refactor: enable host-specific configuration

5 files changed, 33 insertions, 11 deletions

diff --git a/nixos/README.md b/nixos/README.md
index 6c4bcb1..1a9c50e 100644
--- a/nixos/README.md
+++ b/nixos/README.md
@@ -31,10 +31,13 @@ We're assuming that you just installed NixOS by going through the [official inst
      ```
      nixos-generate-config --dir .
      ```
-3. Pin Nixpkgs to the [latest stable version](https://nixos.org/manual/nixos/stable/release-notes) using npins:
+3. Rename the files to `$host-configuration.nix` and `$host-hardware-configuration.nix` where `$host` is the configured hostname.
+   Add `# channel="..."` to the start of the `$host-configuration.nix` file where `...` is the key of a channel pinned in `npins/sources.json`.
+   A new channel can be pinned with:
+
    ```
    nix-shell -p npins --run \
-     'npins init --bare && npins add --name nixos channel nixos-23.11'
+     'npins add --name nixos channel nixos-23.11'
    ```
 4. Remove all stateful channels:
    ```
@@ -42,7 +45,7 @@ We're assuming that you just installed NixOS by going through the [official inst
    ```
 5. Rebuild:
    ```
-   sudo ./rebuild switch
+   sudo HOSTNAME=$host ./rebuild switch
    ```
 6. Log out and back in again.
 
diff --git a/nixos/configuration.nix b/nixos/hamac-configuration.nix
index 7d785ab..306260d 100644
--- a/nixos/configuration.nix
+++ b/nixos/hamac-configuration.nix
@@ -1,10 +1,11 @@
+# channel="nixos"
 # See the configuration.nix(5) man page and the NixOS manual (accessible by running `nixos-help`).
 
 { config, pkgs, ... }:
 
 {
   imports = [
-    ./hardware-configuration.nix
+    ./hamac-hardware-configuration.nix
     ./sanix.nix
   ];
 
@@ -12,7 +13,7 @@
   boot.loader.systemd-boot.enable = true;
   boot.loader.efi.canTouchEfiVariables = true;
 
-  networking.hostName = "nixos"; # Define your hostname.
+  networking.hostName = "hamac";
 
   networking.networkmanager.enable = true;
 
diff --git a/nixos/hardware-configuration.nix b/nixos/hamac-hardware-configuration.nix
index 54b9d60..54b9d60 100644
--- a/nixos/hardware-configuration.nix
+++ b/nixos/hamac-hardware-configuration.nix
diff --git a/nixos/nixpkgs/path.nix b/nixos/nixpkgs/path.nix
deleted file mode 100644
index 7ae177e..0000000
--- a/nixos/nixpkgs/path.nix
+++ /dev/null
@@ -1,2 +0,0 @@
-# The Nixpkgs path to use
-(import ../npins).nixos.outPath
diff --git a/nixos/rebuild b/nixos/rebuild
index 98101c1..3cb086e 100755
--- a/nixos/rebuild
+++ b/nixos/rebuild
@@ -1,10 +1,30 @@
 #!/usr/bin/env bash
 set -euo pipefail
 
-# nix-instantiate --eval has no raw mode yet
-nixpkgsPath=$(nix-instantiate --eval --read-write-mode nixpkgs/path.nix | tr -d \")
-# Get the ./configuration.nix relative to this script
-configPath=$(realpath -- "$(dirname -- "${BASH_SOURCE[0]}")/configuration.nix")
+# Enable all future paths in this script to be relative to the directory containing the script.
+cd "$(dirname -- "${BASH_SOURCE[0]}")"
+
+configPath=$(realpath -- "$HOSTNAME-configuration.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: $configPath doesn't start with \`# channel=\"...\"\`, where ... is a pin from sources.json"
+    exit 1
+fi
+
+nix-eval() {
+    nix-instantiate --eval --read-write-mode "$@" \
+      | 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