implement push support

Implement push support via Remote.push which is called with a single
refspec and raises GitError (with an appropriate message where
possible) if the push fails.

Note that local push to non-bare repository is currently not
supported by libgit2.

docs/remotes.rst

@@ -15,4 +15,5 @@ The Remote type
 .. autoattribute:: pygit2.Remote.refspec_count
 .. automethod:: pygit2.Remote.get_refspec
 .. automethod:: pygit2.Remote.fetch
+.. automethod:: pygit2.Remote.push
 .. automethod:: pygit2.Remote.save

src/remote.c

@@ -218,10 +218,76 @@ Remote_save(Remote *self, PyObject *args)
 }
 
 
+int
+push_status_foreach_callback(const char *ref, const char *msg, void *data)
+{
+    const char **msg_dst = (const char **)data;
+    if (msg != NULL && *msg_dst == NULL)
+        *msg_dst = msg;
+    return 0;
+}
+
+PyDoc_STRVAR(Remote_push__doc__,
+    "push(refspec)\n"
+    "\n"
+    "Push the given refspec to the remote.  Raises ``GitError`` on error.");
+
+PyObject *
+Remote_push(Remote *self, PyObject *args)
+{
+    git_push *push = NULL;
+    const char *refspec = NULL;
+    const char *msg = NULL;
+    int err;
+
+    if (!PyArg_ParseTuple(args, "s", &refspec))
+        return NULL;
+
+    err = git_push_new(&push, self->remote);
+    if (err < 0)
+        return Error_set(err);
+
+    err = git_push_add_refspec(push, refspec);
+    if (err < 0)
+        goto error;
+
+    err = git_push_finish(push);
+    if (err < 0)
+        goto error;
+
+    if (!git_push_unpack_ok(push)) {
+        git_push_free(push);
+        PyErr_SetString(GitError, "Remote failed to unpack objects");
+        return NULL;
+    }
+
+    err = git_push_status_foreach(push, push_status_foreach_callback, &msg);
+    if (err < 0)
+        goto error;
+    if (msg != NULL) {
+        git_push_free(push);
+        PyErr_SetString(GitError, msg);
+        return NULL;
+    }
+
+    err = git_push_update_tips(push);
+    if (err < 0)
+        goto error;
+
+    git_push_free(push);
+    Py_RETURN_NONE;
+
+error:
+    git_push_free(push);
+    return Error_set(err);
+}
+
+
 PyMethodDef Remote_methods[] = {
     METHOD(Remote, fetch, METH_NOARGS),
     METHOD(Remote, save, METH_NOARGS),
     METHOD(Remote, get_refspec, METH_O),
+    METHOD(Remote, push, METH_VARARGS),
     {NULL}
 };
 

test/test_remote.py

@@ -124,5 +124,45 @@ def test_fetch(self):
         self.assertEqual(stats['received_objects'], REMOTE_REPO_OBJECTS)
 
 
+class PushTestCase(unittest.TestCase):
+    def setUp(self):
+        self.origin_ctxtmgr = utils.TemporaryRepository(('git', 'testrepo.git'))
+        self.clone_ctxtmgr = utils.TemporaryRepository(('git', 'testrepo.git'))
+        self.origin = pygit2.Repository(self.origin_ctxtmgr.__enter__())
+        self.clone = pygit2.Repository(self.clone_ctxtmgr.__enter__())
+        self.remote = self.clone.create_remote('origin', self.origin.path)
+
+    def tearDown(self):
+        self.origin_ctxtmgr.__exit__(None, None, None)
+        self.clone_ctxtmgr.__exit__(None, None, None)
+
+    def test_push_fast_forward_commits_to_remote_succeeds(self):
+        tip = self.clone[self.clone.head.target]
+        oid = self.clone.create_commit(
+            'refs/heads/master', tip.author, tip.author, 'empty commit',
+            tip.tree.oid, [tip.oid]
+        )
+        self.remote.push('refs/heads/master')
+        self.assertEqual(self.origin[self.origin.head.target].oid, oid)
+
+    def test_push_when_up_to_date_succeeds(self):
+        self.remote.push('refs/heads/master')
+        origin_tip = self.origin[self.origin.head.target].oid
+        clone_tip = self.clone[self.clone.head.target].oid
+        self.assertEqual(origin_tip, clone_tip)
+
+    def test_push_non_fast_forward_commits_to_remote_fails(self):
+        tip = self.origin[self.origin.head.target]
+        oid = self.origin.create_commit(
+            'refs/heads/master', tip.author, tip.author, 'some commit',
+            tip.tree.oid, [tip.oid]
+        )
+        tip = self.clone[self.clone.head.target]
+        oid = self.clone.create_commit(
+            'refs/heads/master', tip.author, tip.author, 'other commit',
+            tip.tree.oid, [tip.oid]
+        )
+        self.assertRaises(pygit2.GitError, self.remote.push, 'refs/heads/master')
+
 if __name__ == '__main__':
     unittest.main()