Fix build errors on .NET SDK 3.1.100 and fixup some code after review.

src/JsonRpc/RequestRouterBase.cs

@@ -99,7 +99,10 @@ public virtual async Task<ErrorResponse> RouteRequest(TDescriptor descriptor, Re
                     // TODO: Try / catch for Internal Error
                     try
                     {
-                        if (descriptor == default)
+                        // To avoid boxing, the best way to compare generics for equality is with EqualityComparer<T>.Default.
+                        // This respects IEquatable<T> (without boxing) as well as object.Equals, and handles all the Nullable<T> "lifted" nuances.
+                        // https://stackoverflow.com/a/864860
+                        if (EqualityComparer<TDescriptor>.Default.Equals(descriptor, default))
                         {
                             _logger.LogDebug("descriptor not found for Request ({Id}) {Method}", request.Id, request.Method);
                             return new MethodNotFound(request.Id, request.Method);

src/Protocol/Models/BooleanOr.cs

@@ -1,3 +1,5 @@
+using System.Collections.Generic;
+
 namespace OmniSharp.Extensions.LanguageServer.Protocol.Models
 {
     public class BooleanOr<T>
@@ -15,7 +17,11 @@ public BooleanOr(bool value)
             _bool = value;
         }
 
-        public bool IsValue => this._value != default;
+        // To avoid boxing, the best way to compare generics for equality is with EqualityComparer<T>.Default.
+        // This respects IEquatable<T> (without boxing) as well as object.Equals, and handles all the Nullable<T> "lifted" nuances.
+        // https://stackoverflow.com/a/864860
+        public bool IsValue => !EqualityComparer<T>.Default.Equals(_value, default);
+
         public T Value
         {
             get { return this._value; }

src/Protocol/Models/WorkspaceEdit.cs

@@ -13,7 +13,7 @@ public class WorkspaceEdit
         /// Holds changes to existing resources.
         /// </summary>
         [Optional]
-        [JsonConverter(typeof(DictionaryUriConverter<Uri, IEnumerable<TextEdit>>))]
+        [JsonConverter(typeof(AbsoluteUriKeyConverter<IEnumerable<TextEdit>>))]
         public IDictionary<Uri, IEnumerable<TextEdit>> Changes { get; set; }
         /// <summary>
         /// An array of `TextDocumentEdit`s to express changes to n different text documents

src/Protocol/Serialization/Converters/AbsoluteUriConverter.cs

@@ -42,46 +42,38 @@ public override void WriteJson(JsonWriter writer, Uri value, JsonSerializer seri
                 return;
             }
 
-            if (!(value is Uri uriValue))
-            {
-                throw new JsonSerializationException("The value must be a URI.");
-            }
-
-            writer.WriteValue(Convert(uriValue));
-        }
-
-        public static string Convert(Uri uri)
-        {
-            if (!uri.IsAbsoluteUri)
+            if (!value.IsAbsoluteUri)
             {
                 throw new JsonSerializationException("The URI value must be an absolute Uri. Relative URI instances are not allowed.");
             }
 
-            if (uri.IsFile)
+            if (value.IsFile)
             {
                 // First add the file scheme and ://
-                var builder = new StringBuilder(uri.Scheme)
+                var builder = new StringBuilder(value.Scheme)
                     .Append("://");
 
                 // UNC file paths use the Host
-                if (uri.HostNameType != UriHostNameType.Basic)
+                if (value.HostNameType != UriHostNameType.Basic)
                 {
-                    builder.Append(uri.Host);
+                    builder.Append(value.Host);
                 }
 
                 // Paths that start with a drive letter don't have a slash in the PathAndQuery
                 // but they need it in the final result.
-                if (uri.PathAndQuery[0] != '/')
+                if (value.PathAndQuery[0] != '/')
                 {
                     builder.Append('/');
                 }
 
                 // Lastly add the remaining parts of the URL
-                builder.Append(uri.PathAndQuery);
-                return builder.ToString();
+                builder.Append(value.PathAndQuery);
+                writer.WriteValue(builder.ToString());
+            }
+            else
+            {
+                writer.WriteValue(value.AbsoluteUri);
             }
-
-            return uri.AbsoluteUri;
         }
     }
 }

src/Protocol/Serialization/Converters/AbsoluteUriKeyConverter.cs

@@ -0,0 +1,104 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+using Newtonsoft.Json;
+
+namespace OmniSharp.Extensions.LanguageServer.Protocol.Serialization.Converters
+{
+    class AbsoluteUriKeyConverter<TValue> : JsonConverter<Dictionary<Uri, TValue>>
+    {
+        public override Dictionary<Uri, TValue> ReadJson(
+            JsonReader reader,
+            Type objectType,
+            Dictionary<Uri, TValue> existingValue,
+            bool hasExistingValue,
+            JsonSerializer serializer)
+        {
+            if (reader.TokenType != JsonToken.StartObject)
+            {
+                throw new JsonException();
+            }
+
+            var dictionary = new Dictionary<Uri, TValue>();
+
+            while (reader.Read())
+            {
+                if (reader.TokenType == JsonToken.EndObject)
+                {
+                    return dictionary;
+                }
+
+                // Get the key.
+                if (reader.TokenType != JsonToken.PropertyName)
+                {
+                    throw new JsonSerializationException($"The token type must be a property name. Given {reader.TokenType.ToString()}");
+                }
+
+                // Get the stringified Uri.
+                var key = new Uri((string)reader.Value, UriKind.RelativeOrAbsolute);
+                if (!key.IsAbsoluteUri)
+                {
+                    throw new JsonSerializationException($"The Uri must be absolute. Given: {reader.Value}");
+                }
+
+                // Get the value.
+                reader.Read();
+                var value = serializer.Deserialize<TValue>(reader);
+
+                // Add to dictionary.
+                dictionary.Add(key, value);
+            }
+
+            throw new JsonException();
+        }
+
+        public override void WriteJson(
+            JsonWriter writer,
+            Dictionary<Uri, TValue> value,
+            JsonSerializer serializer)
+        {
+            writer.WriteStartObject();
+
+            foreach (var kvp in value)
+            {
+                var uri = kvp.Key;
+                if (!uri.IsAbsoluteUri)
+                {
+                    throw new JsonSerializationException("The URI value must be an absolute Uri. Relative URI instances are not allowed.");
+                }
+
+                if (uri.IsFile)
+                {
+                    // First add the file scheme and ://
+                    var builder = new StringBuilder(uri.Scheme)
+                        .Append("://");
+
+                    // UNC file paths use the Host
+                    if (uri.HostNameType != UriHostNameType.Basic)
+                    {
+                        builder.Append(uri.Host);
+                    }
+
+                    // Paths that start with a drive letter don't have a slash in the PathAndQuery
+                    // but they need it in the final result.
+                    if (uri.PathAndQuery[0] != '/')
+                    {
+                        builder.Append('/');
+                    }
+
+                    // Lastly add the remaining parts of the URL
+                    builder.Append(uri.PathAndQuery);
+                    writer.WritePropertyName(builder.ToString());
+                }
+                else
+                {
+                    writer.WritePropertyName(uri.AbsoluteUri);
+                }
+
+                serializer.Serialize(writer, kvp.Value);
+            }
+
+            writer.WriteEndObject();
+        }
+    }
+}