Roslyn incremental source generator that:

1. Reads appsettings.json from AdditionalFiles
2. Parses JSON into a tree with System.Text.Json
3. Infers C# types from JSON values
4. Generates settings classes + DI registration extension method

All generated code is AOT-compatible (no reflection).

JsonParser → TypeInference → ClassModel → CodeEmitter → SourceGenerator → DI Registration

• SettingsNode — tree model representing a JSON section
• JsonParser — parse JSON string into SettingsNode tree
• Type inference: string, int, long, double, bool, array, nested object
• Naming: convert camelCase/snake_case keys → PascalCase property names

• CodeEmitter — renders a SettingsNode tree into C# source text
• Each top-level JSON object → {Name}Settings class
• Nested objects → nested or separate classes
• Properties use { get; init; } for immutability
• Arrays → List<T> or T[]
• Proper #nullable enable, namespace wrapping

• Generate AddAppSettings(this IServiceCollection, IConfiguration) extension
• Bind each section: services.Configure<DatabaseSettings>(config.GetSection("Database"))
• Static, no reflection — AOT safe

• AppSettingsGenerator : IIncrementalGenerator
• Register AdditionalFiles provider filtered to appsettings.json
• Incremental: only re-run when file content changes
• Combine parsing + emitting into generated source output

• [SettingsType] marker attribute (generated) to customize type inference
• Optional [Required] and [Range] attribute generation

• Empty JSON / missing file handling
• Diagnostic reporting for parse errors
• Handle duplicate keys, reserved C# keywords as property names

For consumers:

// In .csproj — just add the package, mark appsettings.json as AdditionalFiles
<AdditionalFiles Include="appsettings.json" />

// Generated code auto-available:
builder.Services.AddAppSettings(builder.Configuration);

// Use via DI:
public MyService(IOptions<DatabaseSettings> db) { ... }

Generated types:

• {SectionName}Settings class per top-level JSON section
• ServiceCollectionExtensions.AddAppSettings() extension method

• Unit tests: JsonParser, type inference, CodeEmitter individually
• Integration tests: full generator driver → verify generated source compiles
• Real-world JSON samples: complex nested configs, arrays, mixed types