confused by symlinks pointing to virtualenv gives FIRSTPARTY not THIRDPARTY

[brianmay]

On my box using isort 4.3.10

lrwxrwxrwx 1 brian brian 36 Aug  8  2018 /home/brian/.virtualenvs -> /home/brian/.local/share/virtualenvs

This appears to get isort confused, and it can incorrectly categorize third party imports as first party.

from-type place_module for django_cron returned FIRSTPARTY

If I redo with another virtual environment that doesn't have symlinks it shows:

from-type place_module for django_cron returned THIRDPARTY

Which I believe is correct.

I believe it is failing here: https://github.com/timothycrosley/isort/blob/f6ff653fbf149b67cef1e553940b788a9afa685e/isort/finders.py#L176

Where self.virtual_env_src contains /home/brian/.virtualenvs/energy_rating/src/ and prefix contains /home/brian/.local/share/virtualenvs/energy_rating/src/django-cron

I suspect the solution might be to apply os.path.realpath() on self.virtual_env_src, which would turn it into /home/brian/.local/share/virtualenvs/energy_rating/src and the condition will pass.

[brianmay]

For the record, same problem with latest version from develop branch.

[brianmay]

This should be fixed in #877.