refactor: introduce nixos/default.nix

The system prompt addition is to make it run `npins show <pin>`
rather than `npins show` when looking for a specific pin.

`npins get-path` is mentioned because the model doesn't "know"
it yet (the subcommand was introduced in 2025 Dec).

1 files changed, 3 insertions, 35 deletions

diff --git a/nixos/rebuild b/nixos/rebuild
index 3c675b2..395f78d 100755
--- a/nixos/rebuild
+++ b/nixos/rebuild
@@ -3,49 +3,17 @@ set -euo pipefail
 
 top=$(dirname "$(realpath "$0")")
 hostDir="$top/hosts/$HOSTNAME"
-defaultConfigPath="$hostDir/default.nix"
-privateConfigPath="$hostDir/private.nix"
 
-case "${1:-}" in
-  --default)
-    configPath="$defaultConfigPath"
-    shift
-    ;;
-  *)
-    if [ -f "$privateConfigPath" ]; then
-      configPath="$privateConfigPath"
-    else
-      configPath="$defaultConfigPath"
-    fi
-    ;;
-esac
-
-if [ ! -f "$configPath" ]; then
-  echo "aborting: $configPath doesn't exist"
+if [ ! -d "$hostDir" ]; then
+  echo "aborting: host directory $hostDir doesn't exist"
   exit 1
 fi
 
-nixpkgsPath=$(
-  cd "$top" &&
-  nix-instantiate --eval --raw \
-    --argstr host "$HOSTNAME" \
-    --expr '
-      { host }:
-      let
-        toml = builtins.readFile ./hosts/${host}/metadata.toml;
-        channel = (builtins.fromTOML toml).channel;
-      in
-      (import ./npins).${channel}.outPath
-    '
-)
-
 (
   # The result symlink created in the current directory is registered as a root of the Nix
   # garbage collector, so it's important that we call nixos-rebuild from the host directory.
   # (nix-build has an --out-link option but that option cannot be set via nixos-rebuild).
   cd "$hostDir" &&
 
-  # nixos-rebuild always reads Nixpkgs from the NIX_PATH,
-  # so we need to set it explicitly to our pinned version
-  exec nixos-rebuild "$@" --file "$top/system.nix" -I nixpkgs="$nixpkgsPath" -I nixos-config="$configPath"
+  exec nixos-rebuild "$@" --file "$top/default.nix" --attr "configurations.$HOSTNAME"
 )