Evaluate PEP 508 environment markers for package dependencies

Previously any wheel dependencies that had an environment marker
(such as 'python_version>3.3') were simply ignored, leading to
missing packages in the Python environment constructed by bazel.

Fixes bazel-contrib#49

Author: nikhaldi

rules_python/whl.py

@@ -16,6 +16,7 @@
 import argparse
 import json
 import os
+import pkg_resources
 import re
 import zipfile
 
@@ -86,10 +87,10 @@ def dependencies(self, extra=None):
       if requirement.get('extra') != extra:
         # Match the requirements for the extra we're looking for.
         continue
-      if 'environment' in requirement:
-        # TODO(mattmoor): What's the best way to support "environment"?
-        # This typically communicates things like python version (look at
-        # "wheel" for a good example)
+      marker = requirement.get('environment')
+      if marker and not pkg_resources.evaluate_marker(marker):
+        # The current environment does not match the provided PEP 508 marker,
+        # so ignore this requirement.
         continue
       requires = requirement.get('requires', [])
       for entry in requires:

rules_python/whl_test.py

@@ -14,9 +14,12 @@
 
 import os
 import unittest
+import sys
 
 from rules_python import whl
 
+VERSION_TUPLE = sys.version_info.major, sys.version_info.minor
+
 
 def TestData(name):
   return os.path.join(os.environ['TEST_SRCDIR'], name)
@@ -60,11 +63,19 @@ def test_mock_whl(self):
     self.assertEqual(wheel.name(), 'mock')
     self.assertEqual(wheel.distribution(), 'mock')
     self.assertEqual(wheel.version(), '2.0.0')
+    if VERSION_TUPLE < (3, 3):
+      expected_deps = ['funcsigs', 'pbr', 'six']
+    else:
+      expected_deps = ['pbr', 'six']
     self.assertEqual(set(wheel.dependencies()),
-                     set(['pbr', 'six']))
+                     set(expected_deps))
     self.assertEqual('pypi__mock_2_0_0', wheel.repository_name())
     self.assertEqual(['docs', 'test'], wheel.extras())
-    self.assertEqual(set(wheel.dependencies(extra='docs')), set())
+    if VERSION_TUPLE  < (3, 0) or VERSION_TUPLE >= (3, 3):
+      expected_doc_deps = ['sphinx']
+    else:
+      expected_doc_deps = ['sphinx', 'Pygments', 'jinja2']
+    self.assertEqual(set(wheel.dependencies(extra='docs')), set(expected_doc_deps))
     self.assertEqual(set(wheel.dependencies(extra='test')), set(['unittest2']))
 
   def test_google_cloud_language_whl(self):
@@ -74,9 +85,12 @@ def test_google_cloud_language_whl(self):
     self.assertEqual(wheel.name(), 'google-cloud-language')
     self.assertEqual(wheel.distribution(), 'google_cloud_language')
     self.assertEqual(wheel.version(), '0.29.0')
+    expected_deps = ['google-gax', 'google-cloud-core',
+                     'googleapis-common-protos[grpc]']
+    if VERSION_TUPLE < (3, 4):
+      expected_deps.append('enum34')
     self.assertEqual(set(wheel.dependencies()),
-                     set(['google-gax', 'google-cloud-core',
-                          'googleapis-common-protos[grpc]']))
+                     set(expected_deps))
     self.assertEqual('pypi__google_cloud_language_0_29_0',
                      wheel.repository_name())
     self.assertEqual([], wheel.extras())