Completion does not work in the Immediate Window after expression eva…

…luation (#33875)

src/VisualStudio/Core/Def/Implementation/DebuggerIntelliSense/DebuggerIntellisenseFilter.cs

@@ -1,6 +1,7 @@
 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
 using System;
+using System.Diagnostics;
 using System.Runtime.InteropServices;
 using Microsoft.CodeAnalysis.Editor;
 using Microsoft.CodeAnalysis.Editor.Shared.Extensions;
@@ -180,29 +181,25 @@ protected override ITextView ConvertTextView()
 
         internal void SetContext(AbstractDebuggerIntelliSenseContext context)
         {
-            // We're never notified of being disabled in the immediate window, so the
-            // best we can do is only keep resources from one context alive at a time.
-            Dispose();
-
+            // If there was an old context, it must be cleaned before calling SetContext.
+            Debug.Assert(_context == null);
             _context = context;
             this.SetCommandHandlers(context.Buffer);
         }
 
         internal void RemoveContext()
         {
-            Dispose();
-            _context = null;
+            if (_context != null)
+            {
+                _context.Dispose();
+                _context = null;
+            }
         }
 
         internal void SetContentType(bool install)
             => _context?.SetContentType(install);
 
         public void Dispose()
-        {
-            if (_context != null)
-            {
-                _context.Dispose();
-            }
-        }
+            => RemoveContext();
     }
 }

src/VisualStudio/Core/Def/Implementation/LanguageService/AbstractLanguageService`2.IVsImmediateStatementCompletion2.cs

@@ -92,15 +92,15 @@ int IVsImmediateStatementCompletion2.InstallStatementCompletion(int install, IVs
                     return VSConstants.E_FAIL;
                 }
 
+                // Clean the old context in any case upfront: 
+                // even if we fail to initialize, the old context must be cleaned.
+                this.filters[textView].RemoveContext();
+
                 var context = CreateContext(view, textView, debuggerBuffer, contextBuffer, currentStatementSpan);
                 if (context.TryInitialize())
                 {
                     this.filters[textView].SetContext(context);
                 }
-                else
-                {
-                    this.filters[textView].RemoveContext();
-                }
             }
 
             return VSConstants.S_OK;