Reduce allocations in the ImageElementConverter and ImageIdConverter Read methods (#78881)

* Reduce allocations in the ImageElementConverter and ImageIdConverter Read methods

These methods show up in the typing scenario in the razor speedometer test as about 0.9% (63 MB) of allocations.

1) Changed ImageIdConverter to be more like ImageElementConverter and not create a JsonDocument object to query
2) Changed several Utf8JsonReader.GetText calls to instead use Utf8JsonReader.CopyString
3) Changed JsonElement.GetString and new Guid(...) to instead use Utf8JsonReader.GetGuid()

Note that if this PR is merged, I'll also try to make a change to vslanguageserverclient to also do the same as that code has the same issues.

Author: ToddGrun

src/LanguageServer/Protocol/Protocol/Internal/Converters/ImageElementConverter.cs

@@ -9,6 +9,7 @@
 using Roslyn.Text.Adornments;
 
 namespace Roslyn.LanguageServer.Protocol;
+
 internal sealed class ImageElementConverter : JsonConverter<ImageElement>
 {
     public static readonly ImageElementConverter Instance = new();
@@ -20,6 +21,8 @@ public override ImageElement Read(ref Utf8JsonReader reader, Type typeToConvert,
             ImageId? imageId = null;
             string? automationName = null;
 
+            Span<char> scratchChars = stackalloc char[64];
+
             while (reader.Read())
             {
                 if (reader.TokenType == JsonTokenType.EndObject)
@@ -30,7 +33,11 @@ public override ImageElement Read(ref Utf8JsonReader reader, Type typeToConvert,
 
                 if (reader.TokenType == JsonTokenType.PropertyName)
                 {
-                    var propertyName = reader.GetString();
+                    var valueLength = reader.HasValueSequence ? reader.ValueSequence.Length : reader.ValueSpan.Length;
+
+                    var propertyNameLength = valueLength <= scratchChars.Length ? reader.CopyString(scratchChars) : -1;
+                    var propertyName = propertyNameLength >= 0 ? scratchChars[..propertyNameLength] : reader.GetString().AsSpan();
+
                     reader.Read();
                     switch (propertyName)
                     {
@@ -41,7 +48,10 @@ public override ImageElement Read(ref Utf8JsonReader reader, Type typeToConvert,
                             automationName = reader.GetString();
                             break;
                         case ObjectContentConverter.TypeProperty:
-                            if (reader.GetString() != nameof(ImageElement))
+                            var typePropertyLength = valueLength <= scratchChars.Length ? reader.CopyString(scratchChars) : -1;
+                            var typeProperty = typePropertyLength >= 0 ? scratchChars[..typePropertyLength] : reader.GetString().AsSpan();
+
+                            if (!typeProperty.SequenceEqual(nameof(ImageElement).AsSpan()))
                                 throw new JsonException($"Expected {ObjectContentConverter.TypeProperty} property value {nameof(ImageElement)}");
                             break;
                         default:
@@ -60,7 +70,10 @@ public override void Write(Utf8JsonWriter writer, ImageElement value, JsonSerial
         writer.WriteStartObject();
         writer.WritePropertyName(nameof(ImageElement.ImageId));
         ImageIdConverter.Instance.Write(writer, value.ImageId, options);
-        writer.WriteString(nameof(ImageElement.AutomationName), value.AutomationName);
+
+        if (value.AutomationName != null)
+            writer.WriteString(nameof(ImageElement.AutomationName), value.AutomationName);
+
         writer.WriteString(ObjectContentConverter.TypeProperty, nameof(ImageElement));
         writer.WriteEndObject();
     }

src/LanguageServer/Protocol/Protocol/Internal/Converters/ImageIdConverter.cs

@@ -8,6 +8,7 @@
 using Roslyn.Core.Imaging;
 
 namespace Roslyn.LanguageServer.Protocol;
+
 internal sealed class ImageIdConverter : JsonConverter<ImageId>
 {
     public static readonly ImageIdConverter Instance = new();
@@ -16,21 +17,53 @@ public override ImageId Read(ref Utf8JsonReader reader, Type objectType, JsonSer
     {
         if (reader.TokenType == JsonTokenType.StartObject)
         {
-            using var document = JsonDocument.ParseValue(ref reader);
-            var root = document.RootElement;
-            if (root.TryGetProperty(ObjectContentConverter.TypeProperty, out var typeProperty) && typeProperty.GetString() != nameof(ImageId))
+            Guid? guid = null;
+            int? id = null;
+
+            Span<char> scratchChars = stackalloc char[64];
+
+            while (reader.Read())
             {
-                throw new JsonException($"Expected {ObjectContentConverter.TypeProperty} property value {nameof(ImageId)}");
-            }
+                if (reader.TokenType == JsonTokenType.EndObject)
+                {
+                    if (guid is null || id is null)
+                        throw new JsonException("Expected properties Guid and Id to be present");
 
-            var guid = root.GetProperty(nameof(ImageId.Guid)).GetString() ?? throw new JsonException();
-            var id = root.GetProperty(nameof(ImageId.Id)).GetInt32();
-            return new ImageId(new Guid(guid), id);
-        }
-        else
-        {
-            throw new JsonException("Expected start object or null tokens");
+                    return new ImageId(guid.Value, id.Value);
+                }
+
+                if (reader.TokenType == JsonTokenType.PropertyName)
+                {
+                    var valueLength = reader.HasValueSequence ? reader.ValueSequence.Length : reader.ValueSpan.Length;
+
+                    var propertyNameLength = valueLength <= scratchChars.Length ? reader.CopyString(scratchChars) : -1;
+                    var propertyName = propertyNameLength >= 0 ? scratchChars[..propertyNameLength] : reader.GetString().AsSpan();
+
+                    reader.Read();
+                    switch (propertyName)
+                    {
+                        case nameof(ImageId.Guid):
+                            guid = reader.GetGuid();
+                            break;
+                        case nameof(ImageId.Id):
+                            id = reader.GetInt32();
+                            break;
+                        case ObjectContentConverter.TypeProperty:
+                            var typePropertyLength = valueLength <= scratchChars.Length ? reader.CopyString(scratchChars) : -1;
+                            var typeProperty = typePropertyLength >= 0 ? scratchChars[..typePropertyLength] : reader.GetString().AsSpan();
+
+                            if (!typeProperty.SequenceEqual(nameof(ImageId).AsSpan()))
+                                throw new JsonException($"Expected {ObjectContentConverter.TypeProperty} property value {nameof(ImageId)}");
+                            break;
+                        default:
+                            reader.Skip();
+                            break;
+                    }
+                }
+            }
         }
+
+        throw new JsonException("Expected start object or null tokens");
     }
 
     public override void Write(Utf8JsonWriter writer, ImageId value, JsonSerializerOptions options)