Add a test for committing C# named parameters on :

src/EditorFeatures/Test2/IntelliSense/CSharpCompletionCommandHandlerTests.vb

@@ -1929,5 +1929,26 @@ class Program
                 Await state.AssertSelectedCompletionItem("Add", description:="void List<T>.Add(T item)")
             End Using
         End Function
+
+        <WpfFact, Trait(Traits.Feature, Traits.Features.Completion)>
+        Public Async Function TestCommitNamedParameterWithColon() As Task
+            Using state = TestState.CreateCSharpTestState(
+                           <Document><![CDATA[
+using System.Collections.Generic;
+
+class Program
+{
+    static void Main(int args)
+    {
+        Main(args$$
+    }
+}]]></Document>, extraExportedTypes:={GetType(CSharpEditorFormattingService)}.ToList())
+
+                state.SendInvokeCompletionList()
+                state.SendTypeChars(":")
+                Await state.AssertNoCompletionSession()
+                Assert.Contains("args:", state.GetLineTextFromCaretPosition())
+            End Using
+        End Function
     End Class
 End Namespace
\ No newline at end of file

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

@@ -22,7 +22,10 @@ namespace Microsoft.CodeAnalysis.CSharp.Completion.Providers
     internal partial class NamedParameterCompletionProvider : CommonCompletionProvider, IEqualityComparer<IParameterSymbol>
     {
         private const string ColonString = ":";
-        private static readonly CompletionItemRules CompletionItemRules = CompletionItemRules.Default
+
+        // Explicitly remove ":" from the set of filter characters because (by default)
+        // any character that appears in DisplayText gets treated as a filter char.
+        private static readonly CompletionItemRules s_rules = CompletionItemRules.Default
             .WithFilterCharacterRule(CharacterSetModificationRule.Create(CharacterSetModificationKind.Remove, ':'));
 
         internal override bool IsInsertionTrigger(SourceText text, int characterPosition, OptionSet options)
@@ -98,7 +101,7 @@ public override async Task ProvideCompletionsAsync(CompletionContext context)
                     symbol: parameter,
                     contextPosition: token.SpanStart,
                     filterText: escapedName,
-                    rules: CompletionItemRules,
+                    rules: s_rules,
                     matchPriority: SymbolMatchPriority.PreferNamedArgument));
             }
         }