Switch out conditional requirement parser

[mvdbeek]

Fixes

Traceback (most recent call last):
  File "/storage/srv/galaxy/server/.venv/lib64/python3.9/site-packages/pkg_resources/_vendor/packaging/requirements.py", line 35, in __init__
    parsed = _parse_requirement(requirement_string)
  File "/storage/srv/galaxy/server/.venv/lib64/python3.9/site-packages/pkg_resources/_vendor/packaging/_parser.py", line 64, in parse_requirement
    return _parse_requirement(Tokenizer(source, rules=DEFAULT_RULES))
  File "/storage/srv/galaxy/server/.venv/lib64/python3.9/site-packages/pkg_resources/_vendor/packaging/_parser.py", line 73, in _parse_requirement
    name_token = tokenizer.expect(
  File "/storage/srv/galaxy/server/.venv/lib64/python3.9/site-packages/pkg_resources/_vendor/packaging/_tokenizer.py", line 140, in expect
    raise self.raise_syntax_error(f"Expected {expected}")
  File "/storage/srv/galaxy/server/.venv/lib64/python3.9/site-packages/pkg_resources/_vendor/packaging/_tokenizer.py", line 165, in raise_syntax_error
    raise ParserSyntaxError(
pkg_resources.extern.packaging._tokenizer.ParserSyntaxError: Expected package name at the start of dependency specifier
    "git+https://github.com/jakobmerljak/pyarcrest.git@dev"
    ^

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/storage/srv/galaxy/server/lib/galaxy/dependencies/__init__.py", line 312, in optional
    conditional = ConditionalDependencies(config_file)
  File "/storage/srv/galaxy/server/lib/galaxy/dependencies/__init__.py", line 45, in __init__
    self.get_conditional_requirements()
  File "/storage/srv/galaxy/server/lib/galaxy/dependencies/__init__.py", line 176, in get_conditional_requirements
    for req in pkg_resources.parse_requirements(open(crfile).readlines()):
  File "/storage/srv/galaxy/server/.venv/lib64/python3.9/site-packages/pkg_resources/__init__.py", line 3174, in __init__
    super(Requirement, self).__init__(requirement_string)
  File "/storage/srv/galaxy/server/.venv/lib64/python3.9/site-packages/pkg_resources/_vendor/packaging/requirements.py", line 37, in __init__
    raise InvalidRequirement(str(e)) from e
pkg_resources.extern.packaging.requirements.InvalidRequirement: Expected package name at the start of dependency specifier
    "git+https://github.com/jakobmerljak/pyarcrest.git@dev"
    ^

for advanced package specifiers that might be used during development.

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• I've included appropriate automated tests.
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[nsoranzo]

https://setuptools.pypa.io/en/latest/pkg_resources.html recommends packaging for requirements parsing, would https://packaging.pypa.io/en/stable/requirements.html work?
One less project dependency, which would otherwise need to be added to packages/app/setup.cfg as well.

[mvdbeek]

That's not exactly a replacement for parsing requirement files, we'd still have to handle comments and empty lines and other funky stuff that is allowed ... or live with the limitations. FWIW dparse is 900 lines in total and used by pyup.io