pip-compile ignores deps with --pre in the input

[blueyed]

Using --pre in a requirements line results in the dependency to be ignored:

% echo '--pre channels' | pip-compile -q - -o -
#
# This file is autogenerated by pip-compile
# To update, run:
#
#    pip-compile --output-file=- -
#
--index-url http://localhost:3141/root/pypi/+simple/

(Noticed this when coming up with #817)
pip-compile, version 3.6.2.dev2+ga3ac5ca

[atugushev]

@blueyed

Do we really need --pre options in compiled requirements.txt? Since a package's pinned with a prerelease version it would be installed on pip-sync anyways.

BTW, I've noticed that --pre doesn't work in requirements.in at all. See #819.

[blueyed]

@atugushev
It is not needed, but I think it is a bug.
#819 is basically a duplicate of this one here.. :)

[blueyed]

But since #819 has more details, I'm closing this one here.