make install of unpinned setuptools much quicker

by patching `pkg_resources.Distribution`.

CHANGES.rst

@@ -4,7 +4,8 @@ Change History
 2.13.4 (unreleased)
 ===================
 
-- Nothing changed yet.
+- Patch ``pkg_resources.Distribution`` to make install of unpinned versions quicker.
+  Most obvious with ``setuptools``.
 
 
 2.13.3 (2020-02-11)

src/zc/buildout/__init__.py

@@ -13,6 +13,8 @@
 ##############################################################################
 """Buildout package
 """
+import zc.buildout.patches # NOQA
+
 
 class UserError(Exception):
     """Errors made by a user

src/zc/buildout/patches.py

+##############################################################################
+#
+# Copyright (c) 2006 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.
+#
+##############################################################################
+
+
+def patch_Distribution():
+    try:
+        from pkg_resources import _remove_md5_fragment
+        from pkg_resources import Distribution
+
+        if hasattr(Distribution, 'location'):
+            return
+
+        # prepare any Distribution built before monkeypatch
+        from pkg_resources import working_set
+        for dist in working_set:
+            dist._location = dist.location
+            dist._location_without_md5 = _remove_md5_fragment(dist.location)
+
+        def hashcmp(self):
+            without_md5 = getattr(self, '_location_without_md5', '')
+            return (
+                self.parsed_version,
+                self.precedence,
+                self.key,
+                without_md5,
+                self.py_version or '',
+                self.platform or '',
+            )
+
+        def get_location(self):
+            try:
+                result = self._location
+            except AttributeError:
+                result = ''
+            return result
+
+        def set_location(self, l):
+            self._location = l
+            self._location_without_md5 = _remove_md5_fragment(l)
+
+        setattr(Distribution, 'location', property(get_location, set_location))
+        setattr(Distribution, 'hashcmp', property(hashcmp))
+    except ImportError:
+        return
+
+
+patch_Distribution()