Start engine services in Start() instead of constructor.

build/test.ps1

@@ -43,6 +43,10 @@ function Test-One {
             --no-build `
             --logger trx `
             --filter $_ `
+            <# Enable additional output from the test logger, but
+               without also turning on lots of additional noise from msbuild.
+            #> `
+            --logger:"console;verbosity=detailed" `
             /property:DefineConstants=$Env:ASSEMBLY_CONSTANTS `
             /property:InformationalVersion=$Env:SEMVER_VERSION `
             /property:Version=$Env:ASSEMBLY_VERSION

src/Core/Loggers/NugetLogger.cs

@@ -1,5 +1,6 @@
 // Copyright (c) Microsoft Corporation. All rights reserved.
 // Licensed under the MIT License.
+#nullable enable
 
 using System;
 using System.Collections.Generic;
@@ -14,31 +15,24 @@ namespace Microsoft.Quantum.IQSharp.Common
     /// </summary>
     public class NuGetLogger : NuGet.Common.LoggerBase
     {
-        private ILogger _logger { get; set; }
+        private ILogger? _logger { get; set; }
         public List<NuGet.Common.ILogMessage> Logs { get; private set; }
 
-        public NuGetLogger(ILogger logger)
+        public NuGetLogger(ILogger? logger)
         {
             _logger = logger;
             this.Logs = new List<NuGet.Common.ILogMessage>();
         }
 
-        public static LogLevel MapLevel(NuGet.Common.LogLevel original)
-        {
-            switch (original)
+        public static LogLevel MapLevel(NuGet.Common.LogLevel original) =>
+            original switch
             {
-                case NuGet.Common.LogLevel.Error:
-                    return LogLevel.Error;
-                case NuGet.Common.LogLevel.Warning:
-                    return LogLevel.Warning;
-                case NuGet.Common.LogLevel.Information:
-                    return LogLevel.Information;
-                case NuGet.Common.LogLevel.Debug:
-                    return LogLevel.Debug;
-                default:
-                    return LogLevel.Trace;
-            }
-        }
+                NuGet.Common.LogLevel.Error => LogLevel.Error,
+                NuGet.Common.LogLevel.Warning => LogLevel.Warning,
+                NuGet.Common.LogLevel.Information => LogLevel.Information,
+                NuGet.Common.LogLevel.Debug => LogLevel.Debug,
+                _ => LogLevel.Trace
+            };
 
         public override void Log(NuGet.Common.ILogMessage m)
         {

src/Core/References/NugetPackages.cs

@@ -111,7 +111,7 @@ public IEnumerable<SourceRepository> Repositories
 
         public NugetPackages(
             IOptions<Settings> config,
-            ILogger<NugetPackages> logger
+            ILogger<NugetPackages>? logger
         )
         {
             this.Logger = new NuGetLogger(logger);

src/Jupyter/Jupyter.csproj

@@ -35,7 +35,7 @@
   </ItemGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.Jupyter.Core" Version="1.5.124273" />
+    <PackageReference Include="Microsoft.Jupyter.Core" Version="1.5.124810" />
     <PackageReference Include="System.Reactive" Version="4.3.2" />
   </ItemGroup>
 

src/Kernel/CustomShell/ClientInfoHandler.cs

@@ -17,34 +17,34 @@ namespace Microsoft.Quantum.IQSharp.Kernel
     internal class ClientInfoContent : MessageContent
     {
         [JsonProperty("hosting_environment")]
-        public string HostingEnvironment { get; set; }
+        public string? HostingEnvironment { get; set; }
 
         [JsonProperty("iqsharp_version")]
-        public string IQSharpVersion { get; set; }
+        public string? IQSharpVersion { get; set; }
 
         [JsonProperty("user_agent")]
-        public string UserAgent { get; set; }
+        public string? UserAgent { get; set; }
 
         [JsonProperty("client_id")]
-        public string ClientId { get; set; }
+        public string? ClientId { get; set; }
 
         [JsonProperty("client_isnew")]
         public bool? ClientIsNew { get; set; }
 
         [JsonProperty("client_host")]
-        public string ClientHost { get; set; }
+        public string? ClientHost { get; set; }
 
         [JsonProperty("client_origin")]
-        public string ClientOrigin { get; set; }
+        public string? ClientOrigin { get; set; }
 
         [JsonProperty("client_first_origin")]
-        public string ClientFirstOrigin { get; set; }
+        public string? ClientFirstOrigin { get; set; }
 
         [JsonProperty("client_language")]
-        public string ClientLanguage { get; set; }
+        public string? ClientLanguage { get; set; }
 
         [JsonProperty("client_country")]
-        public string ClientCountry { get; set; }
+        public string? ClientCountry { get; set; }
 
         [JsonProperty("telemetry_opt_out")]
         public bool? TelemetryOptOut { get; set; }
@@ -69,7 +69,7 @@ internal static ClientInfoContent AsClientInfoContent(this IMetadataController m
     /// </summary>
     internal class ClientInfoHandler : IShellHandler
     {
-        public string UserAgent { get; private set; }
+        public string? UserAgent { get; private set; }
         private readonly ILogger<ClientInfoHandler> logger;
         private readonly IMetadataController metadata;
         private readonly IShellServer shellServer;

src/Kernel/CustomShell/EchoHandler.cs

@@ -13,7 +13,7 @@ namespace Microsoft.Quantum.IQSharp.Kernel
     internal class EchoReplyContent : MessageContent
     {
         [JsonProperty("value")]
-        public string Value { get; set; }
+        public string Value { get; set; } = "";
     }
 
     /// <summary>
@@ -44,7 +44,7 @@ IShellServer shellServer
         public async Task HandleAsync(Message message)
         {
             // Find out the thing we need to echo back.
-            var value = (message.Content as UnknownContent).Data["value"] as string;
+            var value = (message.Content as UnknownContent)?.Data?["value"] as string ?? "";
             // Send the echo both as an output and as a reply so that clients
             // can test both kinds of callbacks.
             await Task.Run(() =>

src/Kernel/CustomShell/MessageExtensions.cs

@@ -22,18 +22,28 @@ public static class MessageExtensions
         public static T To<T>(this Message message)
             where T : MessageContent
         {
-            var content = (message.Content as UnknownContent);
-            var result = Activator.CreateInstance<T>();
-            foreach (var property in typeof(T).GetProperties().Where(p => p.CanWrite))
+            if (message.Content is UnknownContent content)
             {
-                var jsonPropertyAttribute = property.GetCustomAttributes(true).OfType<JsonPropertyAttribute>().FirstOrDefault();
-                var propertyName = jsonPropertyAttribute?.PropertyName ?? property.Name;
-                if (content.Data.TryGetValue(propertyName, out var value))
+                var result = Activator.CreateInstance<T>();
+                foreach (var property in typeof(T).GetProperties().Where(p => p.CanWrite))
                 {
-                    property.SetValue(result, content.Data[propertyName]);
+                    var jsonPropertyAttribute = property.GetCustomAttributes(true).OfType<JsonPropertyAttribute>().FirstOrDefault();
+                    var propertyName = jsonPropertyAttribute?.PropertyName ?? property.Name;
+                    if (content.Data.TryGetValue(propertyName, out var value))
+                    {
+                        property.SetValue(result, content.Data[propertyName]);
+                    }
                 }
+                return result;
+            }
+            else if (message.Content is T decoded)
+            {
+                return decoded;
+            }
+            else
+            {
+                throw new Exception($"Attempted to convert a message with content type {message.Content.GetType()} to content type {typeof(T)}; can only convert from unknown content or subclasses of the desired content type.");
             }
-            return result;
         }
     }
 }

src/Kernel/IQSharpEngine.cs

@@ -19,6 +19,7 @@
 using System.Threading.Tasks;
 using System.Collections.Immutable;
 using Microsoft.Quantum.IQSharp.AzureClient;
+using Microsoft.Quantum.QsCompiler.BondSchemas;
 
 namespace Microsoft.Quantum.IQSharp.Kernel
 {
@@ -29,6 +30,24 @@ namespace Microsoft.Quantum.IQSharp.Kernel
     public class IQSharpEngine : BaseEngine
     {
         private readonly PerformanceMonitor performanceMonitor;
+        private readonly IConfigurationSource configurationSource;
+        private readonly IServiceProvider services;
+        private readonly ILogger<IQSharpEngine> logger;
+
+        // NB: These properties may be null if the engine has not fully started
+        //     up yet.
+        internal ISnippets? Snippets { get; private set; } = null;
+
+        internal ISymbolResolver? SymbolsResolver { get; private set; } = null;
+
+        internal IMagicSymbolResolver? MagicResolver { get; private set; } = null;
+
+        internal IWorkspace? Workspace { get; private set; } = null;
+
+        private TaskCompletionSource<bool> initializedSource = new TaskCompletionSource<bool>();
+
+        /// <inheritdoc />
+        public override Task Initialized => initializedSource.Task;
 
         /// <summary>
         /// The main constructor. It expects an `ISnippets` instance that takes care
@@ -41,20 +60,42 @@ public IQSharpEngine(
             IServiceProvider services,
             IConfigurationSource configurationSource,
             PerformanceMonitor performanceMonitor,
-            IShellRouter shellRouter,
-            IEventService eventService,
-            IMagicSymbolResolver magicSymbolResolver,
-            IReferences references
+            IShellRouter shellRouter
         ) : base(shell, shellRouter, context, logger, services)
         {
             this.performanceMonitor = performanceMonitor;
             performanceMonitor.Start();
+            this.configurationSource = configurationSource;
+            this.services = services;
+            this.logger = logger;
+        }
+
+        /// <inheritdoc />
+        public override void Start()
+        {
+            base.Start();
 
+            // Before anything else, make sure to start the right background
+            // thread on the Q# compilation loader to initialize serializers
+            // and deserializers. Since that runs in the background, starting
+            // the engine should not be blocked, and other services can
+            // continue to initialize while the Q# compilation loader works.
+            //
+            // For more details, see:
+            //     https://github.com/microsoft/qsharp-compiler/pull/727
+            //     https://github.com/microsoft/qsharp-compiler/pull/810
+            logger.LogDebug("Loading serialization and deserialziation protocols.");
+            Protocols.Initialize();
+
+            logger.LogDebug("Getting services required to start IQ# engine.");
             this.Snippets = services.GetService<ISnippets>();
             this.SymbolsResolver = services.GetService<ISymbolResolver>();
-            this.MagicResolver = magicSymbolResolver;
+            this.MagicResolver = services.GetService<IMagicSymbolResolver>();
             this.Workspace = services.GetService<IWorkspace>();
+            var references = services.GetService<IReferences>();
+            var eventService = services.GetService<IEventService>();
 
+            logger.LogDebug("Registering IQ# display and JSON encoders.");
             RegisterDisplayEncoder(new IQSharpSymbolToHtmlResultEncoder());
             RegisterDisplayEncoder(new IQSharpSymbolToTextResultEncoder());
             RegisterDisplayEncoder(new TaskStatusToTextEncoder());
@@ -71,13 +112,15 @@ IReferences references
                 .Concat(AzureClient.JsonConverters.AllConverters)
                 .ToArray());
 
+            logger.LogDebug("Registering IQ# symbol resolvers.");
             RegisterSymbolResolver(this.SymbolsResolver);
             RegisterSymbolResolver(this.MagicResolver);
 
+            logger.LogDebug("Loading known assemblies and registering package loading.");
             RegisterPackageLoadedEvent(services, logger, references);
 
             // Handle new shell messages.
-            shellRouter.RegisterHandlers<IQSharpEngine>();
+            ShellRouter.RegisterHandlers<IQSharpEngine>();
 
             // Report performance after completing startup.
             performanceMonitor.Report();
@@ -86,8 +129,12 @@ IReferences references
                 Process.GetCurrentProcess().Id
             );
 
-
             eventService?.TriggerServiceInitialized<IExecutionEngine>(this);
+
+            var initializedSuccessfully = initializedSource.TrySetResult(true);
+            #if DEBUG
+                Debug.Assert(initializedSuccessfully, "Was unable to complete initialization task.");
+            #endif
         }
 
         /// <summary>
@@ -108,14 +155,17 @@ private void RegisterPackageLoadedEvent(IServiceProvider services, ILogger logge
             // Register new display encoders when packages load.
             references.PackageLoaded += (sender, args) =>
             {
-                logger.LogDebug("Scanning for display encoders after loading {Package}.", args.PackageId);
+                logger.LogDebug("Scanning for display encoders and magic symbols after loading {Package}.", args.PackageId);
                 foreach (var assembly in references.Assemblies
                                                    .Select(asm => asm.Assembly)
                                                    .Where(asm => !knownAssemblies.Contains(asm.GetName()))
                 )
                 {
                     // Look for display encoders in the new assembly.
-                    logger.LogDebug("Found new assembly {Name}, looking for display encoders.", assembly.FullName);
+                    logger.LogDebug("Found new assembly {Name}, looking for display encoders and magic symbols.", assembly.FullName);
+                    // Use the magic resolver to find magic symbols in the new assembly;
+                    // it will cache the results for the next magic resolution.
+                    this.MagicResolver?.FindMagic(new AssemblyInfo(assembly));
 
                     // If types from an assembly cannot be loaded, log a warning and continue.
                     var relevantTypes = Enumerable.Empty<Type>();
@@ -167,14 +217,6 @@ private void RegisterPackageLoadedEvent(IServiceProvider services, ILogger logge
             };
         }
 
-        internal ISnippets Snippets { get; }
-
-        internal ISymbolResolver SymbolsResolver { get; }
-
-        internal ISymbolResolver MagicResolver { get; }
-
-        internal IWorkspace Workspace { get; }
-
         /// <summary>
         /// This is the method used to execute Jupyter "normal" cells. In this case, a normal
         /// cell is expected to have a Q# snippet, which gets compiled and we return the name of
@@ -188,9 +230,15 @@ public override async Task<ExecutionResult> ExecuteMundane(string input, IChanne
             {
                 try
                 {
-                    await Workspace.Initialization;
+                    await this.Initialized;
+                    // Once the engine is initialized, we know that Workspace
+                    // and Snippets are both not-null.
+                    var workspace = this.Workspace!;
+                    var snippets = this.Snippets!;
+
+                    await workspace.Initialization;
 
-                    var code = Snippets.Compile(input);
+                    var code = snippets.Compile(input);
 
                     foreach (var m in code.warnings) { channel.Stdout(m); }
 

src/Kernel/Kernel.csproj

@@ -6,6 +6,7 @@
     <RootNamespace>Microsoft.Quantum.IQSharp.Kernel</RootNamespace>
     <AssemblyName>Microsoft.Quantum.IQSharp.Kernel</AssemblyName>
     <GenerateDocumentationFile>true</GenerateDocumentationFile>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
 
   <ItemGroup>

src/Kernel/KernelApp/IQSharpKernelApp.cs

@@ -63,7 +63,7 @@ public static class KernelEventsExtensions
         /// </summary>
         /// <param name="eventService">The event service where the EventSubPub lives</param>
         /// <returns>The typed EventPubSub for the KernelStarted event</returns>
-        public static EventPubSub<KernelStartedEvent, IQSharpKernelApp> OnKernelStarted(this IEventService eventService)
+        public static EventPubSub<KernelStartedEvent, IQSharpKernelApp>? OnKernelStarted(this IEventService eventService)
         {
             return eventService?.Events<KernelStartedEvent, IQSharpKernelApp>();
         }
@@ -73,7 +73,7 @@ public static EventPubSub<KernelStartedEvent, IQSharpKernelApp> OnKernelStarted(
         /// </summary>
         /// <param name="eventService">The event service where the EventSubPub lives</param>
         /// <returns>The typed EventPubSub for the KernelStopped event</returns>
-        public static EventPubSub<KernelStoppedEvent, IQSharpKernelApp> OnKernelStopped(this IEventService eventService)
+        public static EventPubSub<KernelStoppedEvent, IQSharpKernelApp>? OnKernelStopped(this IEventService eventService)
         {
             return eventService?.Events<KernelStoppedEvent, IQSharpKernelApp>();
         }