addoption "--run" behaviour is inconsistent.

[EvanTheB]

I created an option with parser.addoption("--run")
Using this option worked find with the command line
py.test --run argument
However using the alternative syntax
py.test --run=argument
Caused the failure py.test: error: argument --runxfail: ignored explicit argument 'abc'. I assume that the option matching is using prefixes. I think the behaviour of runxfail being triggered by --run is fine, however the behaviour should be consistent between the two ways of specifying command line options.

[RonnyPfannschmidt]

this seems to be a argparse bug known since 2013

[The-Compiler]

What's the argparse bug? Looks fine in a quick test to me:

>>> import argparse
>>> p = argparse.ArgumentParser()
>>> p.add_argument('--run', nargs=1)
>>> p.add_argument('--runxfail')
>>> p.parse_args(['--run=foo'])
Namespace(run=['foo'], runxfail=None)
>>> p.parse_args(['--run', 'foo'])
Namespace(run=['foo'], runxfail=None)

(also, I disagree this should be marked critical)

[RonnyPfannschmidt]

https://docs.python.org/2/library/argparse.html#partial-parsing

so in preparse we already kow runxfail but not run, thus runxfail is matched

[nicoddemus]

Closing this in favor of #1149