Caching nix shell build inputs: Difference between revisions

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Created page with "== Problem statement == Caching a Nix build is ''straightforward'' if there's a build result. We can use {{ic|nix-store --query --requisites}} to query the runtime closure of..."
 
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<syntaxhighlight lang="nix">
<syntaxhighlight lang="nix">
let nixpkgs = import <nixpkgs> {};
let pkgs = import <nixpkgs> {};
in
in
with nixpkgs;
with pkgs.stdenv;
with stdenv;
with pkgs.stdenv.lib;
with stdenv.lib;
pkgs.mkShell {
mkShell {
   name = "example-shell";
   name = "example-shell";
   buildInputs = [];
  nativeBuildInputs = with pkgs.buildPackages; [ /* tools */ ];
   buildInputs = with pkgs; [ /* libs */ ];
}
}
</syntaxhighlight>
</syntaxhighlight>
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== How can we cache all buildInputs for mkShell? ==
== How can we cache all buildInputs for mkShell? ==


A [https://fzakaria.com/2020/08/11/caching-your-nix-shell.html blog post] on the subject improved upon the previous wisdom and came up with the following
A [https://fzakaria.com/2020/08/11/caching-your-nix-shell.html blog post] ([https://web.archive.org/web/20201012134126/https://fzakaria.com/2020/08/11/caching-your-nix-shell.html mirror]) on the subject improved upon the previous wisdom and came up with the following


<syntaxhighlight lang="bash">
<syntaxhighlight lang="bash">
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nix-build shell.nix -A inputDerivation | cachix push $name
nix-build shell.nix -A inputDerivation | cachix push $name
</syntaxhighlight>
</syntaxhighlight>
[[Category:nix]]

Latest revision as of 19:55, 24 April 2024

Problem statement

Caching a Nix build is straightforward if there's a build result. We can use nix-store --query --requisites to query the runtime closure of the build for a binary distribution".

Unfortunately, this is not doable with mkShell as they are purposefully not build-able.

let pkgs = import <nixpkgs> {};
in
with pkgs.stdenv;
with pkgs.stdenv.lib;
pkgs.mkShell {
  name = "example-shell";
  nativeBuildInputs = with pkgs.buildPackages; [ /* tools */ ];
  buildInputs = with pkgs; [ /* libs */ ];
}
$ nix-build shell.nix

This derivation is not meant to be built, aborting

We could perform nix-store --query --requisites on the derivation nix-instantiate shell.nix however that results in a source transitive closure; which is unecessary if the goal is to simply cache buildInputs.

How can we cache all buildInputs for mkShell?

A blog post (mirror) on the subject improved upon the previous wisdom and came up with the following

nix-store --query --references $(nix-instantiate shell.nix) | \
    xargs nix-store --realise | \
    xargs nix-store --query --requisites | \
    cachix push your_cache

The "trick" here; is to rely on --references which gives only the immediate dependencies. For each dependency then it's runtime closure is calculated.

inputDerivation

A recent improvement to 'nixpkgs included the inputDerivation attribute. https://github.com/NixOS/nixpkgs/pull/95536

This further improves on the previous example by also supporting derivations with multiple outputs.

nix-build shell.nix -A inputDerivation

or if you are using cachix

nix-build shell.nix -A inputDerivation | cachix push $name