custom apply config script

since nixos-rebuild does not support applying a built config (i.e. one
on which eval-config has already been called) without flakes.

I might or might not extend this into a more proper reimplementation of
nixos-rebuild.

3 files changed, 150 insertions, 0 deletions

diff --git a/pkgs/apply-config/apply-config b/pkgs/apply-config/apply-config
new file mode 100755
index 0000000..0ab7ff0
--- /dev/null
+++ b/pkgs/apply-config/apply-config
@@ -0,0 +1,134 @@
+#!/usr/bin/env gosh
+
+(use gauche.parseopt)
+(use gauche.process)
+(use util.match)
+
+(define action #f)
+(define attribute
+  (string-append "nixosConfigurations." (sys-gethostname)))
+(define keep #f)
+(define specialisation #f)
+(define verbose #f)
+(define extra-nix-args '())
+(define config-path ".")
+
+
+(define (usage progname)
+  (display
+#"~|progname|: Activate a nixos configuration.
+
+Usage:  ~|progname| [OPTIONS] [PATH] ACTION
+
+where ACTION is one of the actions which can be passed to switch-to-configuration
+(i.e. dry-activate, switch, test, or boot).
+
+Options:
+ -A --attr            Attribute which evaluates to a (built) configuration.
+                      Defaults to nixosConfigurations.<hostname>
+ -k --keep            Add a garbage collection root for the built configuration.
+ -s --specialisation  Specialisation to apply.
+ -v --verbose         Display commands before they are run.
+ -h --help            Print this help message.
+"))
+
+
+(define (run-command cmd)
+  (when verbose
+    (display cmd (standard-error-port)))
+  (do-process! cmd))
+
+(define (log-msg msg)
+  (display msg (standard-error-port)))
+
+(define (log-verbose msg)
+  (when verbose
+    (log-msg msg)))
+
+(define (main args)
+  (let-args
+   (cdr args)
+   ((o-verbose "v|verbose")
+    ; these are taken from nix-build
+    (o-attribute "A|attr=s")
+    (o-keep "k|keep")
+    (o-specialisation "s|specialisation=s")
+    (help "h|help" =>
+          (cut (begin (usage (car args)) (exit 0))))
+    (else (opt . _)
+          (print "unknown option: " opt "\n") (usage (car args)) (exit 1))
+    . restargs)
+
+   (when o-attribute
+     (set! attribute o-attribute))
+   (set! keep o-keep)
+   (set! specialisation o-specialisation)
+   (set! verbose o-verbose)
+
+   (match restargs
+     [((or "dry-activate" "switch" "test" "boot"))
+      (set! action (string->symbol (car restargs)))]
+     [(path (or "dry-activate" "switch" "test" "boot"))
+      (set! action (string->symbol (cadr restargs)))
+      (set! config-path path)]
+     [_ (begin (usage (car args)) (exit 1))])
+
+   (when (and specialisation (not (or (equal? action "test") (equal? action "switch"))))
+     (log-msg "Error: --specialisation can only be used with `test' or `switch'")
+     (exit 1))
+
+   (log-verbose (format "action: ~a" action))
+
+
+   (let ([built-config (build-config)])
+     (log-verbose (format "built config is ~a" built-config))
+     (install-in-env built-config)
+     (switch-to-configuration built-config))))
+
+
+(define (build-config)
+  (define (optional b args)
+    (if b args '()))
+  (define nix-cmd
+    (append
+     ; use nix-build since it actually prints the outpath
+     `(nix-build ,config-path --no-out-link --log-format bar-with-logs)
+     (optional attribute (list '-A (string-append attribute ".config.system.build.toplevel")))
+     extra-nix-args))
+  (log-verbose nix-cmd)
+  (process-output->string
+   nix-cmd :on-abnormal-exit :error))
+
+
+(define (install-in-env built-config)
+  (define cmd
+   '(nix-env -p /nix/var/nix/profiles/system --set ,built-config))
+
+  (if (or (equal? action 'switch) (equal? action 'boot))
+    (begin
+      (log-verbose cmd)
+      do-process! cmd)
+    (log-verbose
+     "skipping nix-env profile installation")))
+
+
+(define (switch-to-configuration built-config)
+  (define cmd
+    `(systemd-run
+      -E LOCALE_ARCHIVE
+      -E NIXOS_INSTALL_BOOTLOADER
+      --collect
+      ;; --no-ask-password
+      --pty
+      --quiet
+      --same-dir
+      --service-type=exec
+      --unit=nixos-rebuild-switch-to-configuration
+      --wait
+      ,(string-append built-config "/bin/switch-to-configuration")
+      ,action))
+
+  (log-verbose cmd)
+  (unless (do-process cmd)
+    (log "warning: error(s) occurred while switching to the new configuration")))
+
diff --git a/pkgs/apply-config/default.nix b/pkgs/apply-config/default.nix
new file mode 100644
index 0000000..03ba1f9
--- /dev/null
+++ b/pkgs/apply-config/default.nix
@@ -0,0 +1,14 @@
+{ stdenvNoCC, gauche }:
+
+stdenvNoCC.mkDerivation {
+  name = "apply-config";
+
+  src = ./.;
+
+  buildInputs = [ gauche ];
+
+  installPhase = ''
+    mkdir -p $out/bin
+    cp apply-config $out/bin
+  '';
+}
diff --git a/pkgs/overlay.nix b/pkgs/overlay.nix
index f7e4c5f..e3897c1 100644
--- a/pkgs/overlay.nix
+++ b/pkgs/overlay.nix
@@ -200,6 +200,8 @@ in
 
   nomsring = super.haskellPackages.callPackage ./nomsring {};
 
+  apply-config = self.callPackage ./apply-config {};
+
   #### sporadically maintained / updated ####
 
   hikari_unstable = (unstable.hikari.overrideAttrs (old: {