Problem: requirements parse errors with new setuptools

Solution: use packaging APIs

src/zc/buildout/easy_install.py

@@ -18,12 +18,14 @@ It doesn't install scripts.  It uses setuptools and requires it to be
 installed.
 """
 
+import copy
 import distutils.errors
 import errno
 import glob
 import logging
 import os
 import pkg_resources
+from pkg_resources import packaging
 import py_compile
 import re
 import setuptools.archive_util
@@ -1618,30 +1620,25 @@ def redo_pyc(egg):
                 call_subprocess(args)
 
 def _constrained_requirement(constraint, requirement):
+    assert isinstance(requirement, pkg_resources.Requirement)
     if constraint[0] not in '<>':
         if constraint.startswith('='):
             assert constraint.startswith('==')
-            constraint = constraint[2:]
-        if constraint not in requirement:
+            version = constraint[2:]
+        else:
+            version = constraint
+            constraint = '==' + constraint
+        if version not in requirement:
             msg = ("The requirement (%r) is not allowed by your [versions] "
-                   "constraint (%s)" % (str(requirement), constraint))
+                   "constraint (%s)" % (str(requirement), version))
             raise IncompatibleConstraintError(msg)
-
-        # Sigh, copied from Requirement.__str__
-        extras = ','.join(requirement.extras)
-        if extras:
-            extras = '[%s]' % extras
-        return pkg_resources.Requirement.parse(
-            "%s%s==%s" % (requirement.project_name, extras, constraint))
-
-    if requirement.specs:
-        return pkg_resources.Requirement.parse(
-            str(requirement) + ',' + constraint
-            )
+        specifier = packaging.specifiers.SpecifierSet(constraint)
     else:
-        return pkg_resources.Requirement.parse(
-            str(requirement) + ' ' + constraint
-            )
+        specifier = requirement.specifier & constraint
+    constrained = copy.deepcopy(requirement)
+    constrained.specifier = specifier
+    return pkg_resources.Requirement.parse(str(constrained))
+
 
 class IncompatibleConstraintError(zc.buildout.UserError):
     """A specified version is incompatible with a given requirement.

src/zc/buildout/tests/test_extras.py

+# -*- coding: utf-8 -*-
+##############################################################################
+#
+# Copyright (c) 2020 Zope Foundation and Contributors.
+# All Rights Reserved.
+#
+# This software is subject to the provisions of the Zope Public License,
+# Version 2.1 (ZPL).  A copy of the ZPL should accompany this distribution.
+# THIS SOFTWARE IS PROVIDED "AS IS" AND ANY AND ALL EXPRESS OR IMPLIED
+# WARRANTIES ARE DISCLAIMED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+# WARRANTIES OF TITLE, MERCHANTABILITY, AGAINST INFRINGEMENT, AND FITNESS
+# FOR A PARTICULAR PURPOSE.
+#
+##############################################################################
+import doctest
+import re
+from zope.testing import renormalizing
+import zc.buildout.testing
+from zc.buildout.tests import easy_install_SetUp
+from zc.buildout.tests import normalize_bang
+
+
+def install_extras_with_greater_than_constrains():
+    """
+    There was a bug that caused extras in requirements to be lost.
+
+    >>> working = tmpdir('working')
+    >>> cd(working)
+    >>> mkdir('dependency')
+    >>> cd('dependency')
+    >>> with open('setup.py', 'w') as f:
+    ...    _ = f.write('''
+    ... from setuptools import setup
+    ... setup(name='dependency', version='1.0',
+    ...       url='x', author='x', author_email='x',
+    ...       py_modules=['t'])
+    ... ''')
+    >>> open('README', 'w').close()
+    >>> open('t.py', 'w').close()
+
+    >>> sdist('.', sample_eggs)
+    >>> cd(working)
+    >>> mkdir('extras')
+    >>> cd('extras')
+    >>> with open('setup.py', 'w') as f:
+    ...    _ = f.write('''
+    ... from setuptools import setup
+    ... setup(name='extraversiondemo', version='1.0',
+    ...       url='x', author='x', author_email='x',
+    ...       extras_require=dict(foo=['dependency']), py_modules=['t'])
+    ... ''')
+    >>> open('README', 'w').close()
+    >>> open('t.py', 'w').close()
+
+    >>> sdist('.', sample_eggs)
+    >>> mkdir('dest')
+    >>> ws = zc.buildout.easy_install.install(
+    ...     ['extraversiondemo[foo]'], 'dest', links=[sample_eggs],
+    ...     versions = dict(extraversiondemo='1.0', dependency='>0.9')
+    ... )
+    >>> sorted(dist.key for dist in ws)
+    ['dependency', 'extraversiondemo']
+    """
+
+
+def test_suite():
+    return doctest.DocTestSuite(
+        setUp=easy_install_SetUp,
+        tearDown=zc.buildout.testing.buildoutTearDown,
+        checker=renormalizing.RENormalizing([
+            zc.buildout.testing.normalize_path,
+            zc.buildout.testing.normalize_endings,
+            zc.buildout.testing.normalize_script,
+            zc.buildout.testing.normalize_egg_py,
+            zc.buildout.testing.normalize___pycache__,
+            zc.buildout.testing.not_found,
+            zc.buildout.testing.normalize_exception_type_for_python_2_and_3,
+            zc.buildout.testing.adding_find_link,
+            zc.buildout.testing.python27_warning,
+            zc.buildout.testing.python27_warning_2,
+            normalize_bang,
+            (re.compile(r'^(\w+\.)*(Missing\w+: )'), '\2'),
+            (re.compile(r"buildout: Running \S*setup.py"),
+             'buildout: Running setup.py'),
+            (re.compile(r'pip-\S+-'),
+             'pip.egg'),
+            (re.compile(r'setuptools-\S+-'),
+             'setuptools.egg'),
+            (re.compile(r'zc.buildout-\S+-'),
+             'zc.buildout.egg'),
+            (re.compile(r'pip = \S+'), 'pip = 20.0.0'),
+            (re.compile(r'setuptools = \S+'), 'setuptools = 0.7.99'),
+            (re.compile(r'File "\S+one.py"'),
+             'File "one.py"'),
+            (re.compile(r'We have a develop egg: (\S+) (\S+)'),
+             r'We have a develop egg: \1 V'),
+            (re.compile(r'Picked: setuptools = \S+'),
+             'Picked: setuptools = V'),
+            (re.compile('[-d]  pip'), '-  pip'),
+            (re.compile('[-d]  setuptools'), '-  setuptools'),
+            (re.compile(r'\\[\\]?'), '/'),
+            (re.compile(
+                '-q develop -mxN -d "/sample-buildout/develop-eggs'),
+             '-q develop -mxN -d /sample-buildout/develop-eggs'
+             ),
+            (re.compile(r'^[*]...'), '...'),
+            # for
+            # bug_92891
+            # bootstrap_crashes_with_egg_recipe_in_buildout_section
+            (re.compile(r"Unused options for buildout: 'eggs' 'scripts'\."),
+             "Unused options for buildout: 'scripts' 'eggs'."),
+            # Python 3.4 changed the wording of NameErrors
+            (re.compile('NameError: global name'), 'NameError: name'),
+            # fix for test_distutils_scripts_using_import_are_properly_parsed
+            # and test_distutils_scripts_using_from_are_properly_parsed
+            # win32 apparently adds a " around sys.executable
+            (re.compile('#!"python"'), '#!python'),
+            ]),
+        )