Why can't I use let variables in flake.nix inputs?

[hexa]

See this post by infinisil on some caveats wrt flakes;

Experimental does not mean unstable: DetSys's perspective on Nix flakes

These are all Flakes deal-breakers for me: As you mention, the dependency explosion problem. Except that I disagree that the follows mechanism is a good solution for that. It’s a hack and can cause various breakages. We need a version resolver. And no, I will not use your proprietary third-party project to hack around that. Flakes doesn’t support passing arguments from the CLI. This is a clear downgrade from the stable commands. Eelco keeps saying that configurable derivations will address thi…

especially

@Infinisil

The flake.nix file not actually being a proper Nix file is a fundamental design flaw, it’s very inconsistent and leads to surprises, a clear downgrade from stable Nix.