WIP: Add support for wheel build tags

At the moment, pip doesn't support ordering candidate installations
while considering build tags. This is meant to start adding that
support.

According to the PEP, the first contiguous set of integers in the build
tag should be sorted numerically. After that, they should be sorted
alphabetically.

Author: sigmavirus24

pip/index.py

@@ -266,6 +266,7 @@ def _candidate_sort_key(self, candidate):
               with the same version, would have to be considered equal
         """
         support_num = len(self.valid_tags)
+        build_tag = tuple()
         if candidate.location.is_wheel:
             # can raise InvalidWheelFilename
             wheel = Wheel(candidate.location.filename)
@@ -275,9 +276,13 @@ def _candidate_sort_key(self, candidate):
                     "can't be sorted." % wheel.filename
                 )
             pri = -(wheel.support_index_min(self.valid_tags))
+            if wheel.build_tag is not None:
+                match = re.match('^(\d+)(.*)$', wheel.build_tag)
+                build_tag_groups = match.groups()
+                build_tag = (int(build_tag_groups[0]), build_tag_groups[1])
         else:  # sdist
             pri = -(support_num)
-        return (candidate.version, pri)
+        return (candidate.version, build_tag, pri)
 
     def _validate_secure_origin(self, logger, location):
         # Determine if this url used a secure transport mechanism

pip/wheel.py

@@ -583,7 +583,7 @@ class Wheel(object):
 
     wheel_file_re = re.compile(
         r"""^(?P<namever>(?P<name>.+?)-(?P<ver>\d.*?))
-        ((-(?P<build>\d.*?))?-(?P<pyver>.+?)-(?P<abi>.+?)-(?P<plat>.+?)
+        ((-(?P<build>\d[^-]*?))?-(?P<pyver>.+?)-(?P<abi>.+?)-(?P<plat>.+?)
         \.whl|\.dist-info)$""",
         re.VERBOSE
     )
@@ -602,6 +602,7 @@ def __init__(self, filename):
         # we'll assume "_" means "-" due to wheel naming scheme
         # (https://github.com/pypa/pip/issues/1150)
         self.version = wheel_info.group('ver').replace('_', '-')
+        self.build_tag = wheel_info.group('build')
         self.pyversions = wheel_info.group('pyver').split('.')
         self.abis = wheel_info.group('abi').split('.')
         self.plats = wheel_info.group('plat').split('.')