Simplify the mechnanism for all languages to extend how we cascade between symbols

src/Workspaces/Core/Portable/FindSymbols/FindReferences/FindReferencesSearchEngine_MapCreation.cs

@@ -165,16 +165,23 @@ private async Task DetermineAllSymbolsCoreAsync(ISymbol symbol, ConcurrentSet<IS
                 {
                     finderTasks.Add(Task.Run(async () =>
                     {
-                        var symbols = await f.DetermineCascadedSymbolsAsync(searchSymbol, _solution, projects, _cancellationToken).ConfigureAwait(false) ?? SpecializedCollections.EmptyEnumerable<ISymbol>();
+                        var symbolTasks = new List<Task>();
 
-                        _cancellationToken.ThrowIfCancellationRequested();
+                        var symbols = await f.DetermineCascadedSymbolsAsync(searchSymbol, _solution, projects, _cancellationToken).ConfigureAwait(false);
+                        AddSymbolTasks(result, symbols, symbolTasks);
 
-                        List<Task> symbolTasks = new List<Task>();
-                        foreach (var child in symbols)
+                        // Defer to the language to see if it wants to cascade here in some special way.
+                        var symbolProject = _solution.GetProject(searchSymbol.ContainingAssembly);
+                        if (symbolProject != null)
                         {
-                            symbolTasks.Add(Task.Run(async () => await DetermineAllSymbolsCoreAsync(child, result).ConfigureAwait(false), _cancellationToken));
+                            var service = symbolProject.LanguageServices.GetService<ILanguageServiceReferenceFinder>();
+                            symbols = await service.DetermineCascadedSymbolsAsync(searchSymbol, symbolProject, _cancellationToken).ConfigureAwait(false);
+                            AddSymbolTasks(result, symbols, symbolTasks);
                         }
 
+                        _cancellationToken.ThrowIfCancellationRequested();
+
+
                         await Task.WhenAll(symbolTasks).ConfigureAwait(false);
                     }, _cancellationToken));
                 }
@@ -183,6 +190,18 @@ private async Task DetermineAllSymbolsCoreAsync(ISymbol symbol, ConcurrentSet<IS
             }
         }
 
+        private void AddSymbolTasks(ConcurrentSet<ISymbol> result, IEnumerable<ISymbol> symbols, List<Task> symbolTasks)
+        {
+            if (symbols != null)
+            {
+                foreach (var child in symbols)
+                {
+                    _cancellationToken.ThrowIfCancellationRequested();
+                    symbolTasks.Add(Task.Run(async () => await DetermineAllSymbolsCoreAsync(child, result).ConfigureAwait(false), _cancellationToken));
+                }
+            }
+        }
+
         private ImmutableHashSet<Project> GetProjectScope()
         {
             if (_documents == null)

src/Workspaces/Core/Portable/FindSymbols/FindReferences/Finders/ILanguageServiceReferenceFinder.cs

@@ -9,7 +9,6 @@ namespace Microsoft.CodeAnalysis.FindSymbols.Finders
 {
     internal interface ILanguageServiceReferenceFinder : ILanguageService
     {
-        Task<IEnumerable<ISymbol>> DetermineCascadedSymbolsAsync(INamedTypeSymbol namedType, Project project, CancellationToken cancellationToken);
-        Task<IEnumerable<ISymbol>> DetermineCascadedSymbolsAsync(IPropertySymbol property, Project project, CancellationToken cancellationToken);
+        Task<IEnumerable<ISymbol>> DetermineCascadedSymbolsAsync(ISymbol symbol, Project project, CancellationToken cancellationToken);
     }
 }
\ No newline at end of file

src/Workspaces/Core/Portable/FindSymbols/FindReferences/Finders/NamedTypeSymbolReferenceFinder.cs

@@ -20,14 +20,13 @@ protected override bool CanFind(INamedTypeSymbol symbol)
             return symbol.TypeKind != TypeKind.Error;
         }
 
-        protected override async Task<IEnumerable<ISymbol>> DetermineCascadedSymbolsAsync(
+        protected override Task<IEnumerable<ISymbol>> DetermineCascadedSymbolsAsync(
             INamedTypeSymbol symbol,
             Solution solution,
             IImmutableSet<Project> projects,
             CancellationToken cancellationToken)
         {
             List<ISymbol> result = null;
-
             if (symbol.AssociatedSymbol != null)
             {
                 result = Add(result, SpecializedCollections.SingletonEnumerable(symbol.AssociatedSymbol));
@@ -39,24 +38,7 @@ protected override bool CanFind(INamedTypeSymbol symbol)
             // cascade to destructor
             result = Add(result, symbol.GetMembers(WellKnownMemberNames.DestructorName));
 
-            result = Add(result, await DetermineLanguageCascadedSymbolsAsync(symbol, solution, cancellationToken).ConfigureAwait(false));
-
-            return result ?? SpecializedCollections.EmptyList<ISymbol>();
-        }
-
-        private async Task<IEnumerable<ISymbol>> DetermineLanguageCascadedSymbolsAsync(INamedTypeSymbol symbol, Solution solution, CancellationToken cancellationToken)
-        {
-            var definitionProject = solution.GetProject(symbol.ContainingAssembly, cancellationToken);
-            if (definitionProject != null)
-            {
-                var referenceFinder = definitionProject.LanguageServices.GetService<ILanguageServiceReferenceFinder>();
-                if (referenceFinder != null)
-                {
-                    return await referenceFinder.DetermineCascadedSymbolsAsync(symbol, definitionProject, cancellationToken).ConfigureAwait(false);
-                }
-            }
-
-            return null;
+            return Task.FromResult<IEnumerable<ISymbol>>(result ?? SpecializedCollections.EmptyList<ISymbol>());
         }
 
         private List<ISymbol> Add(List<ISymbol> result, IEnumerable<ISymbol> enumerable)

src/Workspaces/Core/Portable/FindSymbols/FindReferences/Finders/PropertySymbolReferenceFinder.cs

@@ -38,17 +38,6 @@ protected override bool CanFind(IPropertySymbol symbol)
                 result = result.Concat(symbol.SetMethod);
             }
 
-            var project = solution.GetProject(symbol.ContainingAssembly, cancellationToken);
-            var service = project?.LanguageServices.GetService<ILanguageServiceReferenceFinder>();
-            if (service != null)
-            {
-                var languageCascades = await service.DetermineCascadedSymbolsAsync(symbol, project, cancellationToken).ConfigureAwait(false);
-                if (languageCascades != null)
-                {
-                    result = result.Concat(languageCascades);
-                }
-            }
-
             return result;
         }
 

src/Workspaces/VisualBasic/Portable/FindSymbols/VisualBasicReferenceFinder.vb

@@ -12,7 +12,17 @@ Namespace Microsoft.CodeAnalysis.FindSymbols
     Friend Class VisualBasicReferenceFinder
         Implements ILanguageServiceReferenceFinder
 
-        Public Async Function DetermineCascadedSymbolsAsync([property] As IPropertySymbol, project As Project, cancellationToken As CancellationToken) As Task(Of IEnumerable(Of ISymbol)) Implements ILanguageServiceReferenceFinder.DetermineCascadedSymbolsAsync
+        Public Function DetermineCascadedSymbolsAsync(symbol As ISymbol, project As Project, cancellationToken As CancellationToken) As Task(Of IEnumerable(Of ISymbol)) Implements ILanguageServiceReferenceFinder.DetermineCascadedSymbolsAsync
+            If symbol.Kind = SymbolKind.Property Then
+                Return DetermineCascadedSymbolsAsync(DirectCast(symbol, IPropertySymbol), project, cancellationToken)
+            ElseIf symbol.Kind = SymbolKind.NamedType Then
+                Return DetermineCascadedSymbolsAsync(DirectCast(symbol, INamedTypeSymbol), project, cancellationToken)
+            Else
+                Return Nothing
+            End If
+        End Function
+
+        Private Async Function DetermineCascadedSymbolsAsync([property] As IPropertySymbol, project As Project, cancellationToken As CancellationToken) As Task(Of IEnumerable(Of ISymbol))
             Dim compilation = Await project.GetCompilationAsync(cancellationToken).ConfigureAwait(False)
             Dim relatedSymbol = [property].FindRelatedExplicitlyDeclaredSymbol(compilation)
 
@@ -21,7 +31,7 @@ Namespace Microsoft.CodeAnalysis.FindSymbols
                 SpecializedCollections.SingletonEnumerable(relatedSymbol))
         End Function
 
-        Public Async Function DetermineCascadedSymbolsAsync(namedType As INamedTypeSymbol, project As Project, cancellationToken As CancellationToken) As Task(Of IEnumerable(Of ISymbol)) Implements ILanguageServiceReferenceFinder.DetermineCascadedSymbolsAsync
+        Private Async Function DetermineCascadedSymbolsAsync(namedType As INamedTypeSymbol, project As Project, cancellationToken As CancellationToken) As Task(Of IEnumerable(Of ISymbol))
             Dim compilation = Await project.GetCompilationAsync(cancellationToken).ConfigureAwait(False)
 
             ' If this is a WinForms project, then the VB 'my' feature may have synthesized