Like:

warning: Ignoring dynamic derivation /nix/store/8apg4x2xbcx83xc0p1jk1qdiihkmhjyg-hello-2.12.1.drv.drv^out while querying missing paths; not yet implemented
error: Building dynamic derivations in one shot is not yet implemented.

https://discourse.nixos.org/t/determinate-nix-3-0/61202/80

Pure eval doesn’t exist outside of flakes (unfortunately), that flag is more or less a broken promise.

I wonder what was meant by that? Does it mean that nix-build --pure-eval doesn't actually perform evaluation purely?

And it's not like it's that difficult to use, I've ran nix darwin using this script for a couple of months just fine

{ pkgs ? import <nixpkgs> { }
, writeShellScriptBin ? pkgs.writeScriptBin
, directory
, ...
}:
writeShellScriptBin "darwin-rebuild-npins" ''
  set -eo pipefail

  pushd ${directory} > /dev/null

  echo "building the system configuration..."
  system=$(nix-instantiate --eval --expr builtins.currentSystem | tr -d \")
  systemConfig=$(nix-build --pure-eval --no-out-link --argstr system $system --argstr name $(hostname) --expr "import (
    builtins.path {
      path = \"$(pwd)\";
      sha256 = \"$(nix-hash --type sha256 --base32 .)\";
    }
  )" | tee /dev/tty)

  profile=/nix/var/nix/profiles/system

  if [ "$USER" != root ] && [ ! -w $(dirname "$profile") ]; then
    sudo nix-env -p "$profile" --set "$systemConfig"
  else
    nix-env -p "$profile" --set "$systemConfig"
  fi

  "$systemConfig/activate-user"
  if [ "$USER" != root ]; then
    sudo "$systemConfig/activate"
  else
    "$systemConfig/activate"
  fi

  popd > /dev/null
''

In reply to @emilazy:matrix.org
a lot of things that user posts are wrong. you do have to copy your sources with pure eval though, which sort of reduces to being flakes in many ways people care about

Needing to copy sources is unfortunate, sure, but seeing as flakes also do that anyways, shouldn't matter much

And this approach doesn't require any changes to be done to the cppnix source code

In reply to @raitobezarius:matrix.org
lazy trees is exactly about removing that requirement

In reply to @weethet:catgirl.cloud

And it's not like it's that difficult to use, I've ran nix darwin using this script for a couple of months just fine

{ pkgs ? import <nixpkgs> { }
, writeShellScriptBin ? pkgs.writeScriptBin
, directory
, ...
}:
writeShellScriptBin "darwin-rebuild-npins" ''
  set -eo pipefail

  pushd ${directory} > /dev/null

  echo "building the system configuration..."
  system=$(nix-instantiate --eval --expr builtins.currentSystem | tr -d \")
  systemConfig=$(nix-build --pure-eval --no-out-link --argstr system $system --argstr name $(hostname) --expr "import (
    builtins.path {
      path = \"$(pwd)\";
      sha256 = \"$(nix-hash --type sha256 --base32 .)\";
    }
  )" | tee /dev/tty)

  profile=/nix/var/nix/profiles/system

  if [ "$USER" != root ] && [ ! -w $(dirname "$profile") ]; then
    sudo nix-env -p "$profile" --set "$systemConfig"
  else
    nix-env -p "$profile" --set "$systemConfig"
  fi

  "$systemConfig/activate-user"
  if [ "$USER" != root ]; then
    sudo "$systemConfig/activate"
  else
    "$systemConfig/activate"
  fi

  popd > /dev/null
''

In reply to @emilazy:matrix.org
there's also some talk that maybe some eval perf improvements only apply to flakes but not non-flakes pure eval, though I find that claim dubious without substantiation