Fix completion to show both property and extension method with same name

src/EditorFeatures/CSharpTest/Completion/CompletionProviders/SymbolCompletionProviderTests.cs

@@ -14333,4 +14333,43 @@ class Foo2 { }
             }
             """, commitChar: commitChar, sourceCodeKind: SourceCodeKind.Regular);
     }
+
+    [Fact, WorkItem("https://github.com/dotnet/roslyn/issues/78766")]
+    public async Task ExtensionMethodAndPropertyWithSameName()
+    {
+        var markup = """
+            using NS1;
+
+            var x = new MyClass();
+            x.$$
+
+            namespace NS1
+            {
+                public class MyClass
+                {
+                    public int MyMember { get; set; }
+                }
+
+                public static class Extensions
+                {
+                    public static MyClass MyMember(this MyClass c)
+                        => c;
+                }
+            }
+            """;
+
+        MarkupTestFile.GetPosition(markup, out var code, out int position);
+
+        using var workspace = EditorTestWorkspace.CreateCSharp(code);
+        var document = workspace.CurrentSolution.Projects.First().Documents.First();
+
+        var service = GetCompletionService(document.Project);
+        var completionList = await GetCompletionListAsync(service, document, position, Microsoft.CodeAnalysis.Completion.CompletionTrigger.Invoke);
+
+        var myMemberItems = completionList.ItemsList.Where(item => item.DisplayText == "MyMember").ToList();
+
+        // We should have two separate completion items for MyMember:
+        // one for the property and one for the extension method
+        Assert.Equal(2, myMemberItems.Count);
+    }
 }

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

@@ -158,17 +158,21 @@ private ImmutableArray<CompletionItem> CreateItems(
         // Use SymbolReferenceEquivalenceComparer.Instance as the value comparer as we
         // don't want symbols with just the same name to necessarily match
         // (as the default comparer on SymbolAndSelectionInfo does)
-        var symbolGroups = new MultiDictionary<(string displayText, string suffix, string insertionText), SymbolAndSelectionInfo>(
+        //
+        // Include whether the symbol is a method in the key to avoid merging methods with non-methods
+        // that have the same name (e.g., a property and an extension method with the same name).
+        // https://github.com/dotnet/roslyn/issues/78766
+        var symbolGroups = new MultiDictionary<(string displayText, string suffix, string insertionText, bool isMethod), SymbolAndSelectionInfo>(
             capacity: symbols.Length,
-            comparer: EqualityComparer<(string, string, string)>.Default,
+            comparer: EqualityComparer<(string, string, string, bool)>.Default,
             valueComparer: SymbolReferenceEquivalenceComparer.Instance);
 
         foreach (var symbol in symbols)
         {
             var texts = GetDisplayAndSuffixAndInsertionText(symbol.Symbol, contextLookup(symbol));
             if (!string.IsNullOrWhiteSpace(texts.displayText))
             {
-                symbolGroups.Add(texts, symbol);
+                symbolGroups.Add((texts.displayText, texts.suffix, texts.insertionText, symbol.Symbol.Kind == SymbolKind.Method), symbol);
             }
         }