Extract billy (#173)

* Extract billy

Billy is a new library directly extracted from go-git. It abstract
several storages systems in a filesystem interface.

More in github.com/src-d/billy

* Fix grouping in imports block

* Update billy to v1

* Re-remove fs_implementation example

1 files changed, 8 insertions, 7 deletions

diff --git a/storage/filesystem/internal/dotgit/writers.go b/storage/filesystem/internal/dotgit/writers.go
index 8e22a39..1cd893d 100644
--- a/storage/filesystem/internal/dotgit/writers.go
+++ b/storage/filesystem/internal/dotgit/writers.go
@@ -9,7 +9,8 @@ import (
 	"gopkg.in/src-d/go-git.v4/plumbing/format/idxfile"
 	"gopkg.in/src-d/go-git.v4/plumbing/format/objfile"
 	"gopkg.in/src-d/go-git.v4/plumbing/format/packfile"
-	"gopkg.in/src-d/go-git.v4/utils/fs"
+
+	"srcd.works/go-billy.v1"
 )
 
 // PackWriter is a io.Writer that generates the packfile index simultaneously,
@@ -21,15 +22,15 @@ import (
 type PackWriter struct {
 	Notify func(h plumbing.Hash, i idxfile.Idxfile)
 
-	fs       fs.Filesystem
-	fr, fw   fs.File
+	fs       billy.Filesystem
+	fr, fw   billy.File
 	synced   *syncedReader
 	checksum plumbing.Hash
 	index    idxfile.Idxfile
 	result   chan error
 }
 
-func newPackWrite(fs fs.Filesystem) (*PackWriter, error) {
+func newPackWrite(fs billy.Filesystem) (*PackWriter, error) {
 	fw, err := fs.TempFile(fs.Join(objectsPath, packPath), "tmp_pack_")
 	if err != nil {
 		return nil, err
@@ -248,11 +249,11 @@ func (s *syncedReader) Close() error {
 
 type ObjectWriter struct {
 	objfile.Writer
-	fs fs.Filesystem
-	f  fs.File
+	fs billy.Filesystem
+	f  billy.File
 }
 
-func newObjectWriter(fs fs.Filesystem) (*ObjectWriter, error) {
+func newObjectWriter(fs billy.Filesystem) (*ObjectWriter, error) {
 	f, err := fs.TempFile(fs.Join(objectsPath, packPath), "tmp_obj_")
 	if err != nil {
 		return nil, err