nixos-rebuild-ng: support using nix-output-monitor

nixos/modules/installer/tools/tools.nix

@@ -72,6 +72,7 @@ let
   nixos-rebuild-ng = pkgs.nixos-rebuild-ng.override {
     nix = config.nix.package;
     withNgSuffix = false;
+    withNom = config.system.rebuild.enableNom;
     withReexec = true;
   };
 
@@ -287,6 +288,14 @@ in
     '';
   };
 
+  options.system.rebuild.enableNom = lib.mkEnableOption "" // {
+    default = false;
+    description = ''
+      Whether to use ‘nix-output-monitor’ in place of ‘nix’ when rebuilding.
+      This produces a more aesthetically pleasing terminal experience.
+    '';
+  };
+
   imports =
     let
       mkToolModule =

nixos/tests/all-tests.nix

@@ -1059,6 +1059,7 @@ in
   nixos-rebuild-specialisations-ng = runTestOn [ "x86_64-linux" ] {
     imports = [ ./nixos-rebuild-specialisations.nix ];
     _module.args.withNg = true;
+    _module.args.withNom = true;
   };
   nixos-rebuild-target-host = runTest {
     imports = [ ./nixos-rebuild-target-host.nix ];

pkgs/by-name/ni/nix-output-monitor/package.nix

@@ -3,10 +3,24 @@
   haskellPackages,
   installShellFiles,
   lib,
+  nix,
+  replaceVars,
+
+  # Allow pinning a specific Nix version.
+  withPinnedNix ? false,
 }:
 let
   inherit (haskell.lib.compose) justStaticExecutables overrideCabal;
 
+  # If we're pinning Nix, then substitute with a Nix path; otherwise, just the name of the binary.
+  ambientOrPinned = name: if withPinnedNix then lib.getExe' nix name else name;
+
+  pinnedNixPatch = replaceVars ./pin-a-specific-nix.patch {
+    nix = ambientOrPinned "nix";
+    nix-build = ambientOrPinned "nix-build";
+    nix-shell = ambientOrPinned "nix-shell";
+  };
+
   overrides = {
     passthru.updateScript = ./update.sh;
 
@@ -15,13 +29,17 @@ let
     testTargets = [ "unit-tests" ];
 
     buildTools = [ installShellFiles ];
+
+    patches = [ pinnedNixPatch ];
+
     postInstall = ''
       ln -s nom "$out/bin/nom-build"
       ln -s nom "$out/bin/nom-shell"
       chmod a+x $out/bin/nom-build
       installShellCompletion completions/*
     '';
   };
+
   raw-pkg = haskellPackages.callPackage ./generated-package.nix { };
 in
 lib.pipe raw-pkg [

pkgs/by-name/ni/nix-output-monitor/pin-a-specific-nix.patch

@@ -0,0 +1,62 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Philip Taron <philip.taron@gmail.com>
+Date: Thu, 23 Oct 2025 10:32:59 -0700
+Subject: [PATCH] exe: allow pinning a specific Nix version
+
+---
+ exe/Main.hs | 22 +++++++++++-----------
+ 1 file changed, 11 insertions(+), 11 deletions(-)
+
+diff --git a/exe/Main.hs b/exe/Main.hs
+index 5e0f010..01b9e06 100644
+--- a/exe/Main.hs
++++ b/exe/Main.hs
+@@ -72,18 +72,18 @@ runApp :: String -> [String] -> IO Void
+ runApp = \cases
+   _ ["--version"] -> do
+     hPutStrLn stderr ("nix-output-monitor " <> fromString (showVersion version))
+-    exitWith =<< runProcess (proc "nix" ["--version"])
+-  "nom-build" args -> exitWith =<< runMonitoredCommand defaultConfig (proc "nix-build" (withJSON args))
++    exitWith =<< runProcess (proc "@nix@" ["--version"])
++  "nom-build" args -> exitWith =<< runMonitoredCommand defaultConfig (proc "@nix-build@" (withJSON args))
+   "nom-shell" args -> do
+-    exitOnFailure =<< runMonitoredCommand defaultConfig{silent = True} (proc "nix-shell" (withJSON args <> ["--run", "exit"]))
+-    exitWith =<< runProcess (proc "nix-shell" args)
+-  "nom" ("build" : args) -> exitWith =<< runMonitoredCommand defaultConfig (proc "nix" ("build" : withJSON args))
++    exitOnFailure =<< runMonitoredCommand defaultConfig{silent = True} (proc "@nix-shell@" (withJSON args <> ["--run", "exit"]))
++    exitWith =<< runProcess (proc "@nix-shell@" args)
++  "nom" ("build" : args) -> exitWith =<< runMonitoredCommand defaultConfig (proc "@nix@" ("build" : withJSON args))
+   "nom" ("shell" : args) -> do
+-    exitOnFailure =<< runMonitoredCommand defaultConfig{silent = True} (proc "nix" ("shell" : withJSON (replaceCommandWithExit args)))
+-    exitWith =<< runProcess (proc "nix" ("shell" : args))
++    exitOnFailure =<< runMonitoredCommand defaultConfig{silent = True} (proc "@nix@" ("shell" : withJSON (replaceCommandWithExit args)))
++    exitWith =<< runProcess (proc "@nix@" ("shell" : args))
+   "nom" ("develop" : args) -> do
+-    exitOnFailure =<< runMonitoredCommand defaultConfig{silent = True} (proc "nix" ("develop" : withJSON (replaceCommandWithExit args)))
+-    exitWith =<< runProcess (proc "nix" ("develop" : args))
++    exitOnFailure =<< runMonitoredCommand defaultConfig{silent = True} (proc "@nix@" ("develop" : withJSON (replaceCommandWithExit args)))
++    exitWith =<< runProcess (proc "@nix@" ("develop" : args))
+   "nom" [] -> do
+     finalState <- monitorHandle @OldStyleInput defaultConfig{piping = True} stdin
+     if CMap.size finalState.fullSummary.failedBuilds + length finalState.nixErrors == 0
+@@ -108,7 +108,7 @@ printNixCompletion = \cases
+     exitSuccess
+   "nom" args@(sub_cmd : _)
+     | sub_cmd `elem` knownSubCommands ->
+-        exitWith =<< Process.runProcess (Process.proc "nix" args)
++        exitWith =<< Process.runProcess (Process.proc "@nix@" args)
+   prog args -> do
+     putTextLn $ "No completion support for " <> unwords (toText <$> prog : args)
+     exitFailure
+@@ -170,7 +170,7 @@ monitorHandle config input_handle = withParser @a \streamParser -> do
+       Terminal.hHideCursor outputHandle
+       hSetBuffering stdout (BlockBuffering (Just 1_000_000))
+
+-      current_system <- Exception.handle ((Nothing <$) . printIOException) $ Just . decodeUtf8 <$> Process.readProcessStdout_ (Process.proc "nix" ["eval", "--extra-experimental-features", "nix-command", "--impure", "--raw", "--expr", "builtins.currentSystem"])
++      current_system <- Exception.handle ((Nothing <$) . printIOException) $ Just . decodeUtf8 <$> Process.readProcessStdout_ (Process.proc "@nix@" ["eval", "--extra-experimental-features", "nix-command", "--impure", "--raw", "--expr", "builtins.currentSystem"])
+       first_state <- initalStateFromBuildPlatform current_system
+       -- We enforce here, that the state type is completely strict so that we don‘t accumulate thunks while running the program.
+       let first_process_state = MkProcessState (StrictType.Strict $ firstState @a first_state) (stateToText config first_state)
+-- 
+2.51.0
+

pkgs/by-name/ni/nixos-rebuild-ng/0001-replacements.patch

@@ -0,0 +1,62 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Philip Taron <philip.taron@gmail.com>
+Date: Wed, 22 Oct 2025 17:02:15 -0700
+Subject: [PATCH] nixos-rebuild-ng: patch out actual replacements
+
+Produced with `git format-patch -1 --zero-commit --stdout --relative=pkgs/by-name/ni/nixos-rebuild-ng/src HEAD^1`
+---
+ nixos_rebuild/constants.py | 18 +++++++++---------
+ pyproject.toml             |  6 +++---
+ 2 files changed, 12 insertions(+), 12 deletions(-)
+
+diff --git a/nixos_rebuild/constants.py b/nixos_rebuild/constants.py
+index f79922ea5c87..ee4fc0c49373 100644
+--- a/nixos_rebuild/constants.py
++++ b/nixos_rebuild/constants.py
+@@ -2,15 +2,15 @@ from typing import Final
+
+ # The name of this executable, for purposes of replacing `nixos-rebuild`.
+ # The derivation replaces this using a patch file.
+-EXECUTABLE: Final[str] = "nixos-rebuild-ng"
++EXECUTABLE: Final[str] = "@executable@"
+
+ # These names are replaced with absolute paths to Nix in the store in the derivation.
+ # Some of these names could be either `nix` or `nom`, and are called out as such.
+-NIX: Final[str] = "nix"
+-NIX_OR_NOM: Final[str] = "nix"
+-NIX_BUILD: Final[str] = "nix-build"
+-NIX_CHANNEL: Final[str] = "nix-channel"
+-NIX_COPY_CLOSURE: Final[str] = "nix-copy-closure"
+-NIX_ENV: Final[str] = "nix-env"
+-NIX_INSTANTIATE: Final[str] = "nix-instantiate"
+-NIX_STORE: Final[str] = "nix-store"
++NIX: Final[str] = "@nix@"
++NIX_OR_NOM: Final[str] = "@nix-or-nom@"
++NIX_BUILD: Final[str] = "@nix-build@"
++NIX_CHANNEL: Final[str] = "@nix-channel@"
++NIX_COPY_CLOSURE: Final[str] = "@nix-copy-closure@"
++NIX_ENV: Final[str] = "@nix-env@"
++NIX_INSTANTIATE: Final[str] = "@nix-instantiate@"
++NIX_STORE: Final[str] = "@nix-store@"
+diff --git a/pyproject.toml b/pyproject.toml
+index 757067db9f06..68dfa825a824 100644
+--- a/pyproject.toml
++++ b/pyproject.toml
+@@ -3,11 +3,11 @@ requires = ["setuptools"]
+ build-backend = "setuptools.build_meta"
+
+ [project]
+-name = "nixos-rebuild"
+-version = "0.0.0"
++name = "@executable@"
++version = "@version@"
+
+ [project.scripts]
+-nixos-rebuild = "nixos_rebuild:main"
++@executable@ = "nixos_rebuild:main"
+
+ [tool.setuptools.package-data]
+ nixos_rebuild = ["*.nix.template"]
+-- 
+2.51.0
+

pkgs/by-name/ni/nixos-rebuild-ng/0002-help-runs-man.patch

@@ -0,0 +1,30 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Philip Taron <philip.taron@gmail.com>
+Date: Thu, 23 Oct 2025 05:46:07 -0700
+Subject: [PATCH] nixos-rebuild-ng: patch out print_help to use the man page
+
+Produced with `git format-patch -1 --zero-commit --stdout --relative=pkgs/by-name/ni/nixos-rebuild-ng/src`
+---
+ nixos_rebuild/help.py | 7 +++++--
+ 1 file changed, 5 insertions(+), 2 deletions(-)
+
+diff --git a/nixos_rebuild/help.py b/nixos_rebuild/help.py
+index 7437550a37b8..dcb730e09ced 100644
+--- a/nixos_rebuild/help.py
++++ b/nixos_rebuild/help.py
+@@ -1,7 +1,10 @@
+ import argparse
++from subprocess import run
+ from typing import NoReturn
+
++from .constants import EXECUTABLE
++
+
+ def print_help(parser: argparse.ArgumentParser) -> NoReturn:
+-    parser.print_help()
+-    parser.exit()
++    r = run(["man", "8", EXECUTABLE], check=False)
++    parser.exit(r.returncode)
+-- 
+2.51.0
+