Make abstract

src/Features/CSharp/Portable/Completion/CompletionProviders/TupleNameCompletionProvider.cs

@@ -118,5 +118,7 @@ private void AddItems(ImmutableArray<INamedTypeSymbol> inferredTypes, int index,
                 selectedItem.Span,
                 selectedItem.DisplayText));
         }
+
+        internal override ImmutableHashSet<char> TriggerCharacters => ImmutableHashSet<char>.Empty;
     }
 }

src/Features/Core/Portable/Completion/LSPCompletionProvider.cs

@@ -12,6 +12,6 @@ internal abstract class LSPCompletionProvider : CommonCompletionProvider
         /// Defines the set of possible non-identifier trigger characters for this completion provider.
         /// Used by the LSP server to determine the trigger character set for completion.
         /// </summary>
-        internal virtual ImmutableHashSet<char> TriggerCharacters { get; } = ImmutableHashSet<char>.Empty;
+        internal abstract ImmutableHashSet<char> TriggerCharacters { get; }
     }
 }

src/Features/Core/Portable/Completion/SuggestionMode/SuggestionModeCompletionProvider.cs

@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+using System.Collections.Immutable;
 using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.CodeAnalysis.Options;
@@ -23,5 +24,7 @@ protected CompletionItem CreateEmptySuggestionModeItem()
             => CreateSuggestionModeItem(displayText: null, description: null);
 
         internal override bool IsInsertionTrigger(SourceText text, int position, OptionSet options) => false;
+
+        internal override ImmutableHashSet<char> TriggerCharacters => ImmutableHashSet<char>.Empty;
     }
 }

src/Features/VisualBasic/Portable/Completion/SuggestionMode/VisualBasicSuggestionModeCompletionProvider.vb

@@ -2,6 +2,7 @@
 ' The .NET Foundation licenses this file to you under the MIT license.
 ' See the LICENSE file in the project root for more information.
 
+Imports System.Collections.Immutable
 Imports System.Composition
 Imports System.Threading
 Imports Microsoft.CodeAnalysis
@@ -150,5 +151,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Completion.SuggestionMode
             Return Nothing
         End Function
 
+        Friend Overrides ReadOnly Property TriggerCharacters As ImmutableHashSet(Of Char) = ImmutableHashSet(Of Char).Empty
+
     End Class
 End Namespace

src/VisualStudio/VisualBasic/Impl/Snippets/SnippetCompletionProvider.vb

@@ -92,6 +92,8 @@ Namespace Microsoft.VisualStudio.LanguageServices.VisualBasic.Snippets
                 options.GetOption(CompletionOptions.TriggerOnTypingLetters, LanguageNames.VisualBasic)
         End Function
 
+        Friend Overrides ReadOnly Property TriggerCharacters As ImmutableHashSet(Of Char) = ImmutableHashSet(Of Char).Empty
+
         Public Sub Commit(completionItem As CompletionItem,
                           textView As ITextView,
                           subjectBuffer As ITextBuffer,