Add --option NAME VALUE: generic Nix configuration passthrough

README.md

@@ -267,6 +267,18 @@ As an alternative, one can also specify remote builder as usual in
 `/etc/nix/machines` or via the `nix.buildMachines` nixos options in
 `configuration.nix`. This allows to parallelize builds across multiple machines.
 
+## Setting arbitrary Nix options
+
+Use `--option NAME VALUE` to pass any Nix configuration setting through to every
+`nix`/`nix-env` invocation nixpkgs-review makes, the same way `nix --option`
+works. It can be given multiple times:
+
+```console
+$ nixpkgs-review pr --option cores 4 --option sandbox false 37244
+```
+
+See `man nix.conf` for the full list of available settings.
+
 ## Cross compile, static, cuda
 
 If you want to cross compile you can do that with the `--pkgs=` flag:

nixpkgs_review/cli/__init__.py

@@ -321,6 +321,18 @@ def common_flags() -> list[CommonFlag]:
             default=None,
             help="Alternative package set to use for building, e.g. pkgsMusl, pkgsStatic, or pkgsCross.aarch64-multiplatform",
         ),
+        CommonFlag(
+            "--option",
+            dest="option",
+            type=str,
+            nargs=2,
+            metavar=("NAME", "VALUE"),
+            action="append",
+            default=[],
+            help="Set a Nix configuration option, e.g. --option cores 4 "
+            "(can be passed multiple times). Passed through as-is to every "
+            "nix/nix-env invocation; see `man nix.conf` for available settings",
+        ),
     ]
 
 

nixpkgs_review/nix.py

@@ -29,6 +29,7 @@ class BuildConfig:
     num_eval_workers: int = 1
     max_memory_size: int = 4096
     pkgs: str | None = None
+    options: tuple[tuple[str, str], ...] = ()
 
 
 @dataclass
@@ -86,7 +87,18 @@ def serialize(self) -> dict:
 REVIEW_SHELL: Final[str] = str(ROOT.joinpath("nix/review-shell.nix"))
 
 
-def _nix_common_flags(allow: AllowedFeatures, nix_path: str) -> list[str]:
+def _option_flags(options: tuple[tuple[str, str], ...]) -> list[str]:
+    flags: list[str] = []
+    for name, value in options:
+        flags += ["--option", name, value]
+    return flags
+
+
+def _nix_common_flags(
+    allow: AllowedFeatures,
+    nix_path: str,
+    options: tuple[tuple[str, str], ...] = (),
+) -> list[str]:
     return [
         "--extra-experimental-features",
         "nix-command",
@@ -96,6 +108,7 @@ def _nix_common_flags(allow: AllowedFeatures, nix_path: str) -> list[str]:
         "--allow-import-from-derivation"
         if allow.ifd
         else "--no-allow-import-from-derivation",
+        *_option_flags(options),
     ]
 
 
@@ -112,6 +125,7 @@ class ShellConfig:
     run: str | None = None
     sandbox: bool = False
     pkgs: str | None = None
+    options: tuple[tuple[str, str], ...] = ()
 
 
 def nix_shell(
@@ -145,6 +159,7 @@ def nix_shell(
             *shell_file_args,
             "--nix-path",
             config.nix_path,
+            *_option_flags(config.options),
             REVIEW_SHELL,
         ]
         if config.run:
@@ -240,6 +255,7 @@ def tmpfs(path: Path | str, *, is_dir: bool = True) -> list[str]:
         *shell_file_args,
         "--nix-path",
         config.nix_path,
+        *_option_flags(config.options),
         REVIEW_SHELL,
     ]
 
@@ -327,7 +343,9 @@ def multi_system_eval(
             "--max-memory-size",
             str(build_config.max_memory_size),
             "--no-instantiate",
-            *_nix_common_flags(build_config.allow, build_config.nix_path),
+            *_nix_common_flags(
+                build_config.allow, build_config.nix_path, build_config.options
+            ),
             "--expr",
             f"(import {eval_script} {{ attr-json = {attr_json.name}; }})",
             "--apply",
@@ -399,7 +417,9 @@ def nix_build(
         "build",
         "--file",
         REVIEW_SHELL,
-        *_nix_common_flags(build_config.allow, build_config.nix_path),
+        *_nix_common_flags(
+            build_config.allow, build_config.nix_path, build_config.options
+        ),
         "--no-link",
         "--keep-going",
     ]
@@ -424,6 +444,7 @@ def nix_build(
         shell_file_args=shell_file_args,
         allow=build_config.allow,
         nix_path=build_config.nix_path,
+        options=build_config.options,
     )
 
     command += shell_file_args + shlex.split(args)
@@ -471,12 +492,13 @@ def _write_review_shell_drv(
     shell_file_args: list[str],
     allow: AllowedFeatures,
     nix_path: str,
+    options: tuple[tuple[str, str], ...] = (),
 ) -> None:
     review_drv_link: Path = cache_directory / "review-shell.drv"
 
     cmd: list[str] = [
         "nix-instantiate",
-        *_nix_common_flags(allow, nix_path),
+        *_nix_common_flags(allow, nix_path, options),
         *shell_file_args,
         REVIEW_SHELL,
     ]

nixpkgs_review/review.py

@@ -420,6 +420,7 @@ def build_commit(
             self.systems,
             self.build_config.allow,
             self.build_config.pkgs,
+            self.build_config.options,
         )
 
         if head_commit is None:
@@ -434,6 +435,7 @@ def build_commit(
             self.systems,
             self.build_config.allow,
             self.build_config.pkgs,
+            self.build_config.options,
             check_meta=True,
         )
 
@@ -687,6 +689,7 @@ def start_review(
                 run=self.shell_options.run,
                 sandbox=self.shell_options.sandbox,
                 pkgs=self.build_config.pkgs,
+                options=self.build_config.options,
             )
             nix_shell(report.built_packages(), shell_config)
 
@@ -764,11 +767,12 @@ def parse_packages_xml(stdout: IO[str]) -> list[Package]:
     return packages
 
 
-def _list_packages_system(
+def _list_packages_system(  # noqa: PLR0913
     system: System,
     nix_path: str,
     allow: AllowedFeatures,
     pkgs: str | None = None,
+    options: tuple[tuple[str, str], ...] = (),
     *,
     check_meta: bool = False,
 ) -> list[Package]:
@@ -789,6 +793,7 @@ def _list_packages_system(
         "--allow-import-from-derivation"
         if allow.ifd
         else "--no-allow-import-from-derivation",
+        *[token for name, value in options for token in ("--option", name, value)],
         *(["-A", pkgs] if pkgs else []),
     ]
     if check_meta:
@@ -804,11 +809,12 @@ def _list_packages_system(
             return parse_packages_xml(f)
 
 
-def list_packages(
+def list_packages(  # noqa: PLR0913
     nix_path: str,
     systems: set[System],
     allow: AllowedFeatures,
     pkgs: str | None = None,
+    options: tuple[tuple[str, str], ...] = (),
     *,
     check_meta: bool = False,
 ) -> dict[System, list[Package]]:
@@ -820,6 +826,7 @@ def list_packages(
             allow=allow,
             check_meta=check_meta,
             pkgs=pkgs,
+            options=options,
         )
 
     return results
@@ -1018,6 +1025,7 @@ def build_config_from_args(
         num_eval_workers=args.num_eval_workers,
         max_memory_size=args.max_memory_size,
         pkgs=args.pkgs,
+        options=tuple((name, value) for name, value in args.option),
     )
 
 

tests/test_option_flag.py

@@ -0,0 +1,109 @@
+from __future__ import annotations
+
+import subprocess
+from pathlib import Path
+from typing import TYPE_CHECKING
+from unittest.mock import MagicMock, patch
+
+from nixpkgs_review.allow import AllowedFeatures
+from nixpkgs_review.cli import main, parse_args
+from nixpkgs_review.nix import BuildConfig, _nix_common_flags, _option_flags
+from nixpkgs_review.review import build_config_from_args
+
+if TYPE_CHECKING:
+    import pytest
+
+    from .conftest import Helpers
+
+
+def test_option_flags_expansion() -> None:
+    assert _option_flags((("cores", "4"), ("max-jobs", "2"))) == [
+        "--option",
+        "cores",
+        "4",
+        "--option",
+        "max-jobs",
+        "2",
+    ]
+
+
+def test_option_flags_empty() -> None:
+    assert _option_flags(()) == []
+
+
+def test_option_flags_preserves_order_on_repeated_name() -> None:
+    # Nix applies --option left-to-right, last occurrence wins; we must not
+    # dedupe or reorder, so the same last-wins behavior falls out naturally.
+    assert _option_flags((("cores", "4"), ("cores", "8"))) == [
+        "--option",
+        "cores",
+        "4",
+        "--option",
+        "cores",
+        "8",
+    ]
+
+
+def test_nix_common_flags_includes_extra_options() -> None:
+    flags = _nix_common_flags(AllowedFeatures([]), "", (("cores", "4"),))
+    assert flags[-3:] == ["--option", "cores", "4"]
+
+
+def test_nix_common_flags_no_options_by_default() -> None:
+    flags = _nix_common_flags(AllowedFeatures([]), "")
+    assert "cores" not in flags
+
+
+def test_parse_args_option_flag() -> None:
+    args = parse_args(
+        "nixpkgs-review",
+        ["rev", "HEAD", "--option", "cores", "4", "--option", "max-jobs", "2"],
+    )
+    assert args.option == [["cores", "4"], ["max-jobs", "2"]]
+
+
+def test_parse_args_option_flag_defaults_empty() -> None:
+    args = parse_args("nixpkgs-review", ["rev", "HEAD"])
+    assert args.option == []
+
+
+@patch("nixpkgs_review.review.current_system", return_value="x86_64-linux")
+def test_build_config_from_args_carries_options(
+    mock_current_system: MagicMock,
+) -> None:
+    args = parse_args(
+        "nixpkgs-review",
+        ["rev", "HEAD", "--option", "cores", "4", "--option", "max-jobs", "2"],
+    )
+    build_config: BuildConfig = build_config_from_args(
+        args, AllowedFeatures([]), nix_path="", nixpkgs_config=Path("/dev/null")
+    )
+    assert build_config.options == (("cores", "4"), ("max-jobs", "2"))
+    assert build_config.local_system == mock_current_system.return_value
+
+
+def test_option_flag_end_to_end(
+    helpers: Helpers, capsys: pytest.CaptureFixture[str]
+) -> None:
+    with helpers.nixpkgs() as nixpkgs:
+        nixpkgs.path.joinpath("pkg1.txt").write_text("foo")
+        subprocess.run(["git", "add", "."], check=True)
+        subprocess.run(["git", "commit", "-m", "example-change"], check=True)
+        path = main(
+            "nixpkgs-review",
+            [
+                "rev",
+                "HEAD",
+                "--remote",
+                str(nixpkgs.remote),
+                "--run",
+                "exit 0",
+                "--build-graph",
+                "nix",
+                "--option",
+                "cores",
+                "1",
+            ],
+        )
+        helpers.assert_built(path, "pkg1")
+        assert "--option cores 1" in capsys.readouterr().out