The Curse of NixOS

Re:The Curse of NixOS by mindslight on Monday January 24, 2022 @09:32AM (#30058019)

The semantics are simple and necessary, yes. The syntax is kind of crap in some ways (in others it's awesome and I wish other languages were as lightweight). Syntax in general is a bikeshed, but that doesn't mean we can't objectively critique things like having function definition being a mere ":". That one on its own is probably responsible for much of the indecipherability.

Also some of the higher level constructs really aren't clear (like overrideDerivation/overrideAttrs/override, I still don't fully get). And mkDefault/mkForce/etc could be a bit more front and center rather than in "lib".

Also every time I run nixos-rebuild and it takes several+ seconds to evaluate my Nix expression I've got to wonder how much the implementation being this cute functional fixpoint is holding performance back.

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Re:The Curse of NixOS by rnhmjoj on Tuesday January 25, 2022 @03:18AM (#30069486)

> overrideDerivation/overrideAttrs/override, I still don't fully get

Packages are implemented as functions that take dependencies as arguments, do some stuff and ultimately output the result of calling mkDerivation (i.e. a derivation).

`override` allows you to change the arguments of the package, while `overrideAttrs` allows you to change the arguments of mkDerivation: the implementation of the package itself. `overrideDerivation` is essentially a deprecated `overrideAttrs` version.

https://nixos.org/manual/nixpkgs/stable/#chap-overrides for a better explenation.

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Re:The Curse of NixOS by mindslight on Tuesday January 25, 2022 @10:48AM (#30073122)

Ah, I had forgotten `override` is easy. Rereading that page I still don't get the difference between `overrideAttrs` and `overrideDerivation`. `overrideAttrs` is newer and preferred, yet it doesn't spell out where you cannot use it and have to fall back to `overrideDeriviation`. And looking through my Nix code I've got various uses of `overrideDerivation`, which most likely means I tried `overrideAttrs` only to have it not work, so I tried the "deprecated" version and it did.

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Re:The Curse of NixOS by rnhmjoj on Tuesday January 25, 2022 @02:05PM (#30076416)

I think the manual is intetionally flying over `overrideDerivation` because it shouldn't be used. To understand the difference you'd have to know that `stdenv.mkDerivation` is a library function that wraps the Nix primitive `builtins.derivation`, which is what actually makes a derivation.

`overrideAttrs` changes the arguments of the former, while `overrideDerivation` changes the arguments of the latter. The reason is it's "deprecated" is that it forces a full evaluation of `stdenv.mkDerivation` before it can continue and it override the lower-level derivation, so some niceties that Nixpkgs provides don't work with it.

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Re:The Curse of NixOS by mindslight on Tuesday January 25, 2022 @05:10PM (#30078830)

Thank you for explaining the difference! I think the manual would be better served by an explanation like that, rather than just implying that `overrideDerivation` may still need to be used for some unspecified reason. I'll have to revisit my uses and see why `overrideAttr` didn't work for me. Perhaps I was using the wrong argument name.

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