Add Repository.expand_id()

As we allow users of the library to use short strings, we must expand
them. This is however only available through a function in C. Expose
that function from the repository to allow python code to get a full id
from a short hex string.

src/repository.c

@@ -1433,6 +1433,24 @@ Repository_reset(Repository *self, PyObject* args)
     Py_RETURN_NONE;
 }
 
+PyDoc_STRVAR(Repository_expand_id__doc__,
+    "expand_id(hex) -> Oid\n"
+    "\n"
+    "Expand a string into a full Oid according to the objects in this repsitory.\n");
+
+PyObject *
+Repository_expand_id(Repository *self, PyObject *py_hex)
+{
+    git_oid oid;
+    int err;
+
+    err = py_oid_to_git_oid_expand(self->repo, py_hex, &oid);
+    if (err < 0)
+        return NULL;
+
+    return git_oid_to_python(&oid);
+}
+
 PyMethodDef Repository_methods[] = {
     METHOD(Repository, create_blob, METH_VARARGS),
     METHOD(Repository, create_blob_fromworkdir, METH_VARARGS),
@@ -1461,6 +1479,7 @@ PyMethodDef Repository_methods[] = {
     METHOD(Repository, listall_branches, METH_VARARGS),
     METHOD(Repository, create_branch, METH_VARARGS),
     METHOD(Repository, reset, METH_VARARGS),
+    METHOD(Repository, expand_id, METH_O),
     METHOD(Repository, _from_c, METH_VARARGS),
     METHOD(Repository, _disown, METH_NOARGS),
     {NULL}

test/test_repository.py

@@ -156,6 +156,11 @@ class RepositoryTest(utils.BareRepoTestCase):
             commit.message)
         self.assertRaises(ValueError, self.repo.__getitem__, too_short_prefix)
 
+    def test_expand_id(self):
+        commit_sha = '5fe808e8953c12735680c257f56600cb0de44b10'
+        expanded = self.repo.expand_id(commit_sha[:7])
+        self.assertEqual(commit_sha, expanded.hex)
+
     @unittest.skipIf(__pypy__ is not None, "skip refcounts checks in pypy")
     def test_lookup_commit_refcount(self):
         start = sys.getrefcount(self.repo)