feat: support PEP 723 directly

Signed-off-by: Henry Schreiner <henryschreineriii@gmail.com>

fix: version based on pipx

Signed-off-by: Henry Schreiner <henryschreineriii@gmail.com>

fix: subprocess on Windows

Signed-off-by: Henry Schreiner <henryschreineriii@gmail.com>

fix: uv or virtualenv, test

Signed-off-by: Henry Schreiner <henryschreineriii@gmail.com>

fix: windows

Signed-off-by: Henry Schreiner <henryschreineriii@gmail.com>

fix: ignore errors in rmtree (3.8+ should be fine on Windows now)

fix: resolve nox path on Windows

Signed-off-by: Henry Schreiner <henryschreineriii@gmail.com>

docs/tutorial.rst

@@ -597,8 +597,8 @@ the tags, so all three sessions:
     * flake8
 
 
-Running without the nox command
--------------------------------
+Running without the nox command or adding dependencies
+------------------------------------------------------
 
 With a few small additions to your noxfile, you can support running using only
 a generalized Python runner, such as ``pipx run noxfile.py``, ``uv run
@@ -618,6 +618,13 @@ And the following block of code:
    if __name__ == "__main__":
        nox.main()
 
+If this comment block is present, nox will also read it, and run a custom
+environment (``_nox_script_mode``) if the dependencies are not met in the
+current environment. This allows you to specify dependencies for your noxfile
+or a minimum version of nox here (``requires-python`` version setting not
+supported yet, but planned). You can control this with
+``--script-mode``/``NOX_SCRIPT_MODE``; ``none`` will deactivate it, and
+``fresh`` will rebuild it; the default is ``reuse``.
 
 Next steps
 ----------

nox/_cli.py

@@ -16,12 +16,24 @@
 
 from __future__ import annotations
 
+import importlib.metadata
+import os
+import shutil
+import subprocess
 import sys
-from typing import Any
+from collections.abc import Generator
+from pathlib import Path
+from typing import Any, NoReturn
 
+import packaging.requirements
+import packaging.utils
+
+import nox.command
+import nox.virtualenv
 from nox import _options, tasks, workflow
 from nox._version import get_nox_version
 from nox.logger import setup_logging
+from nox.project import load_toml
 
 
 def execute_workflow(args: Any) -> int:
@@ -45,6 +57,82 @@ def execute_workflow(args: Any) -> int:
     )
 
 
+def get_dependencies(
+    req: packaging.requirements.Requirement,
+) -> Generator[packaging.requirements.Requirement, None, None]:
+    """
+    Gets all dependencies. Raises ModuleNotFoundError if a package is not installed.
+    """
+    info = importlib.metadata.metadata(req.name)
+    yield req
+
+    dist_list = info.get_all("requires-dist") or []
+    extra_list = [packaging.requirements.Requirement(mk) for mk in dist_list]
+    for extra in req.extras:
+        for ireq in extra_list:
+            if ireq.marker and not ireq.marker.evaluate({"extra": extra}):
+                continue
+            yield from get_dependencies(ireq)
+
+
+def check_dependencies(dependencies: list[str]) -> bool:
+    """
+    Checks to see if a list of dependencies is currently installed.
+    """
+    itr_deps = (packaging.requirements.Requirement(d) for d in dependencies)
+    deps = [d for d in itr_deps if not d.marker or d.marker.evaluate()]
+
+    # Select the one nox dependency (required)
+    nox_dep = [d for d in deps if packaging.utils.canonicalize_name(d.name) == "nox"]
+    if not nox_dep:
+        msg = "Must have a nox dependency in TOML script dependencies"
+        raise ValueError(msg)
+
+    try:
+        expanded_deps = {d for req in deps for d in get_dependencies(req)}
+    except ModuleNotFoundError:
+        return False
+
+    for dep in expanded_deps:
+        if dep.specifier:
+            version = importlib.metadata.version(dep.name)
+            if not dep.specifier.contains(version):
+                return False
+
+    return True
+
+
+def run_script_mode(envdir: Path, reuse: bool, dependencies: list[str]) -> NoReturn:
+    envdir.mkdir(exist_ok=True)
+    noxenv = envdir.joinpath("_nox_script_mode")
+    venv = nox.virtualenv.get_virtualenv(
+        "uv",
+        "virtualenv",
+        reuse_existing=reuse,
+        envdir=str(noxenv),
+    )
+    venv.create()
+    venv.env["NOX_SCRIPT_MODE"] = "none"
+    cmd = ["uv", "pip", "install"] if venv.venv_backend == "uv" else ["pip", "install"]
+    subprocess.run([*cmd, *dependencies], env=venv.env, check=True)
+    nox_cmd = shutil.which("nox", path=venv.env["PATH"])
+    assert nox_cmd is not None, "Nox must be discoverable when installed"
+    # The os.exec functions don't work properly on Windows
+    if sys.platform.startswith("win"):
+        raise SystemExit(
+            subprocess.run(
+                [nox_cmd, *sys.argv[1:]],
+                env=venv.env,
+                stdout=None,
+                stderr=None,
+                encoding="utf-8",
+                text=True,
+                check=False,
+            ).returncode
+        )
+    os.execle(nox_cmd, nox_cmd, *sys.argv[1:], venv.env)  # pragma: nocover
+
+
 def main() -> None:
     args = _options.options.parse_args()
 
@@ -59,6 +147,19 @@ def main() -> None:
     setup_logging(
         color=args.color, verbose=args.verbose, add_timestamp=args.add_timestamp
     )
+    nox_script_mode = os.environ.get("NOX_SCRIPT_MODE", "") or args.script_mode
+    if nox_script_mode not in {"none", "reuse", "fresh"}:
+        msg = f"Invalid NOX_SCRIPT_MODE: {nox_script_mode!r}, must be one of 'none', 'reuse', or 'fresh'"
+        raise SystemExit(msg)
+    if nox_script_mode != "none":
+        toml_config = load_toml(os.path.expandvars(args.noxfile), missing_ok=True)
+        dependencies = toml_config.get("dependencies")
+        if dependencies is not None:
+            valid_env = check_dependencies(dependencies)
+            # Coverage misses this, but it's covered via subprocess call
+            if not valid_env:  # pragma: nocover
+                envdir = Path(args.envdir or ".nox")
+                run_script_mode(envdir, nox_script_mode == "reuse", dependencies)
 
     exit_code = execute_workflow(args)
 

nox/_options.py

@@ -321,6 +321,13 @@ def _tag_completer(
         action="store_true",
         help="Show the Nox version and exit.",
     ),
+    _option_set.Option(
+        "script_mode",
+        "--script-mode",
+        group=options.groups["general"],
+        choices=["none", "fresh", "reuse"],
+        default="reuse",
+    ),
     _option_set.Option(
         "list_sessions",
         "-l",

nox/project.py

@@ -34,14 +34,19 @@ def __dir__() -> list[str]:
 )
 
 
-def load_toml(filename: os.PathLike[str] | str) -> dict[str, Any]:
+def load_toml(
+    filename: os.PathLike[str] | str, *, missing_ok: bool = False
+) -> dict[str, Any]:
     """
     Load a toml file or a script with a PEP 723 script block.
 
     The file must have a ``.toml`` extension to be considered a toml file or a
     ``.py`` extension / no extension to be considered a script. Other file
     extensions are not valid in this function.
 
+    If ``missing_ok``, this will return an empty dict if a script block was not
+    found, otherwise it will raise a error.
+
     Example:
 
     .. code-block:: python
@@ -55,7 +60,7 @@ def myscript(session):
     if filepath.suffix == ".toml":
         return _load_toml_file(filepath)
     if filepath.suffix in {".py", ""}:
-        return _load_script_block(filepath)
+        return _load_script_block(filepath, missing_ok=missing_ok)
     msg = f"Extension must be .py or .toml, got {filepath.suffix}"
     raise ValueError(msg)
 
@@ -65,12 +70,14 @@ def _load_toml_file(filepath: Path) -> dict[str, Any]:
         return tomllib.load(f)
 
 
-def _load_script_block(filepath: Path) -> dict[str, Any]:
+def _load_script_block(filepath: Path, *, missing_ok: bool) -> dict[str, Any]:
     name = "script"
     script = filepath.read_text(encoding="utf-8")
     matches = list(filter(lambda m: m.group("type") == name, REGEX.finditer(script)))
 
     if not matches:
+        if missing_ok:
+            return {}
         raise ValueError(f"No {name} block found in {filepath}")
     if len(matches) > 1:
         raise ValueError(f"Multiple {name} blocks found in {filepath}")

nox/virtualenv.py

@@ -306,7 +306,7 @@ def _clean_location(self) -> bool:
             if self.reuse_existing and is_conda:
                 return False
             if not is_conda:
-                shutil.rmtree(self.location)
+                shutil.rmtree(self.location, ignore_errors=True)
             else:
                 cmd = [
                     self.conda_cmd,
@@ -318,8 +318,7 @@ def _clean_location(self) -> bool:
                 ]
                 nox.command.run(cmd, silent=True, log=False)
             # Make sure that location is clean
-            with contextlib.suppress(FileNotFoundError):
-                shutil.rmtree(self.location)
+            shutil.rmtree(self.location, ignore_errors=True)
 
         return True
 
@@ -446,7 +445,7 @@ def _clean_location(self) -> bool:
                 and self._check_reused_environment_interpreter()
             ):
                 return False
-            shutil.rmtree(self.location)
+            shutil.rmtree(self.location, ignore_errors=True)
         return True
 
     def _read_pyvenv_cfg(self) -> dict[str, str] | None:

tests/resources/noxfile_script_mode.py

@@ -0,0 +1,12 @@
+# /// script
+# dependencies = ["nox", "cowsay"]
+# ///
+
+import cowsay
+
+import nox
+
+
+@nox.session
+def example(session: nox.Session) -> None:
+    print(cowsay.cow("hello_world"))

tests/test__cli.py

@@ -0,0 +1,68 @@
+import importlib.metadata
+import importlib.util
+import sys
+
+import packaging.requirements
+import packaging.version
+import pytest
+
+import nox._cli
+
+
+def test_get_dependencies():
+    if importlib.util.find_spec("tox") is None:
+        with pytest.raises(ModuleNotFoundError):
+            list(
+                nox._cli.get_dependencies(
+                    packaging.requirements.Requirement("nox[tox_to_nox]")
+                )
+            )
+    else:
+        deps = nox._cli.get_dependencies(
+            packaging.requirements.Requirement("nox[tox_to_nox]")
+        )
+        dep_list = {
+            "nox",
+            "argcomplete",
+            "colorlog",
+            "dependency-groups",
+            "packaging",
+            "virtualenv",
+            "jinja2",
+            "tox",
+        }
+        if sys.version_info < (3, 11):
+            dep_list.add("tomli")
+        assert {d.name for d in deps} == dep_list
+
+
+def test_version_check():
+    current_version = packaging.version.Version(importlib.metadata.version("nox"))
+
+    assert nox._cli.check_dependencies([f"nox>={current_version}"])
+    assert not nox._cli.check_dependencies([f"nox>{current_version}"])
+
+    plus_one = packaging.version.Version(
+        f"{current_version.major}.{current_version.minor}.{current_version.micro+1}"
+    )
+    assert not nox._cli.check_dependencies([f"nox>={plus_one}"])
+
+
+def test_nox_check():
+    with pytest.raises(ValueError, match="Must have a nox"):
+        nox._cli.check_dependencies(["packaging"])
+
+    with pytest.raises(ValueError, match="Must have a nox"):
+        nox._cli.check_dependencies([])
+
+
+def test_unmatched_specifier():
+    assert not nox._cli.check_dependencies(["packaging<1", "nox"])
+
+
+def test_invalid_mode(monkeypatch: pytest.MonkeyPatch):
+    monkeypatch.setenv("NOX_SCRIPT_MODE", "invalid")
+    monkeypatch.setattr(sys, "argv", ["nox"])
+
+    with pytest.raises(SystemExit, match="Invalid NOX_SCRIPT_MODE"):
+        nox._cli.main()

tests/test_main.py

@@ -951,3 +951,46 @@ def test_symlink_sym_not(monkeypatch):
     monkeypatch.chdir(Path(RESOURCES) / "sym_dir")
     res = subprocess.run([sys.executable, "-m", "nox", "-s", "orig"], check=False)
     assert res.returncode == 1
+
+
+def test_noxfile_script_mode():
+    job = subprocess.run(
+        [
+            sys.executable,
+            "-m",
+            "nox",
+            "-f",
+            Path(RESOURCES) / "noxfile_script_mode.py",
+            "-s",
+            "example",
+        ],
+        check=False,
+        capture_output=True,
+        text=True,
+    )
+    print(job.stdout)
+    print(job.stderr)
+    assert job.returncode == 0
+    assert "hello_world" in job.stdout
+
+
+def test_noxfile_no_script_mode():
+    env = os.environ.copy()
+    env["NOX_SCRIPT_MODE"] = "none"
+    job = subprocess.run(
+        [
+            sys.executable,
+            "-m",
+            "nox",
+            "-f",
+            Path(RESOURCES) / "noxfile_script_mode.py",
+            "-s",
+            "example",
+        ],
+        env=env,
+        check=False,
+        capture_output=True,
+        text=True,
+    )
+    assert job.returncode == 1
+    assert "No module named 'cowsay'" in job.stderr