Ensure that a module within a namespace package can be found by --pyargs

[taschini]

This PR supersedes #1568 and addresses the problem highlighted in #1567 and in part #478.

See #1568 for the description of the test setup.

Unlike #1568, this PR does not attempt to emulate the import machinery to determine the filename of a package or directory, delegating instead most of the work to the pkgutil module of the standard library.

NB In case of a non-top-level module or package, pkgutil.find_loader will import the parent package or packages.

[coveralls]

Coverage increased (+0.04%) to 92.246% when pulling 2481b7a on taschini:pyargs-fix into 70fdab4 on pytest-dev:master.

[nicoddemus]

It is usually better to avoid bare except clauses like this... could this be replaced by except ImportError?

[taschini]

Appveyor caught a little problem with a test setup using PyPy on Windows: I'll fix that.

@nicoddemus I'll incorporate your feedback. The reason why that try-except clause is needed is that sometimes _parsearg() gets invoked with AssertionRewritingHook, which does not define a get_filename method, already in place. Hence, the exception you'll get is an AttributeError.

I'll catch explicitly that exception and add a comment to explain why that is necessary.

[coveralls]

Coverage increased (+0.005%) to 92.21% when pulling 5403f27 on taschini:pyargs-fix into 70fdab4 on pytest-dev:master.

[taschini]

I incorporated the feedback from @nicoddemus and also fixed a problem caused in a test on Windows by a file left open by PyPy and not immediately garbage collected.

[nicoddemus]

Thanks! 😁

LGTM. Could someone else take a look as well?

Also, we need a CHANGELOG entry and add @taschini to AUTHORS before merging.

[taschini]

Shall I add the entries in CHANGELOG and AUTHORS or is it something that typically you guys do?

[nicoddemus]

Please do. We usually ask for PR submitters to do it, but this has gone back and forth a few times already and I didn't want to ask for one more, hehehe. 😅

[nicoddemus]

It seems this is now in conflict. Would you please merge/rebase to fix it? Thanks!

[taschini]

Rebased the PR.

[coveralls]

Coverage decreased (-0.004%) to 92.21% when pulling 1218392 on taschini:pyargs-fix into 66e66f6 on pytest-dev:master.

[nicoddemus]

Thanks! 😁

I will merge this later unless someone says otherwise.

[nicoddemus]

Thanks, sorry for the delay! 😁