From 35501acb0cea6a0c61e8a9e02b6331adbfed6f2f Mon Sep 17 00:00:00 2001
From: Viktor Dick <viktor.dick@perfact.de>
Date: Tue, 2 Oct 2018 11:28:48 +0200
Subject: [PATCH] Handle sorting of broken objects more gracefully.

---
 src/zope/sequencesort/ssort.py            |  4 ++
 src/zope/sequencesort/tests/test_ssort.py | 56 +++++++++++++++++++++++
 tox.ini                                   |  2 +-
 3 files changed, 61 insertions(+), 1 deletion(-)

diff --git a/src/zope/sequencesort/ssort.py b/src/zope/sequencesort/ssort.py
index 81496c8..3653066 100644
--- a/src/zope/sequencesort/ssort.py
+++ b/src/zope/sequencesort/ssort.py
@@ -256,6 +256,10 @@ def __call__(self, o1, o2):
             # if not multsort - i is 0, and the 0th element is the key
             c1, c2 = o1[i], o2[i]
             func, multiplier = self.sf_list[i][1:3]
+            if c1 is _Smallest:
+                return -1
+            elif c2 is _Smallest:
+                return 1
             n = func(c1, c2)
             if n:
                 return n * multiplier
diff --git a/src/zope/sequencesort/tests/test_ssort.py b/src/zope/sequencesort/tests/test_ssort.py
index 11f4b49..d4e01a5 100644
--- a/src/zope/sequencesort/tests/test_ssort.py
+++ b/src/zope/sequencesort/tests/test_ssort.py
@@ -17,6 +17,17 @@
 # pylint:disable=blacklisted-name
 # pylint:disable=protected-access
 
+# for sorting objects that are sortable but do not have any other attributes
+# or string-like behavior
+class _Broken(object):
+    def __lt__(self, other):
+        return True
+    def __eq__(self, other):
+        return other is self
+
+class _OK(object):
+    def __init__(self, _id):
+        self.id = _id
 
 class Test_sort(unittest.TestCase):
 
@@ -211,6 +222,51 @@ def myCmp(s1, s2):
             ),
             RES_W_CUSTOM_COMPARATOR)
 
+    def test_w_sort_broken(self):
+        _broken = _Broken()
+        _ok = _OK('test')
+        self.assertEqual(
+                self._callFUT([_ok, _broken]),
+                [_broken, _ok]
+                )
+
+    def test_w_sort_broken_with_key(self):
+        _broken = _Broken()
+        _ok = _OK('test')
+        self.assertEqual(
+                self._callFUT([_ok, _broken], [('id',),]),
+                [_broken, _ok]
+                )
+    
+    def test_w_sort_broken_with_key_locale(self):
+        # testing actual unicode literals to be sorted correctly has the
+        # problem that one can not assume that there is any locale actually
+        # installed on the system. But we can test if a broken object can be
+        # compared with a correct one even for a sorting that assumes stringy
+        # behavior
+        _broken = _Broken()
+        v1 = _OK(u'test')
+        self.assertEqual(
+                self._callFUT([v1,_broken], [('id','locale',),]),
+                [_broken, v1]
+                )
+        self.assertEqual(
+                self._callFUT([_broken,v1], [('id','locale',),]),
+                [_broken, v1]
+                )
+
+    def test_w_sort_broken_with_key_locale_nocase(self):
+        _broken = _Broken()
+        v1 = _OK(u'test')
+        self.assertEqual(
+                self._callFUT([v1,_broken], [('id','locale_nocase',),]),
+                [_broken, v1]
+                )
+        self.assertEqual(
+                self._callFUT([_broken,v1], [('id','locale_nocase',),]),
+                [_broken, v1]
+                )
+
 
 class Test_make_sortfunctions(unittest.TestCase):
 
diff --git a/tox.ini b/tox.ini
index 0651d0d..b704136 100644
--- a/tox.ini
+++ b/tox.ini
@@ -14,7 +14,7 @@ basepython =
     python3.6
 commands =
     coverage run -m zope.testrunner --test-path=src
-    coverage report --fail-under=100
+    coverage report --show-missing --fail-under=100
 deps =
     {[testenv]deps}
     coverage