CodegenCS is a Toolkit for doing Code Generation using plain C#.

Before anything else, don't forget to read the Main Project Page to learn the basics (basic idea, basic features, and major components).

This page is only about CodegenCS Source Generator:

Our Source Generator allows running templates on-the-fly during compilation. We abstract the boilerplate and the hard parts of creating a source generator so you can only focus on your templates.

It's possible to render physical files on disk or just render in-memory (no need to add to source-control or put into ignore lists).

1. Install nuget CodegenCS.SourceGenerator to your project

   <ItemGroup>
     <PackageReference Include="CodegenCS.SourceGenerator" Version="3.5.2" />
   </ItemGroup>

2. Create a CodegenCS template. Example:

    class Template
    {
        void Main(ICodegenContext context)
        {
            context[$"MyClass1.g.cs"].Write($$"""
                public class MyClas1
                {
                }
                """);
        }
    }

3. Add this to your csproj:

    <ItemGroup>
      <CompilerVisibleItemMetadata Include="AdditionalFiles" MetadataName="CodegenCSOutput" />
      <AdditionalFiles Include="Template.csx" CodegenCSOutput="Memory" />
      <!-- Use "Memory" or "File", where "File" will save the output files to disk -->
      <!-- you can include as many templates as you want -->
    </ItemGroup>

4. If you want to augment on existing classes (using Roslyn Syntax Tree), just inject GeneratorExecutionContext like the example below: .

       void Main(ICodegenContext context, GeneratorExecutionContext generatorContext)
       {
           var classes = generatorContext.Compilation.SyntaxTrees
               .SelectMany(syntaxTree => syntaxTree.GetRoot().DescendantNodes())
               .Where(x => x is ClassDeclarationSyntax)
               .Cast<ClassDeclarationSyntax>()
               //.Where(c => c.Identifier.ValueText.EndsWith("Controller", StringComparison.OrdinalIgnoreCase)) // just an example
               .ToList();
   
           foreach (var c in classes)
           {
               var typeSymbol = generatorContext.Compilation.GetSemanticModel(c.SyntaxTree).GetDeclaredSymbol(c);
               var fqn = typeSymbol.ToDisplayString(SymbolDisplayFormat.FullyQualifiedFormat);
               if (fqn.StartsWith("global::"))
                   fqn = fqn.Substring("global::".Length);
               int pos = fqn.LastIndexOf(".");
               if (pos == -1)
                   continue;
               var className = fqn.Substring(pos + 1);
               var ns = fqn.Substring(0, pos);
               if (string.IsNullOrEmpty(className))
                   continue;
               context[$"{className}.g.cs"].Write(GenerateClass(ns, className));
           }
       }

   See full example here.