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Comment by amarshall | Hacker News Reader

> I haven't found a clear list of packages that were going to be updated.

The ideal here, IMO, is to use flakes and the nix-diff to compare the build before switching. E.g.

    nixos-rebuild --flake '.#myhost' build
    nix-diff /nix/var/nix/profiles/system result
    sudo nixos-rebuild --flake '.#myhost' switch

Could do the same without flakes after the fact by running nix-diff on different generations in /nix/var/nix/profiles (there may be a way before switch). It’s unfortunate that how to do the above is non-obvious.

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There's nothing there that needs flakes (an experimental feature which people should not enable without understanding the implications). You could build a system derivation and run a diff against /run/current-system on it.

For what it's worth, nix-diff has very verbose output (it literally diffs everything that is different in the inputs & outputs). A slightly nicer way to diff systems is nvd[0] (example output[1]) which only shows version changes and added/removed packages.

[0]: https://gitlab.com/khumba/nvd

[1]: https://deploys.tvl.fyi/diff/4xmyvkr9nw0cwkn5q38p0cfc58x3jdy...

> experimental

Haven't flakes been non-experimental since 2.4?

No, using flakes still requires enabling the “experimental feature”. The difference in 2.4 is that you no longer need to use a prerelease version of Nix to have the experimental feature available.

Flakes are "experimental" in the sense that gmail was in "beta" for however many years. I feel like it's important to mention that you're attempting to rewrite nix[1] and explicitly ignoring flakes[2]. Many people using nix are coming to the conclusion that flakes make things much easier to use and understand, and they obviate the need for a lot of secondary tooling that has become standard. There's an easy way to gauge support for flakes: look at how many high-profile nix repos have an up-to-date flakes.nix file.

[1] https://tvl.fyi/blog/rewriting-nix

[2] https://lobste.rs/s/ypwgwp/tvix_we_are_rewriting_nix#c_zvtze...

I was using flakes, yes. I remember seeing nix-diff, but most of the time nixos-rebuild dry-build was enough. Sometimes dry build was failing with error, but switching or activating it ran without errors. Never figured out what was wrong :(

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