Raise InvalidRequirement/Marker from exc

[Jackenmen]

This PR uses raise from exc syntax to improve the traceback from:

Traceback (most recent call last):
  File "/home/ubuntu/work/packaging/packaging/requirements.py", line 40, in __init__
    req = _RequirementTuple(*parse_named_requirement(requirement_string))
  File "/home/ubuntu/work/packaging/packaging/_parser.py", line 90, in parse_named_requirement
    error_message="Expected semicolon (followed by markers) or end of string",
  File "/home/ubuntu/work/packaging/packaging/_tokenizer.py", line 111, in expect
    raise self.raise_syntax_error(message=error_message)
  File "/home/ubuntu/work/packaging/packaging/_tokenizer.py", line 140, in raise_syntax_error
    self.position,
packaging._tokenizer.ParseExceptionError: Expected semicolon (followed by markers) or end of string
at position 59:
    tomli @ https://github.com/hukkin/tomli/archive/master.zip; python_version < '3.11'
                                                               ^

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/ubuntu/work/packaging/packaging/requirements.py", line 42, in __init__
    raise InvalidRequirement(str(e))
packaging.requirements.InvalidRequirement: Expected semicolon (followed by markers) or end of string
at position 59:
    tomli @ https://github.com/hukkin/tomli/archive/master.zip; python_version < '3.11'
                                                               ^

to:

Traceback (most recent call last):
  File "/home/ubuntu/work/packaging/packaging/requirements.py", line 40, in __init__
    req = _RequirementTuple(*parse_named_requirement(requirement_string))
  File "/home/ubuntu/work/packaging/packaging/_parser.py", line 90, in parse_named_requirement
    error_message="Expected semicolon (followed by markers) or end of string",
  File "/home/ubuntu/work/packaging/packaging/_tokenizer.py", line 111, in expect
    raise self.raise_syntax_error(message=error_message)
  File "/home/ubuntu/work/packaging/packaging/_tokenizer.py", line 140, in raise_syntax_error
    self.position,
packaging._tokenizer.ParseExceptionError: Expected semicolon (followed by markers) or end of string
at position 49:
    tomli@github.com/hukkin/tomli/archive/master.zip; python_version < '3.11'
                                                     ^

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

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/ubuntu/work/packaging/packaging/requirements.py", line 42, in __init__
    raise InvalidRequirement(str(e)) from e
packaging.requirements.InvalidRequirement: Expected semicolon (followed by markers) or end of string
at position 49:
    tomli@github.com/hukkin/tomli/archive/master.zip; python_version < '3.11'
                                                     ^

[brettcannon]

I think I would rather see the change be raise InvalidRequirement from e if there was a desire to suppress the duplicate output rather than toss out the parsing exception. At least for us having the full traceback helps debug issues.

[brettcannon]

Do you have an opinion, @pradyunsg ?

[pradyunsg]

I don’t have any opinion either way,

[Jackenmen]

I mostly made this PR because I found this traceback excessively big considering both exceptions convey the same amount of information. Still, I guess it would make more sense to use raise InvalidRequirement(...) from exc as InvalidRequirement is sort of a wrapper of the underlying exception and that's one of the cases this syntax is meant for. Just let me know what you want me to do and I'll update the PR if necessary.

[brettcannon]

Then please use the from exc form.

[brettcannon]

I'm not sure if repeating the string from e gets us anything. I think raising the appropriate exception is important for except clauses, but a person looking at the output can look at the traceback to see what ultimately triggered the exception.

Suggested change

	raise InvalidRequirement(str(e)) from e
	raise InvalidRequirement from e