storage: filesystem, Populate index before use. Fixes go-git#148

storage/filesystem/object.go

@@ -545,6 +545,9 @@ func (s *ObjectStorage) HashesWithPrefix(prefix []byte) ([]plumbing.Hash, error)
 
 	// TODO: This could be faster with some idxfile changes,
 	// or diving into the packfile.
+	if err := s.requireIndex(); err != nil {
+		return nil, err
+	}
 	for _, index := range s.index {
 		ei, err := index.Entries()
 		if err != nil {

storage/filesystem/object_test.go

@@ -406,6 +406,21 @@ func (s *FsSuite) TestHashesWithPrefix(c *C) {
 	c.Assert(hashes[0].String(), Equals, "f3dfe29d268303fc6e1bbce268605fc99573406e")
 }
 
+func (s *FsSuite) TestHashesWithPrefixFromPackfile(c *C) {
+	// Same setup as TestGetFromPackfile
+	fixtures.Basic().ByTag(".git").Test(c, func(f *fixtures.Fixture) {
+		fs := f.DotGit()
+		o := NewObjectStorage(dotgit.New(fs), cache.NewObjectLRUDefault())
+
+		expected := plumbing.NewHash("6ecf0ef2c2dffb796033e5a02219af86ec6584e5")
+		// Only pass the first 8 bytes
+		hashes, err := o.HashesWithPrefix(expected[:8])
+		c.Assert(err, IsNil)
+		c.Assert(hashes, HasLen, 1)
+		c.Assert(hashes[0], Equals, expected)
+	})
+}
+
 func BenchmarkPackfileIter(b *testing.B) {
 	defer fixtures.Clean()