Nix-shell: How to run `corepack enable` to install modern Yarn?

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corepack enable modifies installation directories, which means it tries to write to /nix/store/...nodejs-x.y.z/bin/, but that’s not allowed.

It only creates some symlinks, so what you can do is package those symlinks:

stdenv.mkDerivation {
  name = "corepack-shims";
  buildInputs = [ nodejs-17_x ];
  phases = [ "installPhase" ];
  installPhase = ''
    mkdir -p $out/bin
    corepack enable --install-directory=$out/bin
  '';
}

You can then use that derivation as a build input for some other derivation, and the corepack shims will be available in $PATH.

Note that corepack downloads package managers to ~/.node/corepack, but $HOME is set to /homeless-shelter inside Nix builds. So when using the corepack shims, you may have to give it a writable home directory by doing something like: export HOME=$TMPDIR

EDIT: You can apparently also set COREPACK_HOME if you don’t want to modify HOME.

EDIT 2: Corepack downloading stuff also makes your build impure. Not sure what the best approach to using corepack is, really.

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