`write-npins` fails on macOS due to GNU `mktemp` incompatibility

[anmayithap]

Issue: write-npins fails on macOS due to GNU mktemp incompatibility

Description

The write-npins script is currently broken on macOS (and other BSD-based systems) because it relies on the GNU-specific --suffix flag for mktemp. The native BSD mktemp utility on macOS does not recognize this option, causing the script to crash.

Error Output

mktemp: unrecognized option `--suffix=.nix'
usage: mktemp [-d] [-p tmpdir] [-q] [-t prefix] [-u] template ...
       mktemp [-d] [-p tmpdir] [-q] [-u] -t prefix

Root Cause

The script uses writeShellApplication but does not guarantee that the GNU version of mktemp (from coreutils) is used over the host's system path. On macOS, /usr/bin/mktemp (BSD) often takes precedence or is called instead of the Nix-provided one if not explicitly handled.

Expected Behavior

The script should be hermetic and use the GNU mktemp from the Nix store to ensure consistent behavior across all platforms (Linux/Darwin).

Suggested Fix

In the writeShellApplication definition for write-npins:

1. Ensure coreutils is present in runtimeInputs.
2. Hardcode the path to mktemp using ${coreutils}/bin/mktemp inside the script text to avoid picking up the host's BSD version.
3. Alternatively, use a portable mktemp syntax that works on both versions (e.g., mktemp /tmp/npins.XXXXXXXX.nix).

[anmayithap]

Workaround / Proposed Fix

I was able to fix this locally by overriding the derivation to use the absolute path to GNU mktemp. Since it's a writeShellApplication, patching the text attribute directly ensures the script is hermetic:

perSystem = {pkgs, ...}: let
  write-npins = config.packages.write-npins.overrideAttrs (_final: previous: {
    text = builtins.replaceStrings
      ["mktemp"]
      ["${pkgs.coreutils}/bin/mktemp"]
      previous.text;
    runtimeInputs = (previous.runtimeInputs or []) ++ [pkgs.coreutils];
  });
in {
  packages.write-npins = write-npins;
}