Only skip a file if `# flake8: noqa` is on a line by itself
A rather simple footgun enables someone who doesn't know the difference between
# noqa and
# flake8: noqa to accidentally turn off linting for a whole file:
import os # flake8: noqa import sys print(sys.version_info)
when they really just intended to remove the linting for a single line.
This PR changes the behaviour to only skip the entire file if the
# flake8: noqa comment is on a line by itself.