object: implement peel()

This simplifies getting one type of object from a higher-level one as
well as accepting a commit-ish or tree-ish.

docs/objects.rst

@@ -81,6 +81,7 @@ This is the common interface for all Git objects:
 .. autoattribute:: pygit2.Object.id
 .. autoattribute:: pygit2.Object.type
 .. automethod:: pygit2.Object.read_raw
+.. automethod:: pygit2.Object.peel
 
 
 Blobs

src/object.c

@@ -127,6 +127,28 @@ Object_read_raw(Object *self)
     return aux;
 }
 
+PyDoc_STRVAR(Object_peel__doc__,
+  "peel(target_type) -> Object\n"
+  "\n"
+  "Peel the current object and returns the first object of the given type\n");
+
+PyObject *
+Object_peel(Object *self, PyObject *py_type)
+{
+    int type, err;
+    git_object *peeled;
+
+    type = PyLong_AsLong(py_type);
+    if (type == -1 && PyErr_Occurred())
+        return NULL;
+
+    err = git_object_peel(&peeled, self->obj, (git_otype)type);
+    if (err < 0)
+        return Error_set(err);
+
+    return wrap_object(peeled, self->repo);
+}
+
 PyGetSetDef Object_getseters[] = {
     GETTER(Object, oid),
     GETTER(Object, id),
@@ -137,6 +159,7 @@ PyGetSetDef Object_getseters[] = {
 
 PyMethodDef Object_methods[] = {
     METHOD(Object, read_raw, METH_NOARGS),
+    METHOD(Object, peel, METH_O),
     {NULL}
 };
 

test/test_object.py

@@ -0,0 +1,67 @@
+# -*- coding: UTF-8 -*-
+#
+# Copyright 2010-2014 The pygit2 contributors
+#
+# This file is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License, version 2,
+# as published by the Free Software Foundation.
+#
+# In addition to the permissions in the GNU General Public License,
+# the authors give you unlimited permission to link the compiled
+# version of this file into combinations with other programs,
+# and to distribute those combinations without any restriction
+# coming from the use of this file.  (The General Public License
+# restrictions do apply in other respects; for example, they cover
+# modification of the file, and distribution when not linked into
+# a combined executable.)
+#
+# This file is distributed in the hope that it will be useful, but
+# WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+# General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; see the file COPYING.  If not, write to
+# the Free Software Foundation, 51 Franklin Street, Fifth Floor,
+# Boston, MA 02110-1301, USA.
+
+"""Tests for Object objects."""
+
+from __future__ import absolute_import
+from __future__ import unicode_literals
+from os.path import dirname, join
+import unittest
+
+import pygit2
+from pygit2 import GIT_OBJ_TREE, GIT_OBJ_TAG
+from . import utils
+
+
+BLOB_SHA = 'a520c24d85fbfc815d385957eed41406ca5a860b'
+BLOB_CONTENT = """hello world
+hola mundo
+bonjour le monde
+""".encode()
+BLOB_NEW_CONTENT = b'foo bar\n'
+BLOB_FILE_CONTENT = b'bye world\n'
+
+class ObjectTest(utils.RepoTestCase):
+
+    def test_peel_commit(self):
+        # start by looking up the commit
+        commit_id = self.repo.lookup_reference('refs/heads/master').target
+        commit = self.repo[commit_id]
+        # and peel to the tree
+        tree = commit.peel(GIT_OBJ_TREE)
+
+        self.assertEqual(type(tree), pygit2.Tree)
+        self.assertEqual(str(tree.id), 'fd937514cb799514d4b81bb24c5fcfeb6472b245')
+
+    def test_invalid(self):
+        commit_id = self.repo.lookup_reference('refs/heads/master').target
+        commit = self.repo[commit_id]
+
+        self.assertRaises(ValueError, commit.peel, GIT_OBJ_TAG)
+
+if __name__ == '__main__':
+    unittest.main()