Fix requirements.txt parsing (#2683)

Resolves #2682

Author: gaborbernat

docs/changelog/2682.bugfix.rst

@@ -0,0 +1 @@
+Fix regression in ``requirements.txt`` parsing - by :user:`gaborbernat`.

src/tox/tox_env/python/pip/req_file.py

@@ -19,11 +19,11 @@ def __init__(self, raw: str, root: Path):
         self._req_parser_: RequirementsFile | None = None
 
     def _extend_parser(self, parser: ArgumentParser) -> None:
-        parser.add_argument("--no-deps", action="store_true", default=False)
+        parser.add_argument("--no-deps", action="store_true", dest="no_deps", default=False)
 
     def _merge_option_line(self, base_opt: Namespace, opt: Namespace, filename: str) -> None:
         super()._merge_option_line(base_opt, opt, filename)
-        if opt.no_deps:
+        if getattr(opt, "no_deps", False):  # if the option comes from a requirements file this flag is missing there
             base_opt.no_deps = True
 
     def _option_to_args(self, opt: Namespace) -> list[str]:

tests/tox_env/python/pip/test_req_file.py

@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+from argparse import Namespace
 from pathlib import Path
 
 import pytest
@@ -58,3 +59,11 @@ def test_req_with_no_deps(tmp_path: Path) -> None:
     python_deps = PythonDeps(raw="-rr.txt", root=tmp_path)
     with pytest.raises(ValueError, match="unrecognized arguments: --no-deps"):
         python_deps.requirements
+
+
+def test_opt_only_req_file(tmp_path: Path) -> None:
+    """deps with --hash should raise an exception."""
+    (tmp_path / "r.txt").write_text("--use-feature fast-deps")
+    python_deps = PythonDeps(raw="-rr.txt", root=tmp_path)
+    assert not python_deps.requirements
+    assert python_deps.options == Namespace(features_enabled=["fast-deps"])