*: upgrade to go-billy.v3, merge

31 files changed, 148 insertions, 134 deletions

diff --git a/appveyor.yml b/appveyor.yml
index f36ebe7..160616b 100644
--- a/appveyor.yml
+++ b/appveyor.yml
@@ -11,10 +11,9 @@ environment:
   GOPATH: c:\gopath
 
 install:
-  - set PATH=%GOPATH%\bin;c:\go\bin;%PATH%
+  - set PATH=%GOPATH%\bin;c:\go\bin;"C:\Program Files\Git\mingw64\bin";%PATH%
   - go version
   - go get -v -t ./...
-
   - git config --global user.email "travis@example.com"
   - git config --global user.name "Travis CI
 
diff --git a/common_test.go b/common_test.go
index e1a2a0f..3f5364c 100644
--- a/common_test.go
+++ b/common_test.go
@@ -11,8 +11,8 @@ import (
 
 	"github.com/src-d/go-git-fixtures"
 	. "gopkg.in/check.v1"
-	"gopkg.in/src-d/go-billy.v2/memfs"
-	"gopkg.in/src-d/go-billy.v2/osfs"
+	"gopkg.in/src-d/go-billy.v3/memfs"
+	"gopkg.in/src-d/go-billy.v3/osfs"
 )
 
 func Test(t *testing.T) { TestingT(t) }
@@ -42,7 +42,7 @@ func (s *BaseSuite) buildBasicRepository(c *C) {
 }
 
 func (s *BaseSuite) NewRepository(f *fixtures.Fixture) *Repository {
-	fs := osfs.New(f.DotGit().Base())
+	fs := osfs.New(f.DotGit().Root())
 	st, err := filesystem.NewStorage(fs)
 	if err != nil {
 		panic(err)
@@ -94,7 +94,7 @@ func (s *BaseSuite) GetBasicLocalRepositoryURL() string {
 }
 
 func (s *BaseSuite) GetLocalRepositoryURL(f *fixtures.Fixture) string {
-	return f.DotGit().Base()
+	return f.DotGit().Root()
 }
 
 type SuiteCommon struct{}
diff --git a/example_test.go b/example_test.go
index abcbec7..585b38a 100644
--- a/example_test.go
+++ b/example_test.go
@@ -13,7 +13,7 @@ import (
 	"gopkg.in/src-d/go-git.v4/plumbing"
 	"gopkg.in/src-d/go-git.v4/storage/memory"
 
-	"gopkg.in/src-d/go-billy.v2/memfs"
+	"gopkg.in/src-d/go-billy.v3/memfs"
 )
 
 func ExampleClone() {
diff --git a/plumbing/format/packfile/decoder_test.go b/plumbing/format/packfile/decoder_test.go
index f081fd7..f1e2ed7 100644
--- a/plumbing/format/packfile/decoder_test.go
+++ b/plumbing/format/packfile/decoder_test.go
@@ -3,7 +3,7 @@ package packfile_test
 import (
 	"io"
 
-	"gopkg.in/src-d/go-billy.v2/memfs"
+	"gopkg.in/src-d/go-billy.v3/memfs"
 
 	"github.com/src-d/go-git-fixtures"
 	"gopkg.in/src-d/go-git.v4/plumbing"
diff --git a/plumbing/transport/file/receive_pack_test.go b/plumbing/transport/file/receive_pack_test.go
index 5bbad44..ab21aea 100644
--- a/plumbing/transport/file/receive_pack_test.go
+++ b/plumbing/transport/file/receive_pack_test.go
@@ -23,11 +23,11 @@ func (s *ReceivePackSuite) SetUpSuite(c *C) {
 
 func (s *ReceivePackSuite) SetUpTest(c *C) {
 	fixture := fixtures.Basic().One()
-	path := fixture.DotGit().Base()
+	path := fixture.DotGit().Root()
 	s.Endpoint = prepareRepo(c, path)
 
 	fixture = fixtures.ByTag("empty").One()
-	path = fixture.DotGit().Base()
+	path = fixture.DotGit().Root()
 	s.EmptyEndpoint = prepareRepo(c, path)
 
 	s.NonExistentEndpoint = prepareRepo(c, "/non-existent")
diff --git a/plumbing/transport/file/server_test.go b/plumbing/transport/file/server_test.go
index 176d6ee..ee72282 100644
--- a/plumbing/transport/file/server_test.go
+++ b/plumbing/transport/file/server_test.go
@@ -24,10 +24,10 @@ func (s *ServerSuite) SetUpSuite(c *C) {
 	s.RemoteName = "test"
 
 	fixture := fixtures.Basic().One()
-	s.SrcPath = fixture.DotGit().Base()
+	s.SrcPath = fixture.DotGit().Root()
 
 	fixture = fixtures.ByTag("empty").One()
-	s.DstPath = fixture.DotGit().Base()
+	s.DstPath = fixture.DotGit().Root()
 
 	cmd := exec.Command("git", "remote", "add", s.RemoteName, s.DstPath)
 	cmd.Dir = s.SrcPath
diff --git a/plumbing/transport/file/upload_pack_test.go b/plumbing/transport/file/upload_pack_test.go
index f013683..f894935 100644
--- a/plumbing/transport/file/upload_pack_test.go
+++ b/plumbing/transport/file/upload_pack_test.go
@@ -24,13 +24,13 @@ func (s *UploadPackSuite) SetUpSuite(c *C) {
 	s.UploadPackSuite.Client = DefaultClient
 
 	fixture := fixtures.Basic().One()
-	path := fixture.DotGit().Base()
+	path := fixture.DotGit().Root()
 	ep, err := transport.NewEndpoint(path)
 	c.Assert(err, IsNil)
 	s.Endpoint = ep
 
 	fixture = fixtures.ByTag("empty").One()
-	path = fixture.DotGit().Base()
+	path = fixture.DotGit().Root()
 	ep, err = transport.NewEndpoint(path)
 	c.Assert(err, IsNil)
 	s.EmptyEndpoint = ep
@@ -74,6 +74,7 @@ func (s *UploadPackSuite) TestNonExistentCommand(c *C) {
 	cmd := "/non-existent-git"
 	client := NewClient(cmd, cmd)
 	session, err := client.NewUploadPackSession(s.Endpoint, s.EmptyAuth)
-	c.Assert(err, ErrorMatches, ".*no such file or directory.*")
+	// Error message is OS-dependant, so do a broad check
+	c.Assert(err, ErrorMatches, ".*file.*")
 	c.Assert(session, IsNil)
 }
diff --git a/plumbing/transport/git/receive_pack_test.go b/plumbing/transport/git/receive_pack_test.go
index d73966e..326ef1b 100644
--- a/plumbing/transport/git/receive_pack_test.go
+++ b/plumbing/transport/git/receive_pack_test.go
@@ -43,7 +43,7 @@ func (s *ReceivePackSuite) SetUpTest(c *C) {
 	err = os.MkdirAll(interpolatedBase, 0755)
 	c.Assert(err, IsNil)
 
-	dotgit := fixtures.Basic().One().DotGit().Base()
+	dotgit := fixtures.Basic().One().DotGit().Root()
 	prepareRepo(c, dotgit)
 	err = os.Rename(dotgit, filepath.Join(interpolatedBase, "basic.git"))
 	c.Assert(err, IsNil)
@@ -52,7 +52,7 @@ func (s *ReceivePackSuite) SetUpTest(c *C) {
 	c.Assert(err, IsNil)
 	s.ReceivePackSuite.Endpoint = ep
 
-	dotgit = fixtures.ByTag("empty").One().DotGit().Base()
+	dotgit = fixtures.ByTag("empty").One().DotGit().Root()
 	prepareRepo(c, dotgit)
 	err = os.Rename(dotgit, filepath.Join(interpolatedBase, "empty.git"))
 	c.Assert(err, IsNil)
diff --git a/plumbing/transport/server/loader.go b/plumbing/transport/server/loader.go
index 386c2f0..d4eccd4 100644
--- a/plumbing/transport/server/loader.go
+++ b/plumbing/transport/server/loader.go
@@ -5,8 +5,8 @@ import (
 	"gopkg.in/src-d/go-git.v4/plumbing/transport"
 	"gopkg.in/src-d/go-git.v4/storage/filesystem"
 
-	"gopkg.in/src-d/go-billy.v2"
-	"gopkg.in/src-d/go-billy.v2/osfs"
+	"gopkg.in/src-d/go-billy.v3"
+	"gopkg.in/src-d/go-billy.v3/osfs"
 )
 
 // DefaultLoader is a filesystem loader ignoring host and resolving paths to /.
@@ -34,7 +34,11 @@ func NewFilesystemLoader(base billy.Filesystem) Loader {
 // storer for it. Returns transport.ErrRepositoryNotFound if a repository does
 // not exist in the given path.
 func (l *fsLoader) Load(ep transport.Endpoint) (storer.Storer, error) {
-	fs := l.base.Dir(ep.Path())
+	fs, err := l.base.Chroot(ep.Path())
+	if err != nil {
+		return nil, err
+	}
+
 	if _, err := fs.Stat("config"); err != nil {
 		return nil, transport.ErrRepositoryNotFound
 	}
diff --git a/plumbing/transport/server/server_test.go b/plumbing/transport/server/server_test.go
index 6a64674..0f7201c 100644
--- a/plumbing/transport/server/server_test.go
+++ b/plumbing/transport/server/server_test.go
@@ -1,7 +1,6 @@
 package server_test
 
 import (
-	"fmt"
 	"testing"
 
 	"github.com/src-d/go-git-fixtures"
@@ -16,8 +15,6 @@ import (
 
 func Test(t *testing.T) { TestingT(t) }
 
-const inprocScheme = "inproc"
-
 type BaseSuite struct {
 	fixtures.Suite
 	loader       server.MapLoader
@@ -29,15 +26,15 @@ func (s *BaseSuite) SetUpSuite(c *C) {
 	s.Suite.SetUpSuite(c)
 	s.loader = server.MapLoader{}
 	s.client = server.NewServer(s.loader)
-	s.clientBackup = client.Protocols[inprocScheme]
-	client.Protocols[inprocScheme] = s.client
+	s.clientBackup = client.Protocols["file"]
+	client.Protocols["file"] = s.client
 }
 
 func (s *BaseSuite) TearDownSuite(c *C) {
 	if s.clientBackup == nil {
-		delete(client.Protocols, inprocScheme)
+		delete(client.Protocols, "file")
 	} else {
-		client.Protocols[inprocScheme] = s.clientBackup
+		client.Protocols["file"] = s.clientBackup
 	}
 }
 
@@ -46,9 +43,8 @@ func (s *BaseSuite) prepareRepositories(c *C, basic *transport.Endpoint,
 
 	f := fixtures.Basic().One()
 	fs := f.DotGit()
-	path := fs.Base()
-	url := fmt.Sprintf("%s://%s", inprocScheme, path)
-	ep, err := transport.NewEndpoint(url)
+	path := fs.Root()
+	ep, err := transport.NewEndpoint(path)
 	c.Assert(err, IsNil)
 	*basic = ep
 	sto, err := filesystem.NewStorage(fs)
@@ -56,15 +52,13 @@ func (s *BaseSuite) prepareRepositories(c *C, basic *transport.Endpoint,
 	s.loader[ep.String()] = sto
 
 	path = "/empty.git"
-	url = fmt.Sprintf("%s://%s", inprocScheme, path)
-	ep, err = transport.NewEndpoint(url)
+	ep, err = transport.NewEndpoint(path)
 	c.Assert(err, IsNil)
 	*empty = ep
 	s.loader[ep.String()] = memory.NewStorage()
 
 	path = "/non-existent.git"
-	url = fmt.Sprintf("%s://%s", inprocScheme, path)
-	ep, err = transport.NewEndpoint(url)
+	ep, err = transport.NewEndpoint(path)
 	c.Assert(err, IsNil)
 	*nonExistent = ep
 }
diff --git a/references_test.go b/references_test.go
index 050f169..3697949 100644
--- a/references_test.go
+++ b/references_test.go
@@ -292,7 +292,7 @@ func (s *ReferencesSuite) TestObjectNotFoundError(c *C) {
 	h1 := plumbing.NewHash("af2d6a6954d532f8ffb47615169c8fdf9d383a1a")
 	hParent := plumbing.NewHash("1669dce138d9b841a518c64b10914d88f5e488ea")
 
-	url := fixtures.ByURL("https://github.com/git-fixtures/basic.git").One().DotGit().Base()
+	url := fixtures.ByURL("https://github.com/git-fixtures/basic.git").One().DotGit().Root()
 	storer := memory.NewStorage()
 	r, err := Clone(storer, nil, &CloneOptions{
 		URL: url,
diff --git a/remote_test.go b/remote_test.go
index 8b2f71c..78339d4 100644
--- a/remote_test.go
+++ b/remote_test.go
@@ -15,7 +15,7 @@ import (
 	"gopkg.in/src-d/go-git.v4/storage/memory"
 
 	. "gopkg.in/check.v1"
-	"gopkg.in/src-d/go-billy.v2/osfs"
+	"gopkg.in/src-d/go-billy.v3/osfs"
 )
 
 type RemoteSuite struct {
@@ -214,7 +214,7 @@ func (s *RemoteSuite) TestPushToEmptyRepository(c *C) {
 	c.Assert(err, IsNil)
 
 	dstFs := fixtures.ByTag("empty").One().DotGit()
-	url := dstFs.Base()
+	url := dstFs.Root()
 
 	r := newRemote(sto, &config.RemoteConfig{
 		Name: DefaultRemoteName,
@@ -254,7 +254,7 @@ func (s *RemoteSuite) TestPushTags(c *C) {
 	c.Assert(err, IsNil)
 
 	dstFs := fixtures.ByTag("empty").One().DotGit()
-	url := dstFs.Base()
+	url := dstFs.Root()
 
 	r := newRemote(sto, &config.RemoteConfig{
 		Name: DefaultRemoteName,
@@ -297,7 +297,7 @@ func (s *RemoteSuite) TestPushNoErrAlreadyUpToDate(c *C) {
 	f := fixtures.Basic().One()
 	sto, err := filesystem.NewStorage(f.DotGit())
 	c.Assert(err, IsNil)
-	url := f.DotGit().Base()
+	url := f.DotGit().Root()
 	r := newRemote(sto, &config.RemoteConfig{
 		Name: DefaultRemoteName,
 		URL:  url,
@@ -319,7 +319,7 @@ func (s *RemoteSuite) TestPushRejectNonFastForward(c *C) {
 	dstSto, err := filesystem.NewStorage(dstFs)
 	c.Assert(err, IsNil)
 
-	url := dstFs.Base()
+	url := dstFs.Root()
 	r := newRemote(sto, &config.RemoteConfig{
 		Name: DefaultRemoteName,
 		URL:  url,
@@ -348,7 +348,7 @@ func (s *RemoteSuite) TestPushForce(c *C) {
 	dstSto, err := filesystem.NewStorage(dstFs)
 	c.Assert(err, IsNil)
 
-	url := dstFs.Base()
+	url := dstFs.Root()
 	r := newRemote(sto, &config.RemoteConfig{
 		Name: DefaultRemoteName,
 		URL:  url,
@@ -377,7 +377,7 @@ func (s *RemoteSuite) TestPushNewReference(c *C) {
 	dstSto, err := filesystem.NewStorage(dstFs)
 	c.Assert(err, IsNil)
 
-	url := dstFs.Base()
+	url := dstFs.Root()
 	r := newRemote(sto, &config.RemoteConfig{
 		Name: DefaultRemoteName,
 		URL:  url,
diff --git a/repository.go b/repository.go
index a3e441b..a60f3ef 100644
--- a/repository.go
+++ b/repository.go
@@ -17,8 +17,8 @@ import (
 	"gopkg.in/src-d/go-git.v4/storage/filesystem"
 	"gopkg.in/src-d/go-git.v4/utils/ioutil"
 
-	"gopkg.in/src-d/go-billy.v2"
-	"gopkg.in/src-d/go-billy.v2/osfs"
+	"gopkg.in/src-d/go-billy.v3"
+	"gopkg.in/src-d/go-billy.v3/osfs"
 )
 
 var (
@@ -92,11 +92,6 @@ func setWorktreeAndStoragePaths(r *Repository, worktree billy.Filesystem) error
 		return nil
 	}
 
-	_, isOS := fs.Filesystem().(*osfs.OS)
-	if !isOS {
-		return nil
-	}
-
 	if err := createDotGitFile(worktree, fs.Filesystem()); err != nil {
 		return err
 	}
@@ -105,9 +100,9 @@ func setWorktreeAndStoragePaths(r *Repository, worktree billy.Filesystem) error
 }
 
 func createDotGitFile(worktree, storage billy.Filesystem) error {
-	path, err := filepath.Rel(worktree.Base(), storage.Base())
+	path, err := filepath.Rel(worktree.Root(), storage.Root())
 	if err != nil {
-		path = storage.Base()
+		path = storage.Root()
 	}
 
 	if path == ".git" {
@@ -126,9 +121,9 @@ func createDotGitFile(worktree, storage billy.Filesystem) error {
 }
 
 func setConfigWorktree(r *Repository, worktree, storage billy.Filesystem) error {
-	path, err := filepath.Rel(storage.Base(), worktree.Base())
+	path, err := filepath.Rel(storage.Root(), worktree.Root())
 	if err != nil {
-		path = worktree.Base()
+		path = worktree.Root()
 	}
 
 	if path == ".." {
@@ -194,7 +189,7 @@ func PlainInit(path string, isBare bool) (*Repository, error) {
 		dot = osfs.New(path)
 	} else {
 		wt = osfs.New(path)
-		dot = wt.Dir(".git")
+		dot, _ = wt.Chroot(".git")
 	}
 
 	s, err := filesystem.NewStorage(dot)
@@ -209,7 +204,7 @@ func PlainInit(path string, isBare bool) (*Repository, error) {
 // repository is bare or a normal one. If the path doesn't contain a valid
 // repository ErrRepositoryNotExists is returned
 func PlainOpen(path string) (*Repository, error) {
-	dot, wt, err := dotGitToFilesystems(path)
+	dot, wt, err := dotGitToOSFilesystems(path)
 	if err != nil {
 		return nil, err
 	}
@@ -230,7 +225,7 @@ func PlainOpen(path string) (*Repository, error) {
 	return Open(s, wt)
 }
 
-func dotGitToFilesystems(path string) (dot, wt billy.Filesystem, err error) {
+func dotGitToOSFilesystems(path string) (dot, wt billy.Filesystem, err error) {
 	fs := osfs.New(path)
 	fi, err := fs.Stat(".git")
 	if err != nil {
@@ -242,10 +237,11 @@ func dotGitToFilesystems(path string) (dot, wt billy.Filesystem, err error) {
 	}
 
 	if fi.IsDir() {
-		return fs.Dir(".git"), fs, nil
+		dot, err = fs.Chroot(".git")
+		return dot, fs, err
 	}
 
-	dot, err = dotGitFileToFilesystem(fs)
+	dot, err = dotGitFileToOSFilesystem(path, fs)
 	if err != nil {
 		return nil, nil, err
 	}
@@ -253,7 +249,7 @@ func dotGitToFilesystems(path string) (dot, wt billy.Filesystem, err error) {
 	return dot, fs, nil
 }
 
-func dotGitFileToFilesystem(fs billy.Filesystem) (billy.Filesystem, error) {
+func dotGitFileToOSFilesystem(path string, fs billy.Filesystem) (billy.Filesystem, error) {
 	var err error
 
 	f, err := fs.Open(".git")
@@ -279,7 +275,7 @@ func dotGitFileToFilesystem(fs billy.Filesystem) (billy.Filesystem, error) {
 		return osfs.New(gitdir), nil
 	}
 
-	return fs.Dir(gitdir), err
+	return osfs.New(fs.Join(path, gitdir)), nil
 }
 
 // PlainClone a repository into the path with the given options, isBare defines
diff --git a/repository_test.go b/repository_test.go
index deb3f58..f622007 100644
--- a/repository_test.go
+++ b/repository_test.go
@@ -18,8 +18,8 @@ import (
 	"gopkg.in/src-d/go-git.v4/storage/memory"
 
 	. "gopkg.in/check.v1"
-	"gopkg.in/src-d/go-billy.v2/memfs"
-	"gopkg.in/src-d/go-billy.v2/osfs"
+	"gopkg.in/src-d/go-billy.v3/memfs"
+	"gopkg.in/src-d/go-billy.v3/osfs"
 )
 
 type RepositorySuite struct {
@@ -44,23 +44,25 @@ func (s *RepositorySuite) TestInitNonStandardDotGit(c *C) {
 	c.Assert(os.RemoveAll(dir), IsNil)
 
 	fs := osfs.New(dir)
-	storage, err := filesystem.NewStorage(fs.Dir("storage"))
+	dot, _ := fs.Chroot("storage")
+	storage, err := filesystem.NewStorage(dot)
 	c.Assert(err, IsNil)
 
-	r, err := Init(storage, fs.Dir("worktree"))
+	wt, _ := fs.Chroot("worktree")
+	r, err := Init(storage, wt)
 	c.Assert(err, IsNil)
 	c.Assert(r, NotNil)
 
-	f, err := fs.Open("worktree/.git")
+	f, err := fs.Open(fs.Join("worktree", ".git"))
 	c.Assert(err, IsNil)
 
 	all, err := ioutil.ReadAll(f)
 	c.Assert(err, IsNil)
-	c.Assert(string(all), Equals, "gitdir: ../storage\n")
+	c.Assert(string(all), Equals, fmt.Sprintf("gitdir: %s\n", filepath.Join("..", "storage")))
 
 	cfg, err := r.Config()
 	c.Assert(err, IsNil)
-	c.Assert(cfg.Core.Worktree, Equals, "../worktree")
+	c.Assert(cfg.Core.Worktree, Equals, filepath.Join("..", "worktree"))
 }
 
 func (s *RepositorySuite) TestInitStandardDotGit(c *C) {
@@ -69,7 +71,8 @@ func (s *RepositorySuite) TestInitStandardDotGit(c *C) {
 	c.Assert(os.RemoveAll(dir), IsNil)
 
 	fs := osfs.New(dir)
-	storage, err := filesystem.NewStorage(fs.Dir(".git"))
+	dot, _ := fs.Chroot(".git")
+	storage, err := filesystem.NewStorage(dot)
 	c.Assert(err, IsNil)
 
 	r, err := Init(storage, fs)
@@ -386,7 +389,7 @@ func (s *RepositorySuite) TestPlainCloneWithRecurseSubmodules(c *C) {
 	c.Assert(err, IsNil)
 	defer os.RemoveAll(dir)
 
-	path := fixtures.ByTag("submodule").One().Worktree().Base()
+	path := fixtures.ByTag("submodule").One().Worktree().Root()
 	r, err := PlainClone(dir, false, &CloneOptions{
 		URL:               path,
 		RecurseSubmodules: DefaultSubmoduleRecursionDepth,
@@ -669,7 +672,7 @@ func (s *RepositorySuite) TestPullProgress(c *C) {
 }
 
 func (s *RepositorySuite) TestPullProgressWithRecursion(c *C) {
-	path := fixtures.ByTag("submodule").One().Worktree().Base()
+	path := fixtures.ByTag("submodule").One().Worktree().Root()
 
 	dir, err := ioutil.TempDir("", "plain-clone-submodule")
 	c.Assert(err, IsNil)
@@ -691,7 +694,7 @@ func (s *RepositorySuite) TestPullProgressWithRecursion(c *C) {
 }
 
 func (s *RepositorySuite) TestPullAdd(c *C) {
-	path := fixtures.Basic().ByTag("worktree").One().Worktree().Base()
+	path := fixtures.Basic().ByTag("worktree").One().Worktree().Root()
 
 	r, err := Clone(memory.NewStorage(), nil, &CloneOptions{
 		URL: filepath.Join(path, ".git"),
@@ -729,7 +732,7 @@ func (s *RepositorySuite) TestPushToEmptyRepository(c *C) {
 	c.Assert(err, IsNil)
 
 	dstFs := fixtures.ByTag("empty").One().DotGit()
-	url := dstFs.Base()
+	url := dstFs.Root()
 
 	r, err := Open(sto, srcFs)
 	c.Assert(err, IsNil)
diff --git a/storage/filesystem/config_test.go b/storage/filesystem/config_test.go
index b2879b3..1b812e6 100644
--- a/storage/filesystem/config_test.go
+++ b/storage/filesystem/config_test.go
@@ -8,7 +8,7 @@ import (
 	"gopkg.in/src-d/go-git.v4/storage/filesystem/internal/dotgit"
 
 	. "gopkg.in/check.v1"
-	"gopkg.in/src-d/go-billy.v2/osfs"
+	"gopkg.in/src-d/go-billy.v3/osfs"
 )
 
 type ConfigSuite struct {
diff --git a/storage/filesystem/internal/dotgit/dotgit.go b/storage/filesystem/internal/dotgit/dotgit.go
index 1af64ab..c48f24c 100644
--- a/storage/filesystem/internal/dotgit/dotgit.go
+++ b/storage/filesystem/internal/dotgit/dotgit.go
@@ -12,7 +12,7 @@ import (
 	"gopkg.in/src-d/go-git.v4/plumbing"
 	"gopkg.in/src-d/go-git.v4/utils/ioutil"
 
-	"gopkg.in/src-d/go-billy.v2"
+	"gopkg.in/src-d/go-billy.v3"
 )
 
 const (
@@ -357,7 +357,7 @@ func (d *DotGit) rewritePackedRefsWithoutRef(name plumbing.ReferenceName) (err e
 		return err
 	}
 
-	tmpPath := tmp.Filename()
+	tmpPath := tmp.Name()
 	defer ioutil.CheckClose(tmp, &err)
 	defer d.fs.Remove(tmpPath)
 
@@ -413,11 +413,11 @@ func (d *DotGit) processLine(line string) (*plumbing.Reference, error) {
 }
 
 func (d *DotGit) addRefsFromRefDir(refs *[]*plumbing.Reference) error {
-	return d.walkReferencesTree(refs, refsPath)
+	return d.walkReferencesTree(refs, []string{refsPath})
 }
 
-func (d *DotGit) walkReferencesTree(refs *[]*plumbing.Reference, relPath string) error {
-	files, err := d.fs.ReadDir(relPath)
+func (d *DotGit) walkReferencesTree(refs *[]*plumbing.Reference, relPath []string) error {
+	files, err := d.fs.ReadDir(d.fs.Join(relPath...))
 	if err != nil {
 		if os.IsNotExist(err) {
 			return nil
@@ -427,7 +427,7 @@ func (d *DotGit) walkReferencesTree(refs *[]*plumbing.Reference, relPath string)
 	}
 
 	for _, f := range files {
-		newRelPath := d.fs.Join(relPath, f.Name())
+		newRelPath := append(append([]string(nil), relPath...), f.Name())
 		if f.IsDir() {
 			if err = d.walkReferencesTree(refs, newRelPath); err != nil {
 				return err
@@ -436,7 +436,7 @@ func (d *DotGit) walkReferencesTree(refs *[]*plumbing.Reference, relPath string)
 			continue
 		}
 
-		ref, err := d.readReferenceFile(".", newRelPath)
+		ref, err := d.readReferenceFile(".", strings.Join(newRelPath, "/"))
 		if err != nil {
 			return err
 		}
@@ -463,9 +463,8 @@ func (d *DotGit) addRefFromHEAD(refs *[]*plumbing.Reference) error {
 	return nil
 }
 
-func (d *DotGit) readReferenceFile(refsPath, refFile string) (ref *plumbing.Reference, err error) {
-	path := d.fs.Join(refsPath, refFile)
-
+func (d *DotGit) readReferenceFile(path, name string) (ref *plumbing.Reference, err error) {
+	path = d.fs.Join(path, d.fs.Join(strings.Split(name, "/")...))
 	f, err := d.fs.Open(path)
 	if err != nil {
 		return nil, err
@@ -478,12 +477,12 @@ func (d *DotGit) readReferenceFile(refsPath, refFile string) (ref *plumbing.Refe
 	}
 
 	line := strings.TrimSpace(string(b))
-	return plumbing.NewReferenceFromStrings(refFile, line), nil
+	return plumbing.NewReferenceFromStrings(name, line), nil
 }
 
 // Module return a billy.Filesystem poiting to the module folder
-func (d *DotGit) Module(name string) billy.Filesystem {
-	return d.fs.Dir(d.fs.Join(modulePath, name))
+func (d *DotGit) Module(name string) (billy.Filesystem, error) {
+	return d.fs.Chroot(d.fs.Join(modulePath, name))
 }
 
 func isHex(s string) bool {
diff --git a/storage/filesystem/internal/dotgit/dotgit_test.go b/storage/filesystem/internal/dotgit/dotgit_test.go
index f06f908..6151c8f 100644
--- a/storage/filesystem/internal/dotgit/dotgit_test.go
+++ b/storage/filesystem/internal/dotgit/dotgit_test.go
@@ -12,7 +12,7 @@ import (
 	"gopkg.in/src-d/go-git.v4/plumbing"
 
 	. "gopkg.in/check.v1"
-	"gopkg.in/src-d/go-billy.v2/osfs"
+	"gopkg.in/src-d/go-billy.v3/osfs"
 )
 
 func Test(t *testing.T) { TestingT(t) }
@@ -157,7 +157,7 @@ func (s *SuiteDotGit) TestRemoveRefFromPackedRefs(c *C) {
 	err := dir.RemoveRef(name)
 	c.Assert(err, IsNil)
 
-	b, err := ioutil.ReadFile(filepath.Join(fs.Base(), packedRefsPath))
+	b, err := ioutil.ReadFile(filepath.Join(fs.Root(), packedRefsPath))
 	c.Assert(err, IsNil)
 
 	c.Assert(string(b), Equals, ""+
@@ -170,7 +170,7 @@ func (s *SuiteDotGit) TestRemoveRefNonExistent(c *C) {
 	fs := fixtures.Basic().ByTag(".git").One().DotGit()
 	dir := New(fs)
 
-	packedRefs := filepath.Join(fs.Base(), packedRefsPath)
+	packedRefs := filepath.Join(fs.Root(), packedRefsPath)
 	before, err := ioutil.ReadFile(packedRefs)
 	c.Assert(err, IsNil)
 
@@ -188,7 +188,7 @@ func (s *SuiteDotGit) TestRemoveRefInvalidPackedRefs(c *C) {
 	fs := fixtures.Basic().ByTag(".git").One().DotGit()
 	dir := New(fs)
 
-	packedRefs := filepath.Join(fs.Base(), packedRefsPath)
+	packedRefs := filepath.Join(fs.Root(), packedRefsPath)
 	brokenContent := "BROKEN STUFF REALLY BROKEN"
 
 	err := ioutil.WriteFile(packedRefs, []byte(brokenContent), os.FileMode(0755))
@@ -198,7 +198,7 @@ func (s *SuiteDotGit) TestRemoveRefInvalidPackedRefs(c *C) {
 	err = dir.RemoveRef(name)
 	c.Assert(err, NotNil)
 
-	after, err := ioutil.ReadFile(filepath.Join(fs.Base(), packedRefsPath))
+	after, err := ioutil.ReadFile(filepath.Join(fs.Root(), packedRefsPath))
 	c.Assert(err, IsNil)
 
 	c.Assert(brokenContent, Equals, string(after))
@@ -208,7 +208,7 @@ func (s *SuiteDotGit) TestRemoveRefInvalidPackedRefs2(c *C) {
 	fs := fixtures.Basic().ByTag(".git").One().DotGit()
 	dir := New(fs)
 
-	packedRefs := filepath.Join(fs.Base(), packedRefsPath)
+	packedRefs := filepath.Join(fs.Root(), packedRefsPath)
 	brokenContent := strings.Repeat("a", bufio.MaxScanTokenSize*2)
 
 	err := ioutil.WriteFile(packedRefs, []byte(brokenContent), os.FileMode(0755))
@@ -218,7 +218,7 @@ func (s *SuiteDotGit) TestRemoveRefInvalidPackedRefs2(c *C) {
 	err = dir.RemoveRef(name)
 	c.Assert(err, NotNil)
 
-	after, err := ioutil.ReadFile(filepath.Join(fs.Base(), packedRefsPath))
+	after, err := ioutil.ReadFile(filepath.Join(fs.Root(), packedRefsPath))
 	c.Assert(err, IsNil)
 
 	c.Assert(brokenContent, Equals, string(after))
@@ -243,7 +243,7 @@ func (s *SuiteDotGit) TestConfig(c *C) {
 
 	file, err := dir.Config()
 	c.Assert(err, IsNil)
-	c.Assert(filepath.Base(file.Filename()), Equals, "config")
+	c.Assert(filepath.Base(file.Name()), Equals, "config")
 }
 
 func (s *SuiteDotGit) TestConfigWriteAndConfig(c *C) {
@@ -362,7 +362,7 @@ func (s *SuiteDotGit) TestObjectPack(c *C) {
 
 	pack, err := dir.ObjectPack(f.PackfileHash)
 	c.Assert(err, IsNil)
-	c.Assert(filepath.Ext(pack.Filename()), Equals, ".pack")
+	c.Assert(filepath.Ext(pack.Name()), Equals, ".pack")
 }
 
 func (s *SuiteDotGit) TestObjectPackIdx(c *C) {
@@ -372,7 +372,7 @@ func (s *SuiteDotGit) TestObjectPackIdx(c *C) {
 
 	idx, err := dir.ObjectPackIdx(f.PackfileHash)
 	c.Assert(err, IsNil)
-	c.Assert(filepath.Ext(idx.Filename()), Equals, ".idx")
+	c.Assert(filepath.Ext(idx.Name()), Equals, ".idx")
 }
 
 func (s *SuiteDotGit) TestObjectPackNotFound(c *C) {
@@ -445,7 +445,7 @@ func (s *SuiteDotGit) TestObject(c *C) {
 	file, err := dir.Object(hash)
 	c.Assert(err, IsNil)
 	c.Assert(strings.HasSuffix(
-		file.Filename(), "objects/03/db8e1fbe133a480f2867aac478fd866686d69e"),
+		file.Name(), fs.Join("objects", "03", "db8e1fbe133a480f2867aac478fd866686d69e")),
 		Equals, true,
 	)
 }
@@ -464,6 +464,7 @@ func (s *SuiteDotGit) TestSubmodules(c *C) {
 	fs := fixtures.ByTag("submodule").One().DotGit()
 	dir := New(fs)
 
-	m := dir.Module("basic")
-	c.Assert(strings.HasSuffix(m.Base(), ".git/module/basic"), Equals, true)
+	m, err := dir.Module("basic")
+	c.Assert(err, IsNil)
+	c.Assert(strings.HasSuffix(m.Root(), m.Join(".git", "module", "basic")), Equals, true)
 }
diff --git a/storage/filesystem/internal/dotgit/writers.go b/storage/filesystem/internal/dotgit/writers.go
index 0d2747f..2407c58 100644
--- a/storage/filesystem/internal/dotgit/writers.go
+++ b/storage/filesystem/internal/dotgit/writers.go
@@ -10,7 +10,7 @@ import (
 	"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-billy.v2"
+	"gopkg.in/src-d/go-billy.v3"
 )
 
 // PackWriter is a io.Writer that generates the packfile index simultaneously,
@@ -36,7 +36,7 @@ func newPackWrite(fs billy.Filesystem) (*PackWriter, error) {
 		return nil, err
 	}
 
-	fr, err := fs.Open(fw.Filename())
+	fr, err := fs.Open(fw.Name())
 	if err != nil {
 		return nil, err
 	}
@@ -130,7 +130,7 @@ func (w *PackWriter) Close() error {
 }
 
 func (w *PackWriter) clean() error {
-	return w.fs.Remove(w.fw.Filename())
+	return w.fs.Remove(w.fw.Name())
 }
 
 func (w *PackWriter) save() error {
@@ -148,7 +148,7 @@ func (w *PackWriter) save() error {
 		return err
 	}
 
-	return w.fs.Rename(w.fw.Filename(), fmt.Sprintf("%s.pack", base))
+	return w.fs.Rename(w.fw.Name(), fmt.Sprintf("%s.pack", base))
 }
 
 func (w *PackWriter) encodeIdx(writer io.Writer) error {
@@ -282,5 +282,5 @@ func (w *ObjectWriter) save() error {
 	hash := w.Hash().String()
 	file := w.fs.Join(objectsPath, hash[0:2], hash[2:40])
 
-	return w.fs.Rename(w.f.Filename(), file)
+	return w.fs.Rename(w.f.Name(), file)
 }
diff --git a/storage/filesystem/internal/dotgit/writers_test.go b/storage/filesystem/internal/dotgit/writers_test.go
index e7d7ef9..d2c7b6f 100644
--- a/storage/filesystem/internal/dotgit/writers_test.go
+++ b/storage/filesystem/internal/dotgit/writers_test.go
@@ -11,7 +11,7 @@ import (
 	"github.com/src-d/go-git-fixtures"
 
 	. "gopkg.in/check.v1"
-	"gopkg.in/src-d/go-billy.v2/osfs"
+	"gopkg.in/src-d/go-billy.v3/osfs"
 )
 
 func (s *SuiteDotGit) TestNewObjectPack(c *C) {
diff --git a/storage/filesystem/module.go b/storage/filesystem/module.go
index 2e469d3..6f3de3f 100644
--- a/storage/filesystem/module.go
+++ b/storage/filesystem/module.go
@@ -10,5 +10,10 @@ type ModuleStorage struct {
 }
 
 func (s *ModuleStorage) Module(name string) (storage.Storer, error) {
-	return NewStorage(s.dir.Module(name))
+	fs, err := s.dir.Module(name)
+	if err != nil {
+		return nil, err
+	}
+
+	return NewStorage(fs)
 }
diff --git a/storage/filesystem/object.go b/storage/filesystem/object.go
index 782b99b..dc88108 100644
--- a/storage/filesystem/object.go
+++ b/storage/filesystem/object.go
@@ -12,7 +12,7 @@ import (
 	"gopkg.in/src-d/go-git.v4/storage/filesystem/internal/dotgit"
 	"gopkg.in/src-d/go-git.v4/storage/memory"
 
-	"gopkg.in/src-d/go-billy.v2"
+	"gopkg.in/src-d/go-billy.v3"
 )
 
 type ObjectStorage struct {
diff --git a/storage/filesystem/storage.go b/storage/filesystem/storage.go
index 768238e..2c7c107 100644
--- a/storage/filesystem/storage.go
+++ b/storage/filesystem/storage.go
@@ -4,7 +4,7 @@ package filesystem
 import (
 	"gopkg.in/src-d/go-git.v4/storage/filesystem/internal/dotgit"
 
-	"gopkg.in/src-d/go-billy.v2"
+	"gopkg.in/src-d/go-billy.v3"
 )
 
 // Storage is an implementation of git.Storer that stores data on disk in the
diff --git a/storage/filesystem/storage_test.go b/storage/filesystem/storage_test.go
index 03d2e86..2ced9dd 100644
--- a/storage/filesystem/storage_test.go
+++ b/storage/filesystem/storage_test.go
@@ -7,8 +7,8 @@ import (
 	"gopkg.in/src-d/go-git.v4/storage/test"
 
 	. "gopkg.in/check.v1"
-	"gopkg.in/src-d/go-billy.v2/memfs"
-	"gopkg.in/src-d/go-billy.v2/osfs"
+	"gopkg.in/src-d/go-billy.v3/memfs"
+	"gopkg.in/src-d/go-billy.v3/osfs"
 )
 
 func Test(t *testing.T) { TestingT(t) }
diff --git a/submodule.go b/submodule.go
index fd23b9d..572e6f7 100644
--- a/submodule.go
+++ b/submodule.go
@@ -5,6 +5,7 @@ import (
 	"errors"
 	"fmt"
 
+	billy "gopkg.in/src-d/go-billy.v3"
 	"gopkg.in/src-d/go-git.v4/config"
 	"gopkg.in/src-d/go-git.v4/plumbing"
 	"gopkg.in/src-d/go-git.v4/plumbing/format/index"
@@ -107,8 +108,17 @@ func (s *Submodule) Repository() (*Repository, error) {
 		return nil, err
 	}
 
-	worktree := s.w.fs.Dir(s.c.Path)
+	var exists bool
 	if err == nil {
+		exists = true
+	}
+
+	var worktree billy.Filesystem
+	if worktree, err = s.w.fs.Chroot(s.c.Path); err != nil {
+		return nil, err
+	}
+
+	if exists {
 		return Open(storer, worktree)
 	}
 
diff --git a/submodule_test.go b/submodule_test.go
index fdbe4a8..b398664 100644
--- a/submodule_test.go
+++ b/submodule_test.go
@@ -20,7 +20,7 @@ type SubmoduleSuite struct {
 var _ = Suite(&SubmoduleSuite{})
 
 func (s *SubmoduleSuite) SetUpTest(c *C) {
-	path := fixtures.ByTag("submodule").One().Worktree().Base()
+	path := fixtures.ByTag("submodule").One().Worktree().Root()
 
 	dir, err := ioutil.TempDir("", "submodule")
 	c.Assert(err, IsNil)
@@ -127,7 +127,8 @@ func (s *SubmoduleSuite) TestUpdateWithRecursion(c *C) {
 
 	c.Assert(err, IsNil)
 
-	_, err = s.Worktree.fs.Stat("itself/basic/LICENSE")
+	fs := s.Worktree.fs
+	_, err = fs.Stat(fs.Join("itself", "basic", "LICENSE"))
 	c.Assert(err, IsNil)
 }
 
diff --git a/utils/merkletrie/filesystem/node.go b/utils/merkletrie/filesystem/node.go
index fc8f191..5461bd3 100644
--- a/utils/merkletrie/filesystem/node.go
+++ b/utils/merkletrie/filesystem/node.go
@@ -5,7 +5,7 @@ import (
 	"os"
 	"path/filepath"
 
-	"gopkg.in/src-d/go-billy.v2"
+	"gopkg.in/src-d/go-billy.v3"
 	"gopkg.in/src-d/go-git.v4/plumbing"
 	"gopkg.in/src-d/go-git.v4/plumbing/filemode"
 	"gopkg.in/src-d/go-git.v4/utils/merkletrie/noder"
@@ -106,7 +106,7 @@ func (n *node) calculateChildren() error {
 	return nil
 }
 
-func (n *node) newChildNode(file billy.FileInfo) (*node, error) {
+func (n *node) newChildNode(file os.FileInfo) (*node, error) {
 	path := filepath.Join(n.path, file.Name())
 
 	hash, err := n.calculateHash(path, file)
@@ -131,7 +131,7 @@ func (n *node) newChildNode(file billy.FileInfo) (*node, error) {
 	return node, nil
 }
 
-func (n *node) calculateHash(path string, file billy.FileInfo) ([]byte, error) {
+func (n *node) calculateHash(path string, file os.FileInfo) ([]byte, error) {
 	if file.IsDir() {
 		return make([]byte, 24), nil
 	}
diff --git a/utils/merkletrie/filesystem/node_test.go b/utils/merkletrie/filesystem/node_test.go
index f783c15..a383716 100644
--- a/utils/merkletrie/filesystem/node_test.go
+++ b/utils/merkletrie/filesystem/node_test.go
@@ -7,8 +7,8 @@ import (
 	"testing"
 
 	. "gopkg.in/check.v1"
-	"gopkg.in/src-d/go-billy.v2"
-	"gopkg.in/src-d/go-billy.v2/memfs"
+	"gopkg.in/src-d/go-billy.v3"
+	"gopkg.in/src-d/go-billy.v3/memfs"
 	"gopkg.in/src-d/go-git.v4/plumbing"
 	"gopkg.in/src-d/go-git.v4/utils/merkletrie"
 	"gopkg.in/src-d/go-git.v4/utils/merkletrie/noder"
diff --git a/worktree.go b/worktree.go
index ad6e0f7..aa30b83 100644
--- a/worktree.go
+++ b/worktree.go
@@ -8,6 +8,7 @@ import (
 	"os"
 	"path/filepath"
 
+	"gopkg.in/src-d/go-billy.v3/util"
 	"gopkg.in/src-d/go-git.v4/config"
 	"gopkg.in/src-d/go-git.v4/plumbing"
 	"gopkg.in/src-d/go-git.v4/plumbing/filemode"
@@ -15,7 +16,7 @@ import (
 	"gopkg.in/src-d/go-git.v4/plumbing/object"
 	"gopkg.in/src-d/go-git.v4/utils/merkletrie"
 
-	"gopkg.in/src-d/go-billy.v2"
+	"gopkg.in/src-d/go-billy.v3"
 )
 
 var (
@@ -486,7 +487,7 @@ func (w *Worktree) readGitmodulesFile() (*config.Modules, error) {
 }
 
 func rmFileAndDirIfEmpty(fs billy.Filesystem, name string) error {
-	if err := billy.RemoveAll(fs, name); err != nil {
+	if err := util.RemoveAll(fs, name); err != nil {
 		return err
 	}
 
diff --git a/worktree_commit.go b/worktree_commit.go
index bec75b2..5307b41 100644
--- a/worktree_commit.go
+++ b/worktree_commit.go
@@ -12,7 +12,7 @@ import (
 	"gopkg.in/src-d/go-git.v4/storage"
 	"gopkg.in/src-d/go-git.v4/utils/ioutil"
 
-	"gopkg.in/src-d/go-billy.v2"
+	"gopkg.in/src-d/go-billy.v3"
 )
 
 // Commit stores the current contents of the index in a new commit along with
diff --git a/worktree_commit_test.go b/worktree_commit_test.go
index 7e1b93c..8f3b7b0 100644
--- a/worktree_commit_test.go
+++ b/worktree_commit_test.go
@@ -9,8 +9,8 @@ import (
 	"gopkg.in/src-d/go-git.v4/storage/memory"
 
 	. "gopkg.in/check.v1"
-	"gopkg.in/src-d/go-billy.v2"
-	"gopkg.in/src-d/go-billy.v2/memfs"
+	"gopkg.in/src-d/go-billy.v3/memfs"
+	"gopkg.in/src-d/go-billy.v3/util"
 )
 
 func (s *WorktreeSuite) TestCommitInvalidOptions(c *C) {
@@ -37,7 +37,7 @@ func (s *WorktreeSuite) TestCommitInitial(c *C) {
 	w, err := r.Worktree()
 	c.Assert(err, IsNil)
 
-	billy.WriteFile(fs, "foo", []byte("foo"), 0644)
+	util.WriteFile(fs, "foo", []byte("foo"), 0644)
 
 	_, err = w.Add("foo")
 	c.Assert(err, IsNil)
@@ -61,7 +61,7 @@ func (s *WorktreeSuite) TestCommitParent(c *C) {
 	err := w.Checkout(&CheckoutOptions{})
 	c.Assert(err, IsNil)
 
-	billy.WriteFile(fs, "foo", []byte("foo"), 0644)
+	util.WriteFile(fs, "foo", []byte("foo"), 0644)
 
 	_, err = w.Add("foo")
 	c.Assert(err, IsNil)
@@ -85,8 +85,8 @@ func (s *WorktreeSuite) TestCommitAll(c *C) {
 	err := w.Checkout(&CheckoutOptions{})
 	c.Assert(err, IsNil)
 
-	billy.WriteFile(fs, "LICENSE", []byte("foo"), 0644)
-	billy.WriteFile(fs, "foo", []byte("foo"), 0644)
+	util.WriteFile(fs, "LICENSE", []byte("foo"), 0644)
+	util.WriteFile(fs, "foo", []byte("foo"), 0644)
 
 	hash, err := w.Commit("foo\n", &CommitOptions{
 		All:    true,
diff --git a/worktree_test.go b/worktree_test.go
index 6ca2ed0..4f15005 100644
--- a/worktree_test.go
+++ b/worktree_test.go
@@ -13,9 +13,9 @@ import (
 
 	"github.com/src-d/go-git-fixtures"
 	. "gopkg.in/check.v1"
-	"gopkg.in/src-d/go-billy.v2"
-	"gopkg.in/src-d/go-billy.v2/memfs"
-	"gopkg.in/src-d/go-billy.v2/osfs"
+	"gopkg.in/src-d/go-billy.v3/memfs"
+	"gopkg.in/src-d/go-billy.v3/osfs"
+	"gopkg.in/src-d/go-billy.v3/util"
 )
 
 type WorktreeSuite struct {
@@ -471,7 +471,7 @@ func (s *WorktreeSuite) TestStatusDeleted(c *C) {
 }
 
 func (s *WorktreeSuite) TestSubmodule(c *C) {
-	path := fixtures.ByTag("submodule").One().Worktree().Base()
+	path := fixtures.ByTag("submodule").One().Worktree().Root()
 	r, err := PlainOpen(path)
 	c.Assert(err, IsNil)
 
@@ -485,7 +485,7 @@ func (s *WorktreeSuite) TestSubmodule(c *C) {
 }
 
 func (s *WorktreeSuite) TestSubmodules(c *C) {
-	path := fixtures.ByTag("submodule").One().Worktree().Base()
+	path := fixtures.ByTag("submodule").One().Worktree().Root()
 	r, err := PlainOpen(path)
 	c.Assert(err, IsNil)
 
@@ -512,7 +512,7 @@ func (s *WorktreeSuite) TestAddUntracked(c *C) {
 	c.Assert(err, IsNil)
 	c.Assert(idx.Entries, HasLen, 9)
 
-	err = billy.WriteFile(w.fs, "foo", []byte("FOO"), 0755)
+	err = util.WriteFile(w.fs, "foo", []byte("FOO"), 0755)
 	c.Assert(err, IsNil)
 
 	hash, err := w.Add("foo")
@@ -551,7 +551,7 @@ func (s *WorktreeSuite) TestAddModified(c *C) {
 	c.Assert(err, IsNil)
 	c.Assert(idx.Entries, HasLen, 9)
 
-	err = billy.WriteFile(w.fs, "LICENSE", []byte("FOO"), 0644)
+	err = util.WriteFile(w.fs, "LICENSE", []byte("FOO"), 0644)
 	c.Assert(err, IsNil)
 
 	hash, err := w.Add("LICENSE")