1 files changed, 28 insertions, 24 deletions
diff --git a/nixos/rebuild b/nixos/rebuild
index 80a52cd..9e62b33 100755
--- a/nixos/rebuild
+++ b/nixos/rebuild
@@ -1,31 +1,35 @@
 #!/usr/bin/env bash
 set -euo pipefail
 
-# Enable all future paths in this script to be relative to the directory containing the script.
-cd "$(dirname -- "${BASH_SOURCE[0]}")"
-
-configPath=$(realpath -- "hosts/$HOSTNAME/default.nix")
+top=$(dirname "$(realpath "$0")")
+configPath="$top/hosts/$HOSTNAME/default.nix"
 
 if [ ! -f $configPath ]; then
-    echo "aborting: $configPath doesn't exist"
-    exit 1
-fi
-
-firstLine=$(head -n1 "$configPath")
-
-if ! echo "$firstLine" | grep -E ^"# channel *=" > /dev/null; then
-    echo "aborting: $configPath doesn't start with \`# channel=\"...\"\`, where ... is a pin from sources.json"
-    exit 1
+  echo "aborting: $configPath doesn't exist"
+  exit 1
 fi
 
-nix-eval() {
-    nix-instantiate --eval --read-write-mode "$@" \
-      | tr -d \"  # nix-instantiate has no raw output yet (like the experimental nix eval)
-}
-
-channel=$(nix-eval --argstr line "$(echo $firstLine | tr -d \#)" --expr '{line}: (builtins.fromTOML line).channel')
-nixpkgsPath=$(nix-eval --argstr channel "$channel" --expr '{channel}: (import ./npins).${channel}.outPath')
-
-# nixos-rebuild always reads Nixpkgs from the NIX_PATH,
-# so we need to set it explicitly to our pinned version
-exec nixos-rebuild "$@" -I nixpkgs="$nixpkgsPath" -I nixos-config="$configPath" -I top="$(pwd)"
+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 $top/hosts/$HOSTNAME &&
+
+  # nixos-rebuild always reads Nixpkgs from the NIX_PATH,
+  # so we need to set it explicitly to our pinned version
+  exec nixos-rebuild "$@" -I nixpkgs="$nixpkgsPath" -I nixos-config="$configPath" -I top="$top"
+)