Add References.compress

This exports the functionality of `git_refdb_compress`, which is the
equivalent of `git pack-refs --all`.  This is useful to improve
performance in some contexts on repositories with a large number of
refs.

docs/references.rst

@@ -29,6 +29,9 @@ Example::
     # Delete a reference
     >>> repo.references.delete('refs/tags/version1')
 
+    # Pack loose references
+    >>> repo.references.compress()
+
 
 Functions
 ===================================

pygit2/repository.py

@@ -1269,6 +1269,9 @@ def __contains__(self, name):
     def objects(self):
         return self._repository.listall_reference_objects()
 
+    def compress(self):
+        return self._repository.compress_references()
+
 
 class Repository(BaseRepository):
     def __init__(self, path, *args, **kwargs):

src/repository.c

@@ -1407,6 +1407,31 @@ Repository_create_reference_symbolic(Repository *self,  PyObject *args,
     return wrap_reference(c_reference, self);
 }
 
+PyDoc_STRVAR(Repository_compress_references__doc__,
+  "compress_references()\n"
+  "\n"
+  "Suggest that the repository compress or optimize its references.\n"
+  "This mechanism is implementation-specific.  For on-disk reference\n"
+  "databases, for example, this may pack all loose references.");
+
+PyObject *
+Repository_compress_references(Repository *self)
+{
+    git_refdb *refdb;
+    int err;
+
+    err = git_repository_refdb(&refdb, self->repo);
+    if (err < 0)
+        return Error_set(err);
+
+    err = git_refdb_compress(refdb);
+
+    git_refdb_free(refdb);
+    if (err < 0)
+        return Error_set(err);
+    Py_RETURN_NONE;
+}
+
 PyDoc_STRVAR(Repository_status__doc__,
   "status() -> {str: int}\n"
   "\n"
@@ -1874,6 +1899,7 @@ PyMethodDef Repository_methods[] = {
     METHOD(Repository, apply, METH_O),
     METHOD(Repository, create_reference_direct, METH_VARARGS),
     METHOD(Repository, create_reference_symbolic, METH_VARARGS),
+    METHOD(Repository, compress_references, METH_NOARGS),
     METHOD(Repository, listall_references, METH_NOARGS),
     METHOD(Repository, listall_reference_objects, METH_NOARGS),
     METHOD(Repository, listall_submodules, METH_NOARGS),

test/test_refs.py

@@ -25,6 +25,8 @@
 
 """Tests for reference objects."""
 
+import os
+
 import pytest
 
 from pygit2 import GIT_REF_OID, GIT_REF_SYMBOLIC, Signature
@@ -238,6 +240,19 @@ def test_equality(self):
         assert ref1 != ref3
         assert not ref1 == ref3
 
+    def test_compress(self):
+        repo = self.repo
+        packed_refs_file = os.path.join(self.repo_path, '.git', 'packed-refs')
+        assert not os.path.exists(packed_refs_file)
+        old_refs = [(ref.name, ref.target.hex)
+                    for ref in repo.references.objects]
+
+        repo.references.compress()
+        assert os.path.exists(packed_refs_file)
+        new_refs = [(ref.name, ref.target.hex)
+                    for ref in repo.references.objects]
+        assert old_refs == new_refs
+
 class ReferencesTest(utils.RepoTestCase):
     def test_list_all_reference_objects(self):
         repo = self.repo