"Invalid marker" error when using hashes in requirements.txt

[Julian Edwards]

I have a requirements.txt file that has hashes in it defined as per the format that pip needs, e.g.

alembic==1.7.5 \
    --hash=sha256:7c328694a2e68f03ee971e63c3bd885846470373a5b532cf2c9f1601c413b153

When attempting to install my local package (developer mode, not sure that matters though), I get this kind of error:

  Traceback (most recent call last):
    File "/tmp/pip-build-env-ce9n1mxv/overlay/lib/python3.9/site-packages/pkg_resources/__init__.py", line 1369, in evaluate_marker
      marker = packaging.markers.Marker(text)
    File "/tmp/pip-build-env-ce9n1mxv/overlay/lib/python3.9/site-packages/pkg_resources/_vendor/packaging/markers.py", line 280, in __init__
      raise InvalidMarker(
  pkg_resources.extern.packaging.markers.InvalidMarker: Invalid marker: '(446438bdcca0e05bd45ea2de1668c1d9b032e1a9154c2c259092d77031ddd359 \\)', parse error at '446438bd'