Completion gets in the way attempting to line up arguments

src/EditorFeatures/Core/Implementation/IntelliSense/AsyncCompletion/CompletionSource.cs

@@ -63,6 +63,12 @@ internal CompletionSource(ITextView textView, IThreadingContext threadingContext
             // We would like to be sure that nobody changes buffers at the same time.
             AssertIsForeground();
 
+            if (_textView.Selection.Mode == TextSelectionMode.Box)
+            {
+                // No completion with multiple selection
+                return AsyncCompletionData.CompletionStartData.DoesNotParticipateInCompletion;
+            }
+
             var document = triggerLocation.Snapshot.GetOpenDocumentInCurrentContextWithChanges();
             if (document == null)
             {
@@ -109,6 +115,12 @@ internal CompletionSource(ITextView textView, IThreadingContext threadingContext
                 return true;
             }
 
+            // Enter does not trigger completion.
+            if (trigger.Reason == AsyncCompletionData.CompletionTriggerReason.Insertion && trigger.Character == '\n')
+            {
+                return false;
+            }
+
             //The user may be trying to invoke snippets through question-tab.
             // We may provide a completion after that.
             // Otherwise, tab should not be a completion trigger.

src/EditorFeatures/Test2/IntelliSense/CSharpCompletionCommandHandlerTests.vb

@@ -119,6 +119,29 @@ class C
             End Using
         End Function
 
+        <MemberData(NameOf(AllCompletionImplementations))>
+        <WpfTheory, Trait(Traits.Feature, Traits.Features.Completion)>
+        Public Async Function TestEnterDoesNotTriggerCompletion(completionImplementation As CompletionImplementation) As Task
+            Using state = TestStateFactory.CreateCSharpTestState(completionImplementation,
+                              <Document>
+using System;
+
+class C
+{
+    void M()
+    {
+        String.Equals("foo", "bar", $$StringComparison.CurrentCulture)
+    }
+}
+
+                              </Document>)
+
+                state.SendReturn()
+                Await state.WaitForAsynchronousOperationsAsync()
+                Await state.AssertNoCompletionSession()
+            End Using
+        End Function
+
         <MemberData(NameOf(AllCompletionImplementations))>
         <WpfTheory, Trait(Traits.Feature, Traits.Features.Completion)>
         Public Async Function TestNotAtStartOfExistingWord(completionImplementation As CompletionImplementation) As Task