Revert to using .NET Core SDK 3.1.423.

.devcontainer/devcontainer.json

@@ -0,0 +1,13 @@
+{
+    "extensions": [
+        "ms-dotnettools.csharp"
+    ],
+    "features": {
+        "ghcr.io/devcontainers/features/dotnet:1": {
+            "version": "3.1.423"
+        },
+        "ghcr.io/devcontainers/features/python:1": {
+            "version": "3.8"
+        }
+    }
+}

ci/steps-build-core.yml

@@ -4,9 +4,9 @@
 
 steps:
 - task: DotNetCoreInstaller@1
-  displayName: 'Install .NET Core SDK 6.0.401'
+  displayName: 'Install .NET Core SDK 3.1.423'
   inputs:
-    version: 6.0.401
+    version: 3.1.423
 
 - task: DotNetCoreCLI@2
   displayName: "Build and run unit tests on Core library"

examples/echo-kernel/echo-kernel.csproj

@@ -3,7 +3,7 @@
   <PropertyGroup>
     <PackAsTool>True</PackAsTool>
     <OutputType>Exe</OutputType>
-    <TargetFramework>net6.0</TargetFramework>
+    <TargetFramework>netcoreapp3.1</TargetFramework>
 
     <!--
       NB: We need for the tool command name to match the pattern dotnet-*,

examples/moon-kernel/moon-kernel.csproj

@@ -4,7 +4,7 @@
     <ToolCommandName>dotnet-imoon</ToolCommandName>
     <PackAsTool>True</PackAsTool>
     <OutputType>Exe</OutputType>
-    <TargetFramework>net6.0</TargetFramework>
+    <TargetFramework>netcoreapp3.1</TargetFramework>
     <Version>1.0</Version>
   </PropertyGroup>
 

src/Data/Protocol.cs

@@ -63,7 +63,7 @@ namespace Microsoft.Jupyter.Core.Protocol
         // each message will have the previous message's header in this field.
         public MessageHeader ParentHeader { get; set; }
 
-        public Dictionary<string, JToken> Metadata { get; set; } = new();
+        public Dictionary<string, JToken> Metadata { get; set; } = new Dictionary<string, JToken>();
 
         // FIXME: make not just an object.
         public MessageContent Content { get; set; }
@@ -205,7 +205,8 @@ namespace Microsoft.Jupyter.Core.Protocol
         public Dictionary<string, string> Data { get; set; }
 
         [JsonProperty("metadata")]
-        public Dictionary<string, Dictionary<string, JToken>> Metadata { get; set; } = new();
+        public Dictionary<string, Dictionary<string, JToken>> Metadata { get; set; }
+            = new Dictionary<string, Dictionary<string, JToken>>();
     }
 
     [JsonObject(MemberSerialization.OptIn)]
@@ -286,7 +287,8 @@ namespace Microsoft.Jupyter.Core.Protocol
         public Dictionary<string, string> Data { get; set; }
 
         [JsonProperty("metadata")]
-        public Dictionary<string, Dictionary<string, JToken>> Metadata { get; set; } = new();
+        public Dictionary<string, Dictionary<string, JToken>> Metadata { get; set; }
+            = new Dictionary<string, Dictionary<string, JToken>>();
 
         [JsonProperty("transient", NullValueHandling=NullValueHandling.Ignore)]
         public TransientDisplayData? Transient { get; set; } = null;

src/Engines/BaseEngine.cs

@@ -413,7 +413,7 @@ namespace Microsoft.Jupyter.Core
                             StreamName = stream,
                             Text = text
                         },
-                        Metadata = new()
+                        Metadata = new Dictionary<string, Newtonsoft.Json.Linq.JToken>()
                     }.AsReplyTo(parent)
                 );
             }
@@ -435,7 +435,7 @@ namespace Microsoft.Jupyter.Core
                     Transient = transient
                 };
                 #if DEBUG
-                Debug.Assert(displayData.Metadata is not null);
+                Debug.Assert(!(displayData.Metadata is null));
                 #endif
 
                 // Send the engine's output to stdout.
@@ -503,7 +503,7 @@ namespace Microsoft.Jupyter.Core
                     {
                         ZmqIdentities = message.ZmqIdentities,
                         ParentHeader = message.Header,
-                        Metadata = new(),
+                        Metadata = new Dictionary<string, Newtonsoft.Json.Linq.JToken>(),
                         Content = null,
                         Header = new MessageHeader
                         {

src/Engines/ExecuteRequestHandler.cs

@@ -63,7 +63,7 @@ namespace Microsoft.Jupyter.Core
                 {
                     ZmqIdentities = message.ZmqIdentities,
                     ParentHeader = message.Header,
-                    Metadata = new(),
+                    Metadata = new Dictionary<string, Newtonsoft.Json.Linq.JToken>(),
                     Content = new ExecuteInputContent
                     {
                         Code = code,
@@ -115,7 +115,7 @@ namespace Microsoft.Jupyter.Core
                     {
                         ZmqIdentities = message.ZmqIdentities,
                         ParentHeader = message.Header,
-                        Metadata = new(),
+                        Metadata = new Dictionary<string, Newtonsoft.Json.Linq.JToken>(),
                         Content = new ExecuteResultContent
                         {
                             ExecutionCount = executionCount,
@@ -142,7 +142,7 @@ namespace Microsoft.Jupyter.Core
                 {
                     ZmqIdentities = message.ZmqIdentities,
                     ParentHeader = message.Header,
-                    Metadata = new(),
+                    Metadata = new Dictionary<string, Newtonsoft.Json.Linq.JToken>(),
                     Content = new ExecuteReplyContent
                     {
                         ExecuteStatus = engineResponse.Status,
@@ -168,7 +168,7 @@ namespace Microsoft.Jupyter.Core
                 {
                     ZmqIdentities = message.ZmqIdentities,
                     ParentHeader = message.Header,
-                    Metadata = new(),
+                    Metadata = new Dictionary<string, Newtonsoft.Json.Linq.JToken>(),
                     Content = new ExecuteReplyContent
                     {
                         ExecuteStatus = ExecuteStatus.Abort,

src/Extensions/Conversions.cs

@@ -42,7 +42,7 @@ namespace Microsoft.Jupyter.Core
             new EncodedData
             {
                 Data = data,
-                Metadata = new()
+                Metadata = new Dictionary<string, Newtonsoft.Json.Linq.JToken>()
             };
 
         /// <summary>

src/Extensions/Extensions.cs

@@ -53,7 +53,7 @@ namespace Microsoft.Jupyter.Core
                     {
                         ExecutionState = state
                     },
-                    Metadata = new()
+                    Metadata = new Dictionary<string, JToken>()
                 }.AsReplyTo(message)
             );
         }

src/GlobalUsings.cs

@@ -1,8 +0,0 @@
-// Copyright (c) Microsoft Corporation.
-// Licensed under the MIT License.
-
-global using System;
-global using System.Collections.Generic;
-global using System.Collections.Immutable;
-global using System.Linq;
-global using System.Threading;

src/ResultEncoding/DisplayData.cs

@@ -35,8 +35,8 @@ namespace Microsoft.Jupyter.Core
         public static MimeBundle Empty() =>
             new MimeBundle
             {
-                Data = new(),
-                Metadata = new()
+                Data = new Dictionary<string, string>(),
+                Metadata = new Dictionary<string, Dictionary<string, JToken>>()
             };
     }
 

src/Servers/ShellServer.cs

@@ -190,7 +190,7 @@ namespace Microsoft.Jupyter.Core
                     {
                         ZmqIdentities = message.ZmqIdentities,
                         ParentHeader = message.Header,
-                        Metadata = new(),
+                        Metadata = new Dictionary<string, Newtonsoft.Json.Linq.JToken>(),
                         Content = this.context.Properties.AsKernelInfoReply(),
                         Header = new MessageHeader
                         {

src/jupyter-core.csproj

@@ -3,7 +3,7 @@
   <PropertyGroup>
     <OutputType>Library</OutputType>
     <TargetFramework>netstandard2.1</TargetFramework>
-    <LangVersion>10.0</LangVersion>
+    <LangVersion>8.0</LangVersion>
 
     <AssemblyName>Microsoft.Jupyter.Core</AssemblyName>
     <Version Condition=" '$(BUILD_MAJOR)' != ''  ">$(BUILD_MAJOR).$(BUILD_MINOR).0.0</Version>

tests/core/core.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>net6.0</TargetFramework>
+    <TargetFramework>netcoreapp3.1</TargetFramework>
     <IsPackable>false</IsPackable>
     <IsTestProject>true</IsTestProject>
     <AssemblyName>Microsoft.Jupyter.Core.Tests</AssemblyName>