Index: accept adding either a path or an IndexEntry

A path is only useful if we have the file on the worktree. Passing an
IndexEntry allows us to add an entry with arbitrary attributes.

docs/working-copy.rst

@@ -22,6 +22,9 @@ Index write::
     >>> del index['path/to/file']          # git rm
     >>> index.write()                      # don't forget to save the changes
 
+Custom entries::
+   >>> entry = pygit2.IndexEntry('README.md', blob_id, blob_filemode)
+   >>> repo.index.add(entry)
 
 The Index type
 ====================

src/index.c

@@ -82,7 +82,7 @@ Index_traverse(Index *self, visitproc visit, void *arg)
 
 
 PyDoc_STRVAR(Index_add__doc__,
-  "add(path)\n"
+  "add([path|entry])\n"
   "\n"
   "Add or update an index entry from a file in disk.");
 
@@ -91,6 +91,16 @@ Index_add(Index *self, PyObject *args)
 {
     int err;
     const char *path;
+    IndexEntry *py_entry;
+
+    if (PyArg_ParseTuple(args, "O!", &IndexEntryType, &py_entry)) {
+        err = git_index_add(self->index, &py_entry->entry);
+        if (err < 0)
+            return Error_set(err);
+
+        Py_RETURN_NONE;
+    }
+    PyErr_Clear();
 
     if (!PyArg_ParseTuple(args, "s", &path))
         return NULL;

test/test_index.py

@@ -152,6 +152,15 @@ class IndexTest(utils.RepoTestCase):
         self.assertEqual(ign_entry.oid, entry.oid)
         self.assertEqual(pygit2.GIT_FILEMODE_BLOB_EXECUTABLE, entry.mode)
 
+class IndexEntryTest(utils.RepoTestCase):
+
+    def test_create_entry(self):
+        index = self.repo.index
+        hello_entry = index['hello.txt']
+        entry = pygit2.IndexEntry('README.md', hello_entry.oid, hello_entry.mode)
+        index.add(entry)
+        tree_id = index.write_tree()
+        self.assertEqual('60e769e57ae1d6a2ab75d8d253139e6260e1f912', str(tree_id))
 
 if __name__ == '__main__':
     unittest.main()