fix #639

Microsoft.DotNet.Interactive.FSharp/FSharpKernelHelpers.fs

@@ -4,9 +4,12 @@
 namespace Microsoft.DotNet.Interactive.FSharp
 
 open Microsoft.DotNet.Interactive
+open Microsoft.AspNetCore.Html
 
 module FSharpKernelHelpers =
     let display (value: obj) =
         Kernel.display value
+    let HTML (value: string) =
+        HtmlString value
     let Javascript (content: string) =
         Kernel.Javascript content

Microsoft.DotNet.Interactive.Rendering/DefaultHtmlFormatterSet.cs

@@ -72,9 +72,9 @@ private static ConcurrentDictionary<Type, ITypeFormatter> DefaultFormatters() =>
                     t.WriteTo(writer, HtmlEncoder.Default);
                 }),
 
-                [typeof(HtmlString)] = new HtmlFormatter<PocketView>((view, writer) => view.WriteTo(writer, HtmlEncoder.Default)),
+                [typeof(HtmlString)] = new HtmlFormatter<HtmlString>((view, writer) => view.WriteTo(writer, HtmlEncoder.Default)),
 
-                [typeof(JsonString)] = new HtmlFormatter<PocketView>((view, writer) => view.WriteTo(writer, HtmlEncoder.Default)),
+                [typeof(JsonString)] = new HtmlFormatter<JsonString>((view, writer) => view.WriteTo(writer, HtmlEncoder.Default)),
 
                 [typeof(PocketView)] = new HtmlFormatter<PocketView>((view, writer) => view.WriteTo(writer, HtmlEncoder.Default)),
 

Microsoft.DotNet.Interactive.Rendering/HtmlFormatter{T}.cs

@@ -26,7 +26,7 @@ public override void Format(T instance, TextWriter writer)
             _format(instance, writer);
         }
 
-        public override string MimeType => "text/html";
+        public override string MimeType => HtmlFormatter.MimeType;
 
         public static ITypeFormatter<T> Create(bool includeInternals = false)
         {

Microsoft.DotNet.Interactive.Rendering/PlainTextFormatter{T}.cs

@@ -42,7 +42,7 @@ public static ITypeFormatter<T> Create(bool includeInternals = false)
             return Default;
         }
 
-        public override string MimeType => "text/plain";
+        public override string MimeType => PlainTextFormatter.MimeType;
 
         public override void Format(T instance, TextWriter writer)
         {

Microsoft.DotNet.Interactive.Tests/AssertionExtensions.cs

@@ -38,5 +38,14 @@ public static AndWhichConstraint<ObjectAssertions, T> ContainSingle<T>(
 
             return new AndWhichConstraint<ObjectAssertions, T>(subject.Should(), subject);
         }
+
+        public static AndConstraint<GenericCollectionAssertions<IKernelEvent>> NotContainErrors(
+            this GenericCollectionAssertions<IKernelEvent> should) =>
+            should
+                .NotContain(e => e is ErrorProduced)
+                .And
+                .NotContain(e => e is CommandParseFailure)
+                .And
+                .NotContain(e => e is CommandFailed);
     }
 }

WorkspaceServer.Tests/Kernel/LanguageKernelRenderingTests.cs

@@ -1,6 +1,7 @@
 // Copyright (c) .NET Foundation and contributors. All rights reserved.
 // Licensed under the MIT license. See LICENSE file in the project root for full license information.
 
+using System;
 using System.Linq;
 using System.Reactive.Linq;
 using System.Threading.Tasks;
@@ -10,6 +11,7 @@
 using Microsoft.DotNet.Interactive.Commands;
 using Microsoft.DotNet.Interactive.Events;
 using Microsoft.DotNet.Interactive.Rendering;
+using Microsoft.DotNet.Interactive.Tests;
 using Pocket;
 using Xunit;
 using Xunit.Abstractions;
@@ -175,6 +177,30 @@ public async Task Value_display_and_update_are_in_right_order(Language language)
             valueEvents.Last().Should().BeOfType<DisplayedValueUpdated>();
         }
 
+        [Theory]
+        [InlineData(Language.CSharp, "display(HTML(\"<b>hi!</b>\"));")]
+        [InlineData(Language.FSharp, "display(HTML(\"<b>hi!</b>\"))")]
+        public async Task HTML_helper_emits_HTML_which_is_not_encoded_and_has_the_text_html_mime_type(
+            Language language, 
+            string code)
+        {
+            var kernel = CreateKernel(language);
+
+            var events = kernel.KernelEvents.ToSubscribedList();
+
+            await kernel.SubmitCodeAsync(code);
+
+            events.Should().NotContainErrors();
+
+            events.Should()
+                  .ContainSingle<DisplayedValueProduced>()
+                  .Which
+                  .FormattedValues
+                  .Should()
+                  .ContainSingle(f => f.Value.Equals("<b>hi!</b>") &&
+                                      f.MimeType == "text/html");
+        }
+
         [Theory]
         [InlineData(Language.CSharp)]
         [InlineData(Language.FSharp)]

WorkspaceServer/Packaging/PackageRestoreContext.cs

@@ -49,7 +49,7 @@ public async Task<AddNugetResult> AddPackage(
         {
             var requestedPackage = new NugetPackageReference(packageName, packageVersion, restoreSources);
 
-            if (!String.IsNullOrEmpty(packageName) && _nugetPackageReferences.TryGetValue(requestedPackage, out var _))
+            if (!string.IsNullOrEmpty(packageName) && _nugetPackageReferences.TryGetValue(requestedPackage, out var _))
             {
                 return new AddNugetPackageResult(false, requestedPackage);
             }