedDocument>> GetSourceGeneratedD
 
         // return an iterator to avoid eagerly allocating all the document instances
         return generatedDocumentStates.States.Values.Select(state =>
-            ImmutableHashMapExtensions.GetOrAdd(ref _idToSourceGeneratedDocumentMap, state.Id, s_createSourceGeneratedDocumentFunction, (state, this)))!;
+            ImmutableInterlocked.GetOrAdd(ref _idToSourceGeneratedDocumentMap, state.Id, s_createSourceGeneratedDocumentFunction, (state, this)));
     }
 
     internal async ValueTask<IEnumerable<Document>> GetAllRegularAndSourceGeneratedDocumentsAsync(CancellationToken cancellationToken = default)
@@ -318,7 +317,7 @@ internal async ValueTask<IEnumerable<Document>> GetAllRegularAndSourceGeneratedD
     }
 
     internal SourceGeneratedDocument GetOrCreateSourceGeneratedDocument(SourceGeneratedDocumentState state)
-        => ImmutableHashMapExtensions.GetOrAdd(ref _idToSourceGeneratedDocumentMap, state.Id, s_createSourceGeneratedDocumentFunction, (state, this))!;
+        => ImmutableInterlocked.GetOrAdd(ref _idToSourceGeneratedDocumentMap, state.Id, s_createSourceGeneratedDocumentFunction, (state, this));
 
     /// <summary>
     /// Returns the <see cref="SourceGeneratedDocumentState"/> for a source generated document that has already been generated and observed.
@@ -349,7 +348,7 @@ internal SourceGeneratedDocument GetOrCreateSourceGeneratedDocument(SourceGenera
         if (documentState == null)
             return null;
 
-        return ImmutableHashMapExtensions.GetOrAdd(ref _idToSourceGeneratedDocumentMap, documentId, s_createSourceGeneratedDocumentFunction, (documentState, this));
+        return ImmutableInterlocked.GetOrAdd(ref _idToSourceGeneratedDocumentMap, documentId, s_createSourceGeneratedDocumentFunction, (documentState, this));
     }
 
     internal ValueTask<ImmutableArray<Diagnostic>> GetSourceGeneratorDiagnosticsAsync(CancellationToken cancellationToken)

src/Workspaces/Core/Portable/Workspace/Solution/Solution.cs

@@ -15,7 +15,6 @@
 using Microsoft.CodeAnalysis.Options;
 using Microsoft.CodeAnalysis.Shared.Extensions;
 using Microsoft.CodeAnalysis.Text;
-using Roslyn.Collections.Immutable;
 using Roslyn.Utilities;
 
 namespace Microsoft.CodeAnalysis;
@@ -28,7 +27,7 @@ public partial class Solution
     private readonly SolutionCompilationState _compilationState;
 
     // Values for all these are created on demand.
-    private ImmutableHashMap<ProjectId, Project> _projectIdToProjectMap;
+    private ImmutableDictionary<ProjectId, Project> _projectIdToProjectMap;
 
     /// <summary>
     /// Result of calling <see cref="WithFrozenPartialCompilationsAsync"/>.
@@ -45,7 +44,7 @@ private Solution(
         SolutionCompilationState compilationState,
         AsyncLazy<Solution>? cachedFrozenSolution = null)
     {
-        _projectIdToProjectMap = [];
+        _projectIdToProjectMap = ImmutableDictionary<ProjectId, Project>.Empty;
         _compilationState = compilationState;
 
         _cachedFrozenSolution = cachedFrozenSolution ??
@@ -141,7 +140,7 @@ public Workspace Workspace
     {
         if (this.ContainsProject(projectId))
         {
-            return ImmutableHashMapExtensions.GetOrAdd(ref _projectIdToProjectMap, projectId, s_createProjectFunction, this);
+            return ImmutableInterlocked.GetOrAdd(ref _projectIdToProjectMap, projectId, s_createProjectFunction, this);
         }
 
         return null;

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

@@ -540,8 +540,6 @@
     <Compile Include="$(MSBuildThisFileDirectory)Extensions\TextSpanExtensions.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Utilities\CompilerUtilities\CompilerPathUtilities.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Utilities\CompilerUtilities\ImmutableDictionaryExtensions.cs" />
-    <Compile Include="$(MSBuildThisFileDirectory)Utilities\CompilerUtilities\ImmutableHashMap.cs" />
-    <Compile Include="$(MSBuildThisFileDirectory)Utilities\CompilerUtilities\ImmutableHashMapExtensions.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Utilities\ConcatImmutableArray`1.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Utilities\ReferenceCountedDisposable.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Utilities\ReferenceCountedDisposableCache.cs" />