packaging.tags.compatible_tags is not re-creating a new iterator

[jeroendecroos]

With the release of pip==20.0.1 a problem was observed as described here: pypa/pip#7626

The problem was tracked back to packaging.tags.compatible_tags

When no iterator is given for parameter platforms, an iterator is initialized:

packaging/packaging/tags.py

Line 332 in e664cdd

platforms = _platform_tags()

Which is then used in:

packaging/packaging/tags.py

Line 334 in e664cdd

for platform_ in platforms:

This should be the otherway around, to not reuse the exhausted iterator.

[brettcannon]

I'm not quite seeing the bug on our side. If no iterator is provided then we create one from _platform_tags() and then we use it in the for loop. The API specifically asks for an iterator, so I'm not seeing the issue. Are you suggesting we test for platforms is None?

[brettcannon]

nm, I see the issue now; it's the for loop using platforms being within another for loop.