Small optimization around ProjectState modification operations

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

@@ -765,6 +765,9 @@ public AnalyzerReference GetAnalyzerReferenceForGenerator(ISourceGenerator gener
 
     public ProjectState AddDocuments(ImmutableArray<DocumentState> documents)
     {
+        if (documents.IsEmpty)
+            return this;
+
         Debug.Assert(!documents.Any(d => DocumentStates.Contains(d.Id)));
 
         return With(
@@ -774,6 +777,9 @@ public ProjectState AddDocuments(ImmutableArray<DocumentState> documents)
 
     public ProjectState AddAdditionalDocuments(ImmutableArray<AdditionalDocumentState> documents)
     {
+        if (documents.IsEmpty)
+            return this;
+
         Debug.Assert(!documents.Any(d => AdditionalDocumentStates.Contains(d.Id)));
 
         return With(
@@ -783,6 +789,9 @@ public ProjectState AddAdditionalDocuments(ImmutableArray<AdditionalDocumentStat
 
     public ProjectState AddAnalyzerConfigDocuments(ImmutableArray<AnalyzerConfigDocumentState> documents)
     {
+        if (documents.IsEmpty)
+            return this;
+
         Debug.Assert(!documents.Any(d => AnalyzerConfigDocumentStates.Contains(d.Id)));
 
         var newAnalyzerConfigDocumentStates = AnalyzerConfigDocumentStates.AddRange(documents);
@@ -811,6 +820,9 @@ private ProjectState CreateNewStateForChangedAnalyzerConfigDocuments(TextDocumen
 
     public ProjectState RemoveDocuments(ImmutableArray<DocumentId> documentIds)
     {
+        if (documentIds.IsEmpty)
+            return this;
+
         // We create a new CachingAnalyzerConfigSet for the new snapshot to avoid holding onto cached information
         // for removed documents.
         return With(
@@ -821,20 +833,29 @@ public ProjectState RemoveDocuments(ImmutableArray<DocumentId> documentIds)
 
     public ProjectState RemoveAdditionalDocuments(ImmutableArray<DocumentId> documentIds)
     {
+        if (documentIds.IsEmpty)
+            return this;
+
         return With(
             projectInfo: ProjectInfo.WithVersion(Version.GetNewerVersion()),
             additionalDocumentStates: AdditionalDocumentStates.RemoveRange(documentIds));
     }
 
     public ProjectState RemoveAnalyzerConfigDocuments(ImmutableArray<DocumentId> documentIds)
     {
+        if (documentIds.IsEmpty)
+            return this;
+
         var newAnalyzerConfigDocumentStates = AnalyzerConfigDocumentStates.RemoveRange(documentIds);
 
         return CreateNewStateForChangedAnalyzerConfigDocuments(newAnalyzerConfigDocumentStates);
     }
 
-    public ProjectState RemoveAllDocuments()
+    public ProjectState RemoveAllNormalDocuments()
     {
+        if (DocumentStates.IsEmpty)
+            return this;
+
         // We create a new CachingAnalyzerConfigSet for the new snapshot to avoid holding onto cached information
         // for removed documents.
         return With(

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

@@ -311,7 +311,7 @@ InProgressState BuildInProgressStateFromNoCompilationState()
                         // other.  It also means that if we're in the process of parsing documents in that chain, that
                         // we'll see the results of how far we've gotten if someone asks for a frozen snapshot midway
                         // through.
-                        var initialProjectState = this.ProjectState.RemoveAllDocuments();
+                        var initialProjectState = this.ProjectState.RemoveAllNormalDocuments();
                         var initialCompilation = this.CreateEmptyCompilation();
 
                         var translationActionsBuilder = ImmutableList.CreateBuilder<TranslationAction>();
@@ -723,7 +723,7 @@ public ICompilationTracker FreezePartialState(CancellationToken cancellationToke
 
                     // Transition us to a state that only has documents for the files we've already parsed.
                     var frozenProjectState = this.ProjectState
-                        .RemoveAllDocuments()
+                        .RemoveAllNormalDocuments()
                         .AddDocuments(documentsWithTreesBuilder.ToImmutableAndClear());
 
                     // Defer creating these compilations.  It's common to freeze projects (as part of a solution freeze)