Suppress diagnostics entirely for the preview for add-nuget.

src/EditorFeatures/Core/Implementation/Diagnostics/AbstractDiagnosticsTaggerProvider.TaggerProvider.cs

@@ -149,9 +149,7 @@ private void ProduceTags(TaggerContext<TTag> context, DocumentSnapshotSpan spanT
             }
 
             private bool IsSuppressed(NormalizedSnapshotSpanCollection suppressedSpans, SnapshotSpan span)
-            {
-                return suppressedSpans != null && suppressedSpans.IntersectsWith(span);
-            }
+                => suppressedSpans != null && suppressedSpans.IntersectsWith(span);
 
             internal void OnDiagnosticsUpdated(DiagnosticsUpdatedArgs e, SourceText sourceText, ITextSnapshot editorSnapshot)
             {

src/Features/CSharp/Portable/AddImport/CSharpAddImportCodeFixProvider.cs

@@ -520,12 +520,8 @@ private string GetUsingDirectiveString(INamespaceOrTypeSymbol namespaceOrTypeSym
         {
             var root = GetCompilationUnitSyntaxNode(contextNode, cancellationToken);
 
-            // Suppress diagnostics on the import we create.  Because we only get here when we are 
-            // adding a nuget package, it is certainly the case that in the preview this will not
-            // bind properly.  It will look silly to show such an error, so we just suppress things.
             var usingDirective = SyntaxFactory.UsingDirective(
-                CreateNameSyntax(namespaceParts, namespaceParts.Count - 1)).WithAdditionalAnnotations(
-                    SuppressDiagnosticsAnnotation.Create());
+                CreateNameSyntax(namespaceParts, namespaceParts.Count - 1));
 
             var compilation = await document.Project.GetCompilationAsync(cancellationToken).ConfigureAwait(false);
             var service = document.GetLanguageService<IAddImportsService>();

src/Features/Core/Portable/AddImport/CodeActions/PackageReference.InstallPackageAndAddImportCodeAction.cs

@@ -76,7 +76,16 @@ private async Task<Solution> GetUpdatedSolutionAsync(CancellationToken cancellat
                     var oldText = await _oldDocument.GetTextAsync(cancellationToken).ConfigureAwait(false);
                     var newText = oldText.WithChanges(_textChanges);
 
-                    return _oldDocument.WithText(newText).Project.Solution;
+                    var newDocument = _oldDocument.WithText(newText);
+                    var newRoot = await newDocument.GetSyntaxRootAsync(cancellationToken).ConfigureAwait(false);
+
+                    // Suppress diagnostics on the import we create.  Because we only get here when we are 
+                    // adding a nuget package, it is certainly the case that in the preview this will not
+                    // bind properly.  It will look silly to show such an error, so we just suppress things.
+                    var updatedRoot = newRoot.WithAdditionalAnnotations(SuppressDiagnosticsAnnotation.Create());
+                    var updatedDocument = newDocument.WithSyntaxRoot(updatedRoot);
+
+                    return updatedDocument.Project.Solution;
                 }
 
                 /// <summary>

src/Features/VisualBasic/Portable/AddImport/VisualBasicAddImportCodeFixProvider.vb

@@ -381,11 +381,6 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.AddImport
             Dim nameSyntax = CreateNameSyntax(nameSpaceParts, nameSpaceParts.Count - 1)
             Dim importsStatement = GetImportsStatement(nameSyntax)
 
-            ' Suppress diagnostics on the import we create.  Because we only get here when we are 
-            ' adding a NuGet package, it is certainly the case that in the preview this will not
-            ' bind properly.  It will look silly to show such an error, so we just suppress things.
-            importsStatement = importsStatement.WithAdditionalAnnotations(SuppressDiagnosticsAnnotation.Create())
-
             Return AddImportAsync(
                 contextNode, Document, placeSystemNamespaceFirst,
                 importsStatement, cancellationToken)