Migrate from Newtonsoft.Json to System.Text.Json with Source Generation

[Copilot]

Replaced JSON.NET with System.Text.Json throughout the library to use modern .NET serialization and eliminate security vulnerabilities.

Changes

Dependencies

• Added System.Text.Json 9.0.1 (fixes CVE in 8.0.4)
• Removed Newtonsoft.Json 13.0.3
• Removed Dapplo.HttpExtensions.JsonNet 1.1.2

Attribute Migration (100+ entity files)

• [JsonProperty("name")] → [JsonPropertyName("name")]
• [JsonObject] → removed (unnecessary in System.Text.Json)
• StringEnumConverter → JsonStringEnumConverter
• CustomDateTimeOffsetConverter → JiraDateTimeOffsetConverter

Core Infrastructure

• Created SystemTextJsonSerializer : IJsonSerializer to replace JsonNetJsonSerializer
• Created JiraJsonSerializerOptions for shared serialization configuration
• Created JiraJsonContext with source generation support for .NET 6+ (AOT-friendly, high-performance)
• Updated JiraClient to use new serializer

Source Generation

• Implemented compile-time JSON serialization for .NET 6.0 and greater
• Automatically activated when targeting modern .NET frameworks
• Provides better performance and AOT compatibility
• Falls back to reflection-based serialization for .NET Framework 4.8.1
• Includes all major entity types (Issue, User, Project, Board, Sprint, etc.) and collections

Code Patterns

// Before: Newtonsoft.Json
var jsonContent = new JObject { { "username", username }, { "password", password } };
var content = new StringContent(jsonContent.ToString(Formatting.None));

// After: System.Text.Json
var credentials = new { username, password };
var json = JsonSerializer.Serialize(credentials, JiraJsonSerializerOptions.Default);
var content = new StringContent(json);

// Before: JArray/JToken manipulation
if (!(customField is JArray jArray)) return null;
return jArray[0]?.ToObject<Sprint>();

// After: JsonElement
if (!(customField is JsonElement jsonElement)) return null;
var jArray = jsonElement.EnumerateArray().ToArray();
return JsonSerializer.Deserialize<Sprint>(jArray[0].GetRawText(), JiraJsonSerializerOptions.Default);

Dependency Impact

System.Text.Json is now required:

• Built-in for .NET 5.0+
• NuGet package for .NET Framework 4.8.1
• More performant than JSON.NET, actively maintained, no security vulnerabilities
• Source generation provides additional performance benefits for .NET 6+

Original prompt

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This section details on the original issue you should resolve

<issue_title>Replace the usage of json.net with System.Text.Json</issue_title> <issue_description>Replace the usage of json.net with System.Text.Json, if possible with code generation. Is it possible to remov3 the need for a dependency on System.Text.Json for the project using Dapplo.Jira?</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes dapplo/Dapplo.Jira#84

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