nixos-rebuild-ng: add repl

pkgs/by-name/ni/nixos-rebuild-ng/README.md

@@ -126,7 +126,7 @@ ruff format .
 - [ ] Change module system to allow easier opt-in, like
   `system.switch.enableNg` for `switch-to-configuration-ng`
 - [ ] Improve documentation
-- [ ] `nixos-rebuild repl` (calling old `nixos-rebuild` for now)
+- [x] `nixos-rebuild repl`
 - [ ] `nix` build/bootstrap
 - [ ] Generate tab completion via [`shtab`](https://docs.iterative.ai/shtab/)
 - [x] Reduce build closure

pkgs/by-name/ni/nixos-rebuild-ng/package.nix

@@ -39,11 +39,6 @@ python3Packages.buildPythonApplication rec {
     nix
   ];
 
-  preBuild = ''
-    substituteInPlace nixos_rebuild/__init__.py \
-      --subst-var-by nixos_rebuild ${lib.getExe nixos-rebuild}
-  '';
-
   postInstall =
     ''
       installManPage ${nixos-rebuild}/share/man/man8/nixos-rebuild.8

pkgs/by-name/ni/nixos-rebuild-ng/src/nixos_rebuild/__init__.py

@@ -1,7 +1,6 @@
 import argparse
 import atexit
 import json
-import os
 import sys
 from pathlib import Path
 from subprocess import run

pkgs/by-name/ni/nixos-rebuild-ng/src/nixos_rebuild/nix.py

@@ -1,6 +1,8 @@
 import os
 from datetime import datetime
+from importlib.resources import files
 from pathlib import Path
+from string import Template
 from subprocess import PIPE, CalledProcessError
 from typing import Final
 
@@ -18,6 +20,7 @@ from .process import run_wrapper
 from .utils import Args, dict_to_flags, info
 
 FLAKE_FLAGS: Final = ["--extra-experimental-features", "nix-command flakes"]
+FLAKE_REPL_TEMPLATE: Final = "repl.template.nix"
 
 
 def copy_closure(
@@ -279,6 +282,41 @@ def nixos_build_flake(
     return Path(r.stdout.strip())
 
 
+def repl(attr: str, build_attr: BuildAttr | None, **nix_flags: Args) -> None:
+    run_args: list[str | Path] = ["nix", "repl", "--file"]
+    if build_attr:
+        run_args.append(build_attr.path)
+        if build_attr.attr:
+            run_args.append(build_attr.attr)
+        run_wrapper([*run_args, *dict_to_flags(nix_flags)])
+    else:
+        run_wrapper([*run_args, "<nixpkgs/nixos>", *dict_to_flags(nix_flags)])
+
+
+def repl_flake(attr: str, flake: Flake, **flake_flags: Args) -> None:
+    expr = Template(
+        files(__package__).joinpath(FLAKE_REPL_TEMPLATE).read_text()
+    ).substitute(
+        flake_path=flake.path,
+        flake_attr=flake.attr,
+        bold="\033[1m",
+        blue="\033[34;1m",
+        attention="\033[35;1m",
+        reset="\033[0m",
+    )
+    run_wrapper(
+        [
+            "nix",
+            *FLAKE_FLAGS,
+            "repl",
+            "--impure",
+            "--expr",
+            expr,
+            *dict_to_flags(flake_flags),
+        ]
+    )
+
+
 def rollback(profile: Profile, target_host: Remote | None, sudo: bool) -> Path:
     "Rollback Nix profile, like one created by `nixos-rebuild switch`."
     run_wrapper(

pkgs/by-name/ni/nixos-rebuild-ng/src/nixos_rebuild/repl.template.nix

@@ -0,0 +1,40 @@
+let
+  flake = builtins.getFlake ''${flake_path}'';
+  configuration = flake.${flake_attr};
+  motd = ''
+    $${"\n"}
+    Hello and welcome to the NixOS configuration
+        ${flake_attr}
+        in ${flake_path}
+
+    The following is loaded into nix repl's scope:
+
+        - ${blue}config${reset}   All option values
+        - ${blue}options${reset}  Option data and metadata
+        - ${blue}pkgs${reset}     Nixpkgs package set
+        - ${blue}lib${reset}      Nixpkgs library functions
+        - other module arguments
+
+        - ${blue}flake${reset}    Flake outputs, inputs and source info of ${flake_path}
+
+    Use tab completion to browse around ${blue}config${reset}.
+
+    Use ${bold}:r${reset} to ${bold}reload${reset} everything after making a change in the flake.
+      (assuming ${flake_path} is a mutable flake ref)
+
+    See ${bold}:?${reset} for more repl commands.
+
+    ${attention}warning:${reset} nixos-rebuild repl does not currently enforce pure evaluation.
+  '';
+  scope =
+    assert configuration._type or null == ''configuration'';
+    assert configuration.class or ''nixos'' == ''nixos'';
+    configuration._module.args
+    // configuration._module.specialArgs
+    // {
+      inherit (configuration) config options;
+      lib = configuration.lib or configuration.pkgs.lib;
+      inherit flake;
+    };
+in
+builtins.seq scope builtins.trace motd scope

pkgs/by-name/ni/nixos-rebuild-ng/src/pyproject.toml

@@ -9,6 +9,9 @@ version = "0.0.0"
 [project.scripts]
 nixos-rebuild = "nixos_rebuild:main"
 
+[tool.setuptools.package-data]
+nixos_rebuild = ["*.template.nix"]
+
 [tool.mypy]
 # `--strict` config, but explicit options to avoid breaking build when mypy is
 # updated

pkgs/by-name/ni/nixos-rebuild-ng/src/tests/test_models.py

@@ -17,9 +17,7 @@ def test_building_attr_from_arg() -> None:
     assert m.BuildAttr.from_arg("attr", "file.nix") == m.BuildAttr(
         Path("file.nix"), "attr"
     )
-    assert m.BuildAttr.from_arg(None, "file.nix") == m.BuildAttr(
-        Path("file.nix"), None
-    )
+    assert m.BuildAttr.from_arg(None, "file.nix") == m.BuildAttr(Path("file.nix"), None)
 
 
 def test_flake_parse() -> None:

pkgs/by-name/ni/nixos-rebuild-ng/src/tests/test_nix.py

@@ -248,6 +248,25 @@ def test_nixos_build(mock_run: Any, monkeypatch: Any) -> None:
     )
 
 
+@patch(get_qualified_name(n.run_wrapper, n), autospec=True)
+def test_repl(mock_run: Any) -> None:
+    n.repl("attr", None, nix_flag=True)
+    mock_run.assert_called_with(
+        ["nix", "repl", "--file", "<nixpkgs/nixos>", "--nix-flag"]
+    )
+
+    n.repl("attr", m.BuildAttr(Path("file.nix"), "myAttr"))
+    mock_run.assert_called_with(["nix", "repl", "--file", Path("file.nix"), "myAttr"])
+
+
+@patch(get_qualified_name(n.run_wrapper, n), autospec=True)
+def test_repl_flake(mock_run: Any) -> None:
+    n.repl_flake("attr", m.Flake(Path("flake.nix"), "myAttr"), nix_flag=True)
+    # This method would be really annoying to test, and it is not that important
+    # So just check that we are at least calling it
+    assert mock_run.called
+
+
 @patch(get_qualified_name(n.run_wrapper, n), autospec=True)
 def test_rollback(mock_run: Any, tmp_path: Path) -> None:
     path = tmp_path / "test"