Add integration for C# using a custom .NET Source Generator for flag calls

Summary

Propose adding a new integration for C# to the CLI that leverages a custom .NET Source Generator. This generator will automatically create code for feature flag calls, streamlining flag management and usage in C# projects. We would keep the current csharp generation in the CLI but adding a new one for the source generators.

Motivation

• Enable seamless integration of OpenFeature in C# projects by automating the generation of flag call code.
• Reduce boilerplate and potential errors in flag usage.
• Improve developer productivity and code maintainability.

Approach

• Design and implement a custom .NET Source Generator that can parse feature flag definitions and generate corresponding C# code for flag calls.
• Integrate this workflow into the OpenFeature CLI so C# developers can easily set up and use this functionality.
• Provide documentation and usage examples for the new integration.

Tasks

• Research .NET Source Generators and their integration points with OpenFeature.
• Define the input format and configuration for flag definitions. I suggest using Attributes.
• Implement the source generator logic.
• Update the CLI to support C# integration using the generator.
• Write documentation and sample usage code.

Additional Context

This enhancement would provide first-class support for C# developers using OpenFeature, leveraging modern .NET tooling to make flag usage safer and more efficient.

Example of generated code by CLI

using OpenFeature.Extensions.SourceGenerator;

[FeatureFlag]
private bool IsEnabled;

By leveraging source generators for the C# implementation, it would give more flexibility because anyone could potentially make use of it, even without using the CLI.

Notes

More info: https://devblogs.microsoft.com/dotnet/introducing-c-source-generators/

Start by reviewing the CLI's existing C# generation and the linked .NET Source Generators material. Define the attribute-based flag input and integration points before implementing the generator and CLI support. Done includes working generated C# calls, documentation, and sample usage.