fix: error with helpful message if invalid option is set via nox.options

[henryiii]

Fix part of #869 - make sure only valid options are set.

The most recent commit also adds static typing for nox.options.

[henryiii]

I was testing out attrs in order to get validation, and found one type that was wrong - verbose was getting set to None. Since it's never checked for None specifically, I fixed the default.

Here's the patch to move to attrs:

diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
index 1f4d45f..2fab09e 100644
--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -37,6 +37,7 @@ repos:
         files: ^nox/
         args: []
         additional_dependencies:
+          - attrs
           - jinja2
           - packaging
           - importlib_metadata
diff --git a/nox/_option_set.py b/nox/_option_set.py
index d0a0297..e99413e 100644
--- a/nox/_option_set.py
+++ b/nox/_option_set.py
@@ -20,7 +20,6 @@ from __future__ import annotations

 import argparse
 import collections
-import dataclasses
 import functools
 from argparse import ArgumentError as ArgumentError  # noqa: PLC0414
 from argparse import ArgumentParser, Namespace
@@ -28,41 +27,30 @@ from collections.abc import Callable, Iterable
 from typing import Any, Literal

 import argcomplete
+import attrs
+import attrs.validators as av

+av_opt_str = av.optional(av.instance_of(str))
+av_opt_list_str = av.optional(av.deep_iterable(member_validator=av.instance_of(str), iterable_validator=attrs.validators.instance_of(list)))
+av_bool = av.instance_of(bool)

-# Python 3.10+ has slots=True (or attrs does), also kwonly=True
-@dataclasses.dataclass
+
+@attrs.define(slots=True, kw_only=True)
 class NoxOptions:
-    __slots__ = (
-        "default_venv_backend",
-        "envdir",
-        "error_on_external_run",
-        "error_on_missing_interpreters",
-        "force_venv_backend",
-        "keywords",
-        "pythons",
-        "report",
-        "reuse_existing_virtualenvs",
-        "reuse_venv",
-        "sessions",
-        "stop_on_first_error",
-        "tags",
-        "verbose",
-    )
-    default_venv_backend: None | str
-    envdir: None | str
-    error_on_external_run: bool
-    error_on_missing_interpreters: bool
-    force_venv_backend: None | str
-    keywords: None | list[str]
-    pythons: None | list[str]
-    report: None | str
-    reuse_existing_virtualenvs: bool
-    reuse_venv: None | Literal["no", "yes", "never", "always"]
-    sessions: None | list[str]
-    stop_on_first_error: bool
-    tags: None | list[str]
-    verbose: bool
+    default_venv_backend: None | str = attrs.field(validator=av_opt_str)
+    envdir: None | str = attrs.field(validator=av_opt_str)
+    error_on_external_run: bool = attrs.field(validator=av_bool)
+    error_on_missing_interpreters: bool = attrs.field(validator=av_bool)
+    force_venv_backend: None | str = attrs.field(validator=av_opt_str)
+    keywords: None | list[str] = attrs.field(validator=av_opt_list_str)
+    pythons: None | list[str] = attrs.field(validator=av_opt_list_str)
+    report: None | str = attrs.field(validator=av_opt_str)
+    reuse_existing_virtualenvs: bool = attrs.field(validator=av_bool)
+    reuse_venv: None | Literal["no", "yes", "never", "always"] = attrs.field(validator=av.optional(av.in_(["no", "yes", "never", "always"])))
+    sessions: None | list[str] = attrs.field(validator=av_opt_list_str)
+    stop_on_first_error: bool = attrs.field(validator=av_bool)
+    tags: None | list[str] = attrs.field(validator=av_opt_list_str)
+    verbose: bool = attrs.field(validator=av_bool)


 class OptionGroup:
diff --git a/pyproject.toml b/pyproject.toml
index 3781be7..df38d44 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -41,6 +41,7 @@ classifiers = [
 ]
 dependencies = [
   "argcomplete<4,>=1.9.4",
+  "attrs>=23.1",
   "colorlog<7,>=2.6.1",
   "packaging>=20.9",
   "tomli>=1; python_version<'3.11'",

Might be an interesting followup. Attrs is a highly respected, zero dependency, small library and used by things like pytest.