Support markers in requirements

It's now possible to specify requirements markers in requirements.
Examples::

    futures; python_version < '2.7'
    mock; python_version < '3.3'
    nose
    ordereddict; python_version < '2.7'
    unittest2; python_version < '2.7'

The separator is "; ". For convinience, ";" alone is also supported, but
no in URLs. The ";" character is a legit and common character in an URL.
Example of valid URL without markers::

    http://foo.com/?p=bar.git;a=snapshot;h=v0.1;sf=tgz

Example of URL with markers::

    http://foo.com/?p=bar.git;a=snapshot;h=v0.1;sf=tgz; python_version < '3.3'

docs/reference/pip_install.rst

@@ -29,6 +29,12 @@ and like arguments to :ref:`pip install`, the following forms are supported::
     [-e] <local project path>
     [-e] <vcs project url>
 
+Since version 6.0, pip also supports markers using the "; " separator.
+Examples::
+
+    futures; python_version < '2.7'
+    http://my.package.repo/SomePackage-1.0.4.zip; python_version >= '3.4'
+
 See the :ref:`pip install Examples<pip install Examples>` for examples of all these forms.
 
 A line that begins with ``#`` is treated as a comment and ignored. Whitespace

pip/req/req_install.py

@@ -13,6 +13,7 @@ from distutils import sysconfig
 from email.parser import FeedParser
 
 from pip._vendor import pkg_resources, six
+from pip._vendor.distlib.markers import interpret as markers_interpret
 from pip._vendor.six.moves import configparser
 from pip._vendor.six.moves.urllib import parse as urllib_parse
 
@@ -116,8 +117,12 @@ class InstallRequirement(object):
         requirement, directory containing 'setup.py', filename, or URL.
         """
         url = None
-        if ';' in name:
-            name, markers = name.split(';', 1)
+        if is_url(name):
+            marker_sep = '; '
+        else:
+            marker_sep = ';'
+        if marker_sep in name:
+            name, markers = name.split(marker_sep, 1)
             markers = markers.strip()
             if not markers:
                 markers = None
@@ -737,7 +742,7 @@ exec(compile(
 
     def match_markers(self):
         if self.markers is not None:
-            return markers.interpret(self.markers)
+            return markers_interpret(self.markers)
         else:
             return True
 

tests/unit/test_req.py

@@ -1,5 +1,6 @@
 import os
 import shutil
+import sys
 import tempfile
 
 import pytest
@@ -104,6 +105,63 @@ class TestInstallRequirement(object):
         req = InstallRequirement.from_editable(url)
         assert req.url == url
 
+    def test_markers(self):
+        for line in (
+            # recommanded syntax
+            'mock3; python_version >= "3"',
+            # with more spaces
+            'mock3 ; python_version >= "3" ',
+            # without spaces
+            'mock3;python_version >= "3"',
+        ):
+            req = InstallRequirement.from_line(line)
+            assert req.req.project_name == 'mock3'
+            assert req.req.specs == []
+            assert req.markers == 'python_version >= "3"'
+
+    def test_markers_semicolon(self):
+        # check that the markers can contain a semicolon
+        req = InstallRequirement.from_line('semicolon; os_name == "a; b"')
+        assert req.req.project_name == 'semicolon'
+        assert req.req.specs == []
+        assert req.markers == 'os_name == "a; b"'
+
+    def test_markers_url(self):
+        # test "URL; markers" syntax
+        url = 'http://foo.com/?p=bar.git;a=snapshot;h=v0.1;sf=tgz'
+        line = '%s; python_version >= "3"' % url
+        req = InstallRequirement.from_line(line)
+        assert req.url == url, req.url
+        assert req.markers == 'python_version >= "3"'
+
+        # without space, markers are part of the URL
+        url = 'http://foo.com/?p=bar.git;a=snapshot;h=v0.1;sf=tgz'
+        line = '%s;python_version >= "3"' % url
+        req = InstallRequirement.from_line(line)
+        assert req.url == line, req.url
+        assert req.markers is None
+
+    def test_markers_match(self):
+        # match
+        for markers in (
+            'python_version >= "1.0"',
+            'sys_platform == %r' % sys.platform,
+        ):
+            line = 'name; ' + markers
+            req = InstallRequirement.from_line(line)
+            assert req.markers == markers
+            assert req.match_markers()
+
+        # don't match
+        for markers in (
+            'python_version >= "5.0"',
+            'sys_platform != %r' % sys.platform,
+        ):
+            line = 'name; ' + markers
+            req = InstallRequirement.from_line(line)
+            assert req.markers == markers
+            assert not req.match_markers()
+
 
 def test_requirements_data_structure_keeps_order():
     requirements = Requirements()