pip source fails to track requirements with setuptools_scm

Summary

pip source ignores setuptools_scm because it breaks convention and uses underscores instead of dashes in filenames. pip source should use looser regular expression or better yet move to pip freeze

Steps to reproduce

Have an element with local source requirements.txt which contains requests and setuptools_scm (or setuptools-scm, doesn't matter).

What is the current bug behavior?

pip will download setuptools-scm as setuptools_scm.version.extension so pip source will not see it and omits it in track.

What is the expected correct behavior?

pip source can track setuptools_scm

Relevant logs and/or screenshots

Possible fixes

Other relevant information

• BuildStream version affected: 1.4.1, master.

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