Switch off of mutlidictionary

src/VisualStudio/Core/Impl/SolutionExplorer/SymbolTree/RootSymbolTreeItemSourceProvider.cs

@@ -3,11 +3,11 @@
 // See the LICENSE file in the project root for more information.
 
 using System;
+using System.Collections.Generic;
 using System.ComponentModel;
 using System.ComponentModel.Composition;
 using System.Threading;
 using System.Threading.Tasks;
-using ICSharpCode.Decompiler.Util;
 using Microsoft.CodeAnalysis;
 using Microsoft.CodeAnalysis.Collections;
 using Microsoft.CodeAnalysis.Editor.Shared.Utilities;
@@ -44,7 +44,7 @@ internal sealed partial class RootSymbolTreeItemSourceProvider : AttachedCollect
     /// of that file through that project.
     /// </summary>
     /// <remarks>Lock this instance when reading/writing as it is used over different threads.</remarks>
-    private readonly MultiDictionary<string, RootSymbolTreeItemCollectionSource> _filePathToCollectionSources = new(
+    private readonly Dictionary<string, List<RootSymbolTreeItemCollectionSource>> _filePathToCollectionSources = new(
         StringComparer.OrdinalIgnoreCase);
 
     /// <summary>
@@ -166,7 +166,9 @@ await source.UpdateIfEverExpandedAsync(cancellationToken)
 
         var source = new RootSymbolTreeItemCollectionSource(this, item);
         lock (_filePathToCollectionSources)
-            _filePathToCollectionSources.Add(currentFilePath, source);
+        {
+            AddToDictionary(currentFilePath, source);
+        }
 
         // Register to hear about if this hierarchy is disposed. We'll stop watching it if so.
         item.PropertyChanged += OnItemPropertyChanged;
@@ -181,7 +183,7 @@ void OnItemPropertyChanged(object sender, PropertyChangedEventArgs e)
                 // event for the IsDisposed property. When this fires, we remove the filePath->sourcce mapping we're holding.
                 lock (_filePathToCollectionSources)
                 {
-                    _filePathToCollectionSources.Remove(currentFilePath, source);
+                    RemoveFromDictionary(currentFilePath, source);
                 }
 
                 item.PropertyChanged -= OnItemPropertyChanged;
@@ -195,8 +197,8 @@ void OnItemPropertyChanged(object sender, PropertyChangedEventArgs e)
                     {
 
                         // Unlink the oldPath->source mapping, and add a new line for the newPath->source.
-                        _filePathToCollectionSources.Remove(currentFilePath, source);
-                        _filePathToCollectionSources.Add(newPath, source);
+                        RemoveFromDictionary(currentFilePath, source);
+                        AddToDictionary(newPath, source);
 
                         // Keep track of the 'newPath'.
                         currentFilePath = newPath;
@@ -211,5 +213,29 @@ void OnItemPropertyChanged(object sender, PropertyChangedEventArgs e)
                 }
             }
         }
+
+        void AddToDictionary(string currentFilePath, RootSymbolTreeItemCollectionSource source)
+        {
+            if (!_filePathToCollectionSources.TryGetValue(currentFilePath, out var sources))
+            {
+                sources = [];
+                _filePathToCollectionSources[currentFilePath] = sources;
+            }
+
+            sources.Add(source);
+        }
+
+        void RemoveFromDictionary(string currentFilePath, RootSymbolTreeItemCollectionSource source)
+        {
+            if (_filePathToCollectionSources.TryGetValue(currentFilePath, out var sources))
+            {
+                sources.Remove(source);
+
+                if (sources.Count == 0)
+                {
+                    _filePathToCollectionSources.Remove(currentFilePath);
+                }
+            }
+        }
     }
 }