setuptools.dist imports packaging, but check_specifier accesses packaging.specifiers

[jimfulton]

This causes an attribute error in check_specifier.

[jimfulton]

FWIW, this is breaking a deployment I'm dealing with.

(I'm working around it.)

[jaraco]

This issue probably emerged in Setuptools 34 when the vendoring was removed (ff371f1), as dist no longer imports pkg_resources to get the externs (which would import these submodules).

[jimfulton]

The bug became effective then. :)

[jaraco]

I believe this report is a duplicate of #967.

[jimfulton]

Yup