TreeEntry: compare ids when two entrie sort equally

The function we were using `git_tree_entry_cmp()` is only meant for
git-compatible sorting in a tree and thus does not take the id into
account. This is however important in order to keep value equality. In
order to avoid issues with assymetry, we compare the id any time when
two entries are equal according to their position in a tree.

src/tree.c

@@ -87,10 +87,20 @@ TreeEntry_oid__get__(TreeEntry *self)
     return TreeEntry_id__get__(self);
 }
 
+static int
+compare_ids(TreeEntry *a, TreeEntry *b)
+{
+    const git_oid *id_a, *id_b;
+    id_a = git_tree_entry_id(a->entry);
+    id_b = git_tree_entry_id(b->entry);
+    return git_oid_cmp(id_a, id_b);
+}
+
 PyObject *
 TreeEntry_richcompare(PyObject *a, PyObject *b, int op)
 {
     PyObject *res;
+    TreeEntry *ta, *tb;
     int cmp;
 
     /* We only support comparing to another tree entry */
@@ -99,7 +109,14 @@ TreeEntry_richcompare(PyObject *a, PyObject *b, int op)
         return Py_NotImplemented;
     }
 
-    cmp =git_tree_entry_cmp(((TreeEntry*)a)->entry, ((TreeEntry*)b)->entry);
+    ta = (TreeEntry *) a;
+    tb = (TreeEntry *) b;
+
+    /* This is sorting order, if they sort equally, we still need to compare the ids */
+    cmp = git_tree_entry_cmp(ta->entry, tb->entry);
+    if (cmp == 0)
+        cmp = compare_ids(ta, tb);
+
     switch (op) {
         case Py_LT:
             res = (cmp <= 0) ? Py_True: Py_False;
@@ -147,7 +164,6 @@ PyGetSetDef TreeEntry_getseters[] = {
     {NULL}
 };
 
-
 PyDoc_STRVAR(TreeEntry__doc__, "TreeEntry objects.");
 
 PyTypeObject TreeEntryType = {

test/test_tree.py

@@ -32,6 +32,7 @@ from __future__ import unicode_literals
 import operator
 import unittest
 
+from pygit2 import TreeEntry
 from . import utils
 
 
@@ -71,6 +72,18 @@ class TreeTest(utils.BareRepoTestCase):
         self.assertTreeEntryEqual(tree['c/d'], sha, 'd', 0o0100644)
         self.assertRaisesWithArg(KeyError, 'ab/cd', lambda: tree['ab/cd'])
 
+    def test_equality(self):
+        tree_a = self.repo['18e2d2e9db075f9eb43bcb2daa65a2867d29a15e']
+        tree_b = self.repo['2ad1d3456c5c4a1c9e40aeeddb9cd20b409623c8']
+
+        self.assertNotEqual(tree_a['a'], tree_b['a'])
+        self.assertNotEqual(tree_a['a'], tree_b['b'])
+        self.assertEqual(tree_a['b'], tree_b['b'])
+
+    def test_sorting(self):
+        tree_a = self.repo['18e2d2e9db075f9eb43bcb2daa65a2867d29a15e']
+        self.assertEqual(list(tree_a), sorted(reversed(list(tree_a))))
+        self.assertNotEqual(list(tree_a), reversed(list(tree_a)))
 
     def test_read_subtree(self):
         tree = self.repo[TREE_SHA]