Ignore pkg-resources in pip-sync

Fix #422

CHANGELOG.md

@@ -11,6 +11,7 @@ when `--allow-unsafe` was not set. ([#517](https://github.com/jazzband/pip-tools
 - Fixed bug where editable PyPI dependencies would have a `download_dir` and be exposed to `git-checkout-index`,
 (thus losing their VCS directory) and `python setup.py egg_info` fails. ([#385](https://github.com/jazzband/pip-tools/pull/385#) and [#538](https://github.com/jazzband/pip-tools/pull/538)). Thanks @blueyed and @dfee
 - Fixed bug where some primary dependencies were annotated with "via" info comments. ([#542](https://github.com/jazzband/pip-tools/pull/542)). Thanks @quantus
+- Fixed bug where pkg-resources would be removed by pip-sync in Ubuntu. ([#555](https://github.com/jazzband/pip-tools/pull/555)). Thanks @cemsbr
 
 # 1.9.0 (2017-04-12)
 

piptools/sync.py

@@ -11,6 +11,7 @@
     'pip',
     'pip-tools',
     'pip-review',
+    'pkg-resources',
     'setuptools',
     'wheel',
 ]

tests/test_sync.py

@@ -100,6 +100,16 @@ def test_diff_should_uninstall(fake_dist):
     assert to_uninstall == {'django'}  # no version spec when uninstalling
 
 
+def test_diff_should_not_uninstall(fake_dist):
+    ignored = ('pip==7.1.0', 'pip-tools==1.1.1', 'pip-review==1.1.1',
+               'pkg-resources==0.0.0', 'setuptools==34.0.0', 'wheel==0.29.0')
+    installed = [fake_dist(pkg) for pkg in ignored]
+    reqs = []
+
+    to_uninstall = diff(reqs, installed)[1]
+    assert to_uninstall == set()
+
+
 def test_diff_should_update(fake_dist, from_line):
     installed = [fake_dist('django==1.7')]
     reqs = [from_line('django==1.8')]