I think this debate comes down to exactly what "reproducible" means. Nix doesn't give bit-exact reproducibility, but it does give reproducible
environments, by ensuring that the inputs are always bit-exact. It is closer to being fully reproducible than most other build systems (including Bazel) -- but because it can only reasonably ensure that the inputs are exact, it's still necessary for the build processes themselves to be fully deterministic to get end-to-end bit-exactness.
Nix on its own doesn't fully resolve supply chain concerns about binaries, but it can provide answers to a myriad of other problems. I think most people like Nix reproducibility, and it is marketed as such, for the sake of development: life is much easier when you know for sure you have the exact same version of each dependency, in the exact same configuration. A build on one machine may not be bit-exact to a build on another machine, but it will be exactly the same source code all the way down.
The quest to get every build process to be deterministic is definitely a bigger problem and it will never be solved for all of Nixpkgs. NixOS does have a reproducibility project[1], and some non-trivial amount of NixOS actually is properly reproducible, but the observation that Nixpkgs is too vast is definitely spot-on, especially because in most cases the real issues lie upstream. (and carrying patches for reproducibility is possible, but it adds even more maintainer burden.)
[1]: https://reproducible.nixos.org/
Nix on its own doesn't fully resolve supply chain concerns about binaries, but it can provide answers to a myriad of other problems. I think most people like Nix reproducibility, and it is marketed as such, for the sake of development: life is much easier when you know for sure you have the exact same version of each dependency, in the exact same configuration. A build on one machine may not be bit-exact to a build on another machine, but it will be exactly the same source code all the way down.
The quest to get every build process to be deterministic is definitely a bigger problem and it will never be solved for all of Nixpkgs. NixOS does have a reproducibility project[1], and some non-trivial amount of NixOS actually is properly reproducible, but the observation that Nixpkgs is too vast is definitely spot-on, especially because in most cases the real issues lie upstream. (and carrying patches for reproducibility is possible, but it adds even more maintainer burden.)
[1]: https://reproducible.nixos.org/