Create and use a source generator

You can use source generators as an additional step in your script compilation process, to add new code while you compile your existing code. As with code analyzers, you can use existing source generators or create your own.

Note: Unity only supports version 6.0.0-preview of the System.Text.Json namespace. If you want to use this namespace in your application, ensure you use version 6.0.0-preview. For more information about System.Text.Json, refer to Microsoft’s System.Text.Json Namespace documentation.

To create a source generator in Visual Studio and then apply it for use in your Unity project:

1. In Visual Studio, create a C# class library project that targets .NET Standard 2.0 and name the project ExampleSourceGenerator.

2. Install the Microsoft.CodeAnalysis.Csharp NuGet package for the project. Your source generator must use Microsoft.CodeAnalysis.Csharp 4.3 to work with Unity.

3. In your Visual Studio project, create a new C# file and add the following code:

   using Microsoft.CodeAnalysis;
   using Microsoft.CodeAnalysis.Text;
   using System.Text;
   
   namespace ExampleSourceGenerator
   {
       [Generator]
       public class ExampleSourceGenerator : ISourceGenerator
       {
           public void Execute(GeneratorExecutionContext context)
           {
               System.Console.WriteLine(System.DateTime.Now.ToString());
   
               var sourceBuilder = new StringBuilder(
               @"
               using System;
               namespace ExampleSourceGenerated
               {
                   public static class ExampleSourceGenerated
                   {
                       public static string GetTestText()
                       {
                           return ""This is from source generator ");
   
               sourceBuilder.Append(System.DateTime.Now.ToString());
   
               sourceBuilder.Append(
                   @""";
                       }
       }
   }
   ");
   
               context.AddSource("exampleSourceGenerator", SourceText.From(sourceBuilder.ToString(), Encoding.UTF8));
           }
   
           public void Initialize(GeneratorInitializationContext context) { }
       }
   }
   

4. Build your source generator for release. To do this, go to Build and select the Batch Build option, then select the Release option and Build.

5. In your source generator’s project folder, find the bin/Release/netstandard2.0/ExampleSourceGenerator.dll file.

6. Copy this file into your Unity project, inside the Assets folder.

7. Inside the Asset Browser, click on the .dll file to open the Plugin Inspector window.

8. Under Select platforms for plugin, disable Any Platform.

9. Under Include Platforms, disable Editor and Standalone.

10. Under Asset Labels, click on the label icon to open the Asset labels sub-menu.

11. Create and assign a new label called RoslynAnalyzer. To do this, type RoslynAnalyzer in the text input field of the Asset labels sub-menu and press enter. This label must match exactly and is case sensitive. Once created, the label appears in the Asset labels sub-menu from then on. You can click on the name of the label in the menu to assign it to other analyzers.

12. To test the source generator is working, create a new MonoBehaviour script in the Editor with the following code:

    using UnityEngine;
    
    public class HelloFromSourceGenerator : MonoBehaviour
    {
        static string GetStringFromSourceGenerator()
        {
            return ExampleSourceGenerated.ExampleSourceGenerated.GetTestText();
        }
    
        // Start is called before the first frame update
        void Start()
        {
            var output = "Test";
            output = GetStringFromSourceGenerator();
            Debug.Log(output);
        }
    }
    

13. If the source generator is injected into more than one assembly, your IDE displays a compiler warning about conflicts (CS0436). To remove this warning, you can do one of the following:
    • Make the ExampleSourceGenerated class in the ExampleSourceGenerator example internal. Important: in this case you can only access the generated class from within the same assembly.
    • Change the name of the ExampleSourceGenerated class so that it’s unique to a given assembly, for example ExampleSourceGenerated_MyAssembly.

14. Add this script to a GameObject in the scene and enter Play mode. A message from the source generator appears in the Console window, including the time stamp.

For more information about source generators, refer to Microsoft’s Source Generators documentation.

Additional resources

• Install and use an existing analyzer or source generator