In-repository file generation flake-parts module

As Nix users, we naturally want the source of all truth to reside within Nix files 📜 and other files that include that truth to be generated ⚡.

For example, who didn't want to dynamically include various facts about their project in the readme and make sure those are up-to-date?

but

1. project repositories are expected to include tracked readmes 📄

2. Git tracked or not, .gitignore files must sometimes exist 🤷

3. .github/workflows/* must be Git tracked (don't get me started on these)

4. and the list goes on

You may be thinking

Wait 🤔, so what if they must be tracked—I can still generate them from Nix and then check that my repository is clean.

And you'd be right! ...except that checking that your repository is clean cannot be a flake check.

Okay, so I'll make a flake check for each generated file.

Well, yes, you could. ...or you could use this project—if you're using flake-parts, that is (sorry).