fix(204): add #nullable enabled directive on top of generated file

[tomflenner]

This PR

Adds #nullable enable directive at the top of the generated C# file to provide explicit nullable annotations context required by the compiler.

This resolves CS8669 compilation errors that occur when using the generated code in projects with <TreatWarningsAsErrors>true</TreatWarningsAsErrors> enabled.

Related Issues

Fixes #204

Notes

• The #nullable enable directive is added to the beginning of OpenFeature.g.cs
• This allows the generated code to compile successfully in projects that treat warnings as errors
• No changes to the actual generated code logic, only adds the required compiler directive

How to test

1. Create a C# project with <TreatWarningsAsErrors>true</TreatWarningsAsErrors> in the .csproj file
2. Generate C# code using the OpenFeature CLI code generator with this fix
3. Build the project
4. Verify that the CS8669 error no longer occurs
5. Alternatively, clone the reproduction repo at https://github.com/tomflenner/openfeature-cli-sharp-repro and test with the updated generator

[gemini-code-assist]

Summary of Changes

Hello @tomflenner, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request enhances the robustness of the C# code generation process by addressing a common compilation issue related to nullable reference types. By injecting the #nullable enable directive into the generated C# files, it ensures that projects with stringent warning-as-error configurations can seamlessly integrate the generated code without encountering build failures, thereby improving overall compatibility and developer experience.

Highlights

• Nullable Reference Types: The #nullable enable directive has been added to the top of all generated C# files. This explicitly enables nullable annotations context for the C# compiler.
• Compilation Error Resolution: This change resolves the CS8669 compilation error that occurs in C# projects where <TreatWarningsAsErrors>true</TreatWarningsAsErrors> is enabled, ensuring generated code compiles successfully under strict warning policies.
• Code Generation Template Update: The core change is implemented in the csharp.tmpl file, ensuring that all future C# code generated by the OpenFeature CLI will include the #nullable enable directive by default.

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[gemini-code-assist]

Code Review

This pull request adds the #nullable enable directive to the top of generated C# files to enable explicit nullable annotations. This resolves CS8669 compilation errors in projects with <TreatWarningsAsErrors>true enabled. The change is applied to the template and existing generated files.

[gemini-code-assist]

This directive enables nullable reference types in C#. It's good practice to include a comment explaining why this is necessary for maintainability.

Consider adding a brief comment to explain the purpose of this directive.

#nullable enable // Enable nullable reference types to ensure null-safety in generated code