DtoSrcGen

This project is inspired by Utility Types from Typescript.

Source generator that builds DTO partial classes from existing models using attributes.

What it does

• Generates constructors and properties for partial classes annotated with attributes from DtoSrcGen.Models.
• Supports Pick, Omit, Readonly, Required, and Union patterns to shape DTOs without hand-written boilerplate.
• Supports GenerateDefaultCtor option on all attributes to control whether an empty DTO constructor is generated.
• Emits diagnostics when members are missing/duplicated and when language features (e.g., required) are unavailable.

Getting started

1. Add references to your project file:

  <ItemGroup>
    <ProjectReference Include="..\src\DtoSrcGen.Models\DtoSrcGen.Models.csproj" />
    <ProjectReference Include="..\src\DtoSrcGen\DtoSrcGen.csproj"
                      OutputItemType="Analyzer"
                      ReferenceOutputAssembly="false" />
  </ItemGroup>

2. Annotate partial DTOs:

using DtoSrcGen;

[Omit(typeof(User), nameof(User.Id), nameof(User.Age))]
public partial class DtoAge { }

[Pick(typeof(User), nameof(User.Id), nameof(User.Name))]
public partial class DtoName { }

[Readonly(typeof(User))]
public partial class ReadonlyUser { }

[Required(typeof(User))] // requires C# 11+
public partial class RequiredUser { }

[Union(typeof(User), typeof(Chat))]
public partial class UserChat { }

// Optional: disable generated empty ctor
[Pick(typeof(User), nameof(User.Id), nameof(User.Name), GenerateDefaultCtor = false)]
public partial class UserSummaryNoDefaultCtor { }

// using multiple attributes (GenerateDefaultCtor = false is required for all except one)
[Readonly(typeof(User))] 
[Omit(typeof(Chat), nameof(Chat.Id), GenerateDefaultCtor = false)]
public partial class ReadonlyUserWithChat { }

3. Use generated DTOs:

var summary = new UserSummaryNoDefaultCtor(user);
// var summary2 = new UserSummaryNoDefaultCtor(); // no parameterless ctor when GenerateDefaultCtor = false

Attribute behavior

• Pick: include only the listed fields/properties from the source type; generated ctor copies those members.
• Omit: include all eligible members except the listed ones.
• Readonly: include all eligible members with getters only.
• Required: include all public members and mark them required; emits an error if language version < C# 11.
• Union: merges members from multiple types; warns on duplicate names with same type, errors when types differ.

Common option (GenerateDefaultCtor) available on every attribute. Default is true. Set GenerateDefaultCtor = false to skip generating public DtoName() { }.

Eligible members are public/internal/protected-internal fields or properties that are non-static and not compiler-generated.

Sample project

• samples/DtoSrcGenSample demonstrates all attributes. Run dotnet build samples/DtoSrcGenSample to see generated output and basic usage.

Development notes

• Keep your consumer project language version at least 9; C# 11 is needed for RequiredAttribute.
• Diagnostics IDs: DSG3000 (missing member), DSG3001 (type mismatch in union), DSG2000 (duplicate union member), DSG2001 (internal members ignored), DSG3002 (Required unsupported language version).

Contributing

• Open issues or PRs with reproducible scenarios. Add samples that cover new behaviors.