Migrate from Newtonsoft.Json to System.Text.Json

Replace Newtonsoft.Json 13.0.1 with System.Text.Json 8.0.5 across the
entire codebase. This eliminates the reflection-heavy Newtonsoft
dependency, a prerequisite for NativeAOT compilation.

Add GVFSJsonOptions.cs with shared JsonSerializerOptions, centralized
Serialize/Deserialize helpers, and registered custom converters.
Add EventMetadataConverter for AOT-safe Dictionary<string,object> handling.
Add VersionConverter for System.Version (no built-in STJ support).
Use runtime type dispatch in BaseResponse<T>.ToMessage() to preserve
derived-class properties during polymorphic serialization.
Replace [JsonProperty] with [JsonPropertyName] in telemetry types.
Replace JObject.Parse with JsonDocument in functional tests.
Change GitObjectSize readonly fields to properties (STJ ignores fields).
Add parameterless constructors where STJ deserialization requires them.
Set LangVersion=latest in Directory.Build.props.
Remove Newtonsoft.Json from all projects and Directory.Packages.props.

Assisted-by: Claude Opus 4.6
Signed-off-by: Tyrie Vella <tyrielv@gmail.com>

Author: tyrielv

Directory.Build.props

@@ -22,6 +22,7 @@
 
   <!-- Managed project properties -->
   <PropertyGroup Condition="'$(MSBuildProjectExtension)' == '.csproj'">
+    <LangVersion>latest</LangVersion>
     <RuntimeIdentifier>win-x64</RuntimeIdentifier>
     <PlatformTarget>x64</PlatformTarget>
     <BaseOutputPath>$(ProjectOutPath)bin\</BaseOutputPath>

Directory.Packages.props

@@ -6,7 +6,7 @@
 
   <ItemGroup>
     <!-- Serialization -->
-    <PackageVersion Include="Newtonsoft.Json" Version="13.0.1" />
+    <PackageVersion Include="System.Text.Json" Version="8.0.5" />
 
     <!-- Storage -->
     <PackageVersion Include="Microsoft.Data.Sqlite" Version="2.2.4" />
@@ -42,7 +42,6 @@
     -->
     <PackageVersion Include="System.CommandLine" Version="2.0.5" />
     <PackageVersion Include="System.IO.Pipes.AccessControl" Version="8.0.0" />
-    <PackageVersion Include="System.Text.Json" Version="8.0.5" />
   </ItemGroup>
 
 </Project>

GVFS/GVFS.Common/FileBasedDictionary.cs

@@ -1,9 +1,9 @@
-using GVFS.Common.FileSystem;
+using GVFS.Common.FileSystem;
 using GVFS.Common.Tracing;
-using Newtonsoft.Json;
 using System;
 using System.Collections.Concurrent;
 using System.Collections.Generic;
+using System.Text.Json;
 
 namespace GVFS.Common
 {
@@ -120,7 +120,7 @@ private bool TryParseAddLine(string line, out TKey key, out TValue value, out st
         {
             try
             {
-                KeyValuePair<TKey, TValue> kvp = JsonConvert.DeserializeObject<KeyValuePair<TKey, TValue>>(line);
+                KeyValuePair<TKey, TValue> kvp = GVFSJsonOptions.Deserialize<KeyValuePair<TKey, TValue>>(line);
                 key = kvp.Key;
                 value = kvp.Value;
             }
@@ -140,7 +140,7 @@ private bool TryParseRemoveLine(string line, out TKey key, out string error)
         {
             try
             {
-                key = JsonConvert.DeserializeObject<TKey>(line);
+                key = GVFSJsonOptions.Deserialize<TKey>(line);
             }
             catch (JsonException ex)
             {
@@ -162,7 +162,7 @@ private IEnumerable<string> GenerateDataLines()
         {
             foreach (KeyValuePair<TKey, TValue> kvp in this.data)
             {
-                yield return this.FormatAddLine(JsonConvert.SerializeObject(kvp).Trim());
+                yield return this.FormatAddLine(GVFSJsonOptions.Serialize(kvp).Trim());
             }
         }
     }

GVFS/GVFS.Common/GVFS.Common.csproj

@@ -8,7 +8,7 @@
   <ItemGroup>
     <PackageReference Include="LibGit2Sharp.NativeBinaries" />
     <PackageReference Include="Microsoft.Data.Sqlite" />
-    <PackageReference Include="Newtonsoft.Json" />
+    <PackageReference Include="System.Text.Json" />
     <PackageReference Include="SharpZipLib" />
   </ItemGroup>
 

GVFS/GVFS.Common/GVFSEnlistment.cs

@@ -2,9 +2,9 @@
 using GVFS.Common.Git;
 using GVFS.Common.NamedPipes;
 using GVFS.Common.Tracing;
-using Newtonsoft.Json;
 using System;
 using System.IO;
+using System.Text.Json;
 using System.Threading;
 
 namespace GVFS.Common
@@ -270,7 +270,7 @@ public static bool WaitUntilMounted(ITracer tracer, string pipeName, string enli
                         tracer.RelatedError($"{nameof(WaitUntilMounted)}: {errorMessage}");
                         return false;
                     }
-                    catch (JsonReaderException e)
+                    catch (JsonException e)
                     {
                         errorMessage = string.Format("Failed to parse response from GVFS.Mount.\n {0}", e);
                         tracer.RelatedError($"{nameof(WaitUntilMounted)}: {errorMessage}");

GVFS/GVFS.Common/GVFSJsonOptions.cs

@@ -0,0 +1,43 @@
+using System;
+using System.Text.Json;
+
+namespace GVFS.Common
+{
+    /// <summary>
+    /// Shared JsonSerializerOptions and helpers for the GVFS codebase.
+    /// PropertyNameCaseInsensitive preserves backward compatibility with
+    /// Newtonsoft.Json's default case-insensitive deserialization.
+    /// </summary>
+    public static class GVFSJsonOptions
+    {
+        public static readonly JsonSerializerOptions Default = new JsonSerializerOptions
+        {
+            PropertyNameCaseInsensitive = true,
+            Converters = { new VersionConverter(), new Tracing.EventMetadataConverter() },
+        };
+
+        /// <summary>
+        /// Serialize using the compile-time type. Use when <typeparamref name="T"/>
+        /// is the concrete type (not a base class with derived properties).
+        /// </summary>
+        public static string Serialize<T>(T value)
+        {
+            return JsonSerializer.Serialize(value, Default);
+        }
+
+        /// <summary>
+        /// Serialize using the runtime type. Use when calling from a base-class
+        /// method where compile-time type would lose derived-class properties
+        /// (e.g., BaseResponse&lt;T&gt;.ToMessage()).
+        /// </summary>
+        public static string Serialize(object value, Type inputType)
+        {
+            return JsonSerializer.Serialize(value, inputType, Default);
+        }
+
+        public static T Deserialize<T>(string json)
+        {
+            return JsonSerializer.Deserialize<T>(json, Default);
+        }
+    }
+}

GVFS/GVFS.Common/Http/CacheServerInfo.cs

@@ -1,5 +1,5 @@
-using Newtonsoft.Json;
-using System;
+using System;
+using System.Text.Json.Serialization;
 
 namespace GVFS.Common.Http
 {

GVFS/GVFS.Common/Http/ConfigHttpRequestor.cs

@@ -1,8 +1,8 @@
-using GVFS.Common.Tracing;
-using Newtonsoft.Json;
+using GVFS.Common.Tracing;
 using System;
 using System.Net;
 using System.Net.Http;
+using System.Text.Json;
 using System.Threading;
 
 namespace GVFS.Common.Http
@@ -66,10 +66,10 @@ public bool TryQueryGVFSConfig(bool logErrors, out ServerGVFSConfig serverGVFSCo
                         try
                         {
                             string configString = response.RetryableReadToEnd();
-                            ServerGVFSConfig config = JsonConvert.DeserializeObject<ServerGVFSConfig>(configString);
+                            ServerGVFSConfig config = GVFSJsonOptions.Deserialize<ServerGVFSConfig>(configString);
                             return new RetryWrapper<ServerGVFSConfig>.CallbackResult(config);
                         }
-                        catch (JsonReaderException e)
+                        catch (JsonException e)
                         {
                             return new RetryWrapper<ServerGVFSConfig>.CallbackResult(e, shouldRetry: false);
                         }

GVFS/GVFS.Common/Http/GitObjectsHttpRequestor.cs

@@ -1,8 +1,8 @@
-using GVFS.Common.Git;
+using GVFS.Common.Git;
 using GVFS.Common.Tracing;
-using Newtonsoft.Json;
 using System;
 using System.Collections.Generic;
+using System.Text.Json.Serialization;
 using System.Linq;
 using System.Net;
 using System.Net.Http;
@@ -81,7 +81,7 @@ public virtual List<GitObjectSize> QueryForFileSizes(IEnumerable<string> objectI
                         }
 
                         string objectSizesString = response.RetryableReadToEnd();
-                        List<GitObjectSize> objectSizes = JsonConvert.DeserializeObject<List<GitObjectSize>>(objectSizesString);
+                        List<GitObjectSize> objectSizes = GVFSJsonOptions.Deserialize<List<GitObjectSize>>(objectSizesString);
                         return new RetryWrapper<List<GitObjectSize>>.CallbackResult(objectSizes);
                     }
                 });
@@ -343,8 +343,8 @@ private string ObjectIdsJsonGenerator(long requestId, Func<IEnumerable<string>>
 
         public class GitObjectSize
         {
-            public readonly string Id;
-            public readonly long Size;
+            public string Id { get; set; }
+            public long Size { get; set; }
 
             [JsonConstructor]
             public GitObjectSize(string id, long size)

GVFS/GVFS.Common/InternalVerbParameters.cs

@@ -1,4 +1,3 @@
-using Newtonsoft.Json;
 
 namespace GVFS.Common
 {
@@ -23,12 +22,12 @@ public InternalVerbParameters(
 
         public static InternalVerbParameters FromJson(string json)
         {
-            return JsonConvert.DeserializeObject<InternalVerbParameters>(json);
+            return GVFSJsonOptions.Deserialize<InternalVerbParameters>(json);
         }
 
         public string ToJson()
         {
-            return JsonConvert.SerializeObject(this);
+            return GVFSJsonOptions.Serialize(this);
         }
     }
 }