pip-compile with generate hashes is very slow for new requirements.txt generation

[graingert]

Could probably do with a progress bar

Environment Versions

1. OS Type Ubuntu
2. Python version: $ python -V 3.6
3. pip version: $ pip --version n/a
4. pip-tools version: $ pip-compile --version master

Steps to replicate

use geenrate-hashes with a fairly big package graph

Expected result

generated hashes turn up in requirements.txt and pip-compile does not appear to hang

Actual result

generated hashes turn up in requirements.txt but pip-compile appears to hang

[graingert]

#521 was closed by #641 but it doesn't actually help my use-case, where I regularly regenerate my requirements.txt

[vphilippon]

Allright, agreed. We'll track this one for the case of the first generation.

[devxpy]

Can we please have some sort of progress bar? Quite frustrating to just see it sit there..

[atugushev]

Progressbar added in #743. Use --verbose mode.