Remove unused variables/types/functions

[staticcheck](https://staticcheck.io/) reported a number of unused
fields, functions, types, and variables across the code.

Where possible, use them (assert unchecked errors in tests, for example)
and otherwise remove them.

20 files changed, 12 insertions, 85 deletions

diff --git a/common_test.go b/common_test.go
index b47f5bb..c0c4009 100644
--- a/common_test.go
+++ b/common_test.go
@@ -7,7 +7,6 @@ import (
 	"github.com/go-git/go-git/v5/plumbing"
 	"github.com/go-git/go-git/v5/plumbing/cache"
 	"github.com/go-git/go-git/v5/plumbing/format/packfile"
-	"github.com/go-git/go-git/v5/plumbing/transport"
 	"github.com/go-git/go-git/v5/storage/filesystem"
 	"github.com/go-git/go-git/v5/storage/memory"
 
@@ -25,8 +24,7 @@ type BaseSuite struct {
 	fixtures.Suite
 	Repository *Repository
 
-	backupProtocol transport.Transport
-	cache          map[string]*Repository
+	cache map[string]*Repository
 }
 
 func (s *BaseSuite) SetUpSuite(c *C) {
diff --git a/config/config_test.go b/config/config_test.go
index 6f0242d..5a51bb3 100644
--- a/config/config_test.go
+++ b/config/config_test.go
@@ -361,6 +361,7 @@ func (s *ConfigSuite) TestRemoveUrlOptions(c *C) {
 	cfg.Remotes["alt"].URLs = []string{}
 
 	buf, err = cfg.Marshal()
+	c.Assert(err, IsNil)
 	if strings.Contains(string(buf), "url") {
 		c.Fatal("conifg should not contain any url sections")
 	}
diff --git a/plumbing/format/packfile/fsobject.go b/plumbing/format/packfile/fsobject.go
index a395d17..238339d 100644
--- a/plumbing/format/packfile/fsobject.go
+++ b/plumbing/format/packfile/fsobject.go
@@ -13,7 +13,6 @@ import (
 // FSObject is an object from the packfile on the filesystem.
 type FSObject struct {
 	hash                 plumbing.Hash
-	h                    *ObjectHeader
 	offset               int64
 	size                 int64
 	typ                  plumbing.ObjectType
@@ -118,17 +117,3 @@ func (o *FSObject) Type() plumbing.ObjectType {
 func (o *FSObject) Writer() (io.WriteCloser, error) {
 	return nil, nil
 }
-
-type objectReader struct {
-	io.ReadCloser
-	f billy.File
-}
-
-func (r *objectReader) Close() error {
-	if err := r.ReadCloser.Close(); err != nil {
-		_ = r.f.Close()
-		return err
-	}
-
-	return r.f.Close()
-}
diff --git a/plumbing/format/packfile/packfile_test.go b/plumbing/format/packfile/packfile_test.go
index 6af8817..2eb099d 100644
--- a/plumbing/format/packfile/packfile_test.go
+++ b/plumbing/format/packfile/packfile_test.go
@@ -8,7 +8,6 @@ import (
 	"github.com/go-git/go-git/v5/plumbing"
 	"github.com/go-git/go-git/v5/plumbing/format/idxfile"
 	"github.com/go-git/go-git/v5/plumbing/format/packfile"
-	"github.com/go-git/go-git/v5/plumbing/storer"
 	. "gopkg.in/check.v1"
 )
 
@@ -236,22 +235,6 @@ var expectedHashes = []string{
 	"7e59600739c96546163833214c36459e324bad0a",
 }
 
-func assertObjects(c *C, s storer.EncodedObjectStorer, expects []string) {
-	i, err := s.IterEncodedObjects(plumbing.AnyObject)
-	c.Assert(err, IsNil)
-
-	var count int
-	err = i.ForEach(func(plumbing.EncodedObject) error { count++; return nil })
-	c.Assert(err, IsNil)
-	c.Assert(count, Equals, len(expects))
-
-	for _, exp := range expects {
-		obt, err := s.EncodedObject(plumbing.AnyObject, plumbing.NewHash(exp))
-		c.Assert(err, IsNil)
-		c.Assert(obt.Hash().String(), Equals, exp)
-	}
-}
-
 func getIndexFromIdxFile(r io.Reader) idxfile.Index {
 	idx := idxfile.NewMemoryIndex()
 	if err := idxfile.NewDecoder(r).Decode(idx); err != nil {
diff --git a/plumbing/format/packfile/parser.go b/plumbing/format/packfile/parser.go
index 4b5a570..ee5c289 100644
--- a/plumbing/format/packfile/parser.go
+++ b/plumbing/format/packfile/parser.go
@@ -46,7 +46,6 @@ type Parser struct {
 	oi         []*objectInfo
 	oiByHash   map[plumbing.Hash]*objectInfo
 	oiByOffset map[int64]*objectInfo
-	hashOffset map[plumbing.Hash]int64
 	checksum   plumbing.Hash
 
 	cache *cache.BufferLRU
diff --git a/plumbing/object/patch.go b/plumbing/object/patch.go
index 56b62c1..06bc35b 100644
--- a/plumbing/object/patch.go
+++ b/plumbing/object/patch.go
@@ -96,10 +96,6 @@ func filePatchWithContext(ctx context.Context, c *Change) (fdiff.FilePatch, erro
 
 }
 
-func filePatch(c *Change) (fdiff.FilePatch, error) {
-	return filePatchWithContext(context.Background(), c)
-}
-
 func fileContent(f *File) (content string, isBinary bool, err error) {
 	if f == nil {
 		return
diff --git a/plumbing/protocol/packp/common.go b/plumbing/protocol/packp/common.go
index ab07ac8..fef50a4 100644
--- a/plumbing/protocol/packp/common.go
+++ b/plumbing/protocol/packp/common.go
@@ -19,7 +19,6 @@ var (
 	// common
 	sp  = []byte(" ")
 	eol = []byte("\n")
-	eq  = []byte{'='}
 
 	// advertised-refs
 	null       = []byte("\x00")
diff --git a/plumbing/protocol/packp/updreq_encode.go b/plumbing/protocol/packp/updreq_encode.go
index 08a819e..1205cfa 100644
--- a/plumbing/protocol/packp/updreq_encode.go
+++ b/plumbing/protocol/packp/updreq_encode.go
@@ -9,10 +9,6 @@ import (
 	"github.com/go-git/go-git/v5/plumbing/protocol/packp/capability"
 )
 
-var (
-	zeroHashString = plumbing.ZeroHash.String()
-)
-
 // Encode writes the ReferenceUpdateRequest encoding to the stream.
 func (req *ReferenceUpdateRequest) Encode(w io.Writer) error {
 	if err := req.validate(); err != nil {
diff --git a/plumbing/protocol/packp/uppackresp.go b/plumbing/protocol/packp/uppackresp.go
index a9a7192..26ae61e 100644
--- a/plumbing/protocol/packp/uppackresp.go
+++ b/plumbing/protocol/packp/uppackresp.go
@@ -24,7 +24,6 @@ type UploadPackResponse struct {
 	r          io.ReadCloser
 	isShallow  bool
 	isMultiACK bool
-	isOk       bool
 }
 
 // NewUploadPackResponse create a new UploadPackResponse instance, the request
diff --git a/plumbing/revlist/revlist_test.go b/plumbing/revlist/revlist_test.go
index a1ee504..9f2f93b 100644
--- a/plumbing/revlist/revlist_test.go
+++ b/plumbing/revlist/revlist_test.go
@@ -55,12 +55,6 @@ func (s *RevListSuite) SetUpTest(c *C) {
 	s.Storer = sto
 }
 
-func (s *RevListSuite) commit(c *C, h plumbing.Hash) *object.Commit {
-	commit, err := object.GetCommit(s.Storer, h)
-	c.Assert(err, IsNil)
-	return commit
-}
-
 func (s *RevListSuite) TestRevListObjects_Submodules(c *C) {
 	submodules := map[string]bool{
 		"6ecf0ef2c2dffb796033e5a02219af86ec6584e5": true,
diff --git a/plumbing/transport/client/client_test.go b/plumbing/transport/client/client_test.go
index 9ebe113..92db525 100644
--- a/plumbing/transport/client/client_test.go
+++ b/plumbing/transport/client/client_test.go
@@ -1,7 +1,6 @@
 package client
 
 import (
-	"fmt"
 	"net/http"
 	"testing"
 
@@ -68,7 +67,3 @@ func (*dummyClient) NewReceivePackSession(*transport.Endpoint, transport.AuthMet
 	transport.ReceivePackSession, error) {
 	return nil, nil
 }
-
-func typeAsString(v interface{}) string {
-	return fmt.Sprintf("%T", v)
-}
diff --git a/plumbing/transport/internal/common/common.go b/plumbing/transport/internal/common/common.go
index fdb148f..d0e9a29 100644
--- a/plumbing/transport/internal/common/common.go
+++ b/plumbing/transport/internal/common/common.go
@@ -428,11 +428,6 @@ func isRepoNotFoundError(s string) bool {
 	return false
 }
 
-var (
-	nak = []byte("NAK")
-	eol = []byte("\n")
-)
-
 // uploadPack implements the git-upload-pack protocol.
 func uploadPack(w io.WriteCloser, r io.Reader, req *packp.UploadPackRequest) error {
 	// TODO support multi_ack mode
diff --git a/plumbing/transport/ssh/common_test.go b/plumbing/transport/ssh/common_test.go
index e04a9c5..6d634d5 100644
--- a/plumbing/transport/ssh/common_test.go
+++ b/plumbing/transport/ssh/common_test.go
@@ -7,7 +7,6 @@ import (
 
 	"github.com/kevinburke/ssh_config"
 	"golang.org/x/crypto/ssh"
-	stdssh "golang.org/x/crypto/ssh"
 	. "gopkg.in/check.v1"
 )
 
@@ -99,7 +98,7 @@ func (s *SuiteCommon) TestIssue70(c *C) {
 	uploadPack.SetUpSuite(c)
 
 	config := &ssh.ClientConfig{
-		HostKeyCallback: stdssh.InsecureIgnoreHostKey(),
+		HostKeyCallback: ssh.InsecureIgnoreHostKey(),
 	}
 	r := &runner{
 		config: config,
diff --git a/remote.go b/remote.go
index 426bde9..d54693e 100644
--- a/remote.go
+++ b/remote.go
@@ -256,7 +256,7 @@ func (r *Remote) addReachableTags(localRefs []*plumbing.Reference, remoteRefs st
 		return err
 	}
 
-	for tag, _ := range tags {
+	for tag := range tags {
 		tagObject, err := object.GetObject(r.s, tag.Hash())
 		var tagCommit *object.Commit
 		if err != nil {
diff --git a/remote_test.go b/remote_test.go
index df07c08..e41d802 100644
--- a/remote_test.go
+++ b/remote_test.go
@@ -875,7 +875,7 @@ func (s *RemoteSuite) TestPushPrune(c *C) {
 		"refs/remotes/origin/master": ref.Hash().String(),
 	})
 
-	ref, err = server.Reference(plumbing.ReferenceName("refs/tags/v1.0.0"), true)
+	_, err = server.Reference(plumbing.ReferenceName("refs/tags/v1.0.0"), true)
 	c.Assert(err, Equals, plumbing.ErrReferenceNotFound)
 }
 
diff --git a/storage/filesystem/dotgit/dotgit_test.go b/storage/filesystem/dotgit/dotgit_test.go
index 4c2ae94..1db1a04 100644
--- a/storage/filesystem/dotgit/dotgit_test.go
+++ b/storage/filesystem/dotgit/dotgit_test.go
@@ -653,7 +653,7 @@ func (s *SuiteDotGit) TestObject(c *C) {
 	fs.MkdirAll(incomingDirPath, os.FileMode(0755))
 	fs.Create(incomingFilePath)
 
-	file, err = dir.Object(plumbing.NewHash(incomingHash))
+	_, err = dir.Object(plumbing.NewHash(incomingHash))
 	c.Assert(err, IsNil)
 }
 
diff --git a/storage/filesystem/object_test.go b/storage/filesystem/object_test.go
index 59b40d3..9c5e31f 100644
--- a/storage/filesystem/object_test.go
+++ b/storage/filesystem/object_test.go
@@ -386,7 +386,7 @@ func (s *FsSuite) TestGetFromObjectFileSharedCache(c *C) {
 	c.Assert(err, IsNil)
 	c.Assert(obj.Hash(), Equals, expected)
 
-	obj, err = o2.EncodedObject(plumbing.CommitObject, expected)
+	_, err = o2.EncodedObject(plumbing.CommitObject, expected)
 	c.Assert(err, Equals, plumbing.ErrObjectNotFound)
 }
 
diff --git a/utils/merkletrie/noder/noder_test.go b/utils/merkletrie/noder/noder_test.go
index 5e014fe..110e465 100644
--- a/utils/merkletrie/noder/noder_test.go
+++ b/utils/merkletrie/noder/noder_test.go
@@ -57,20 +57,6 @@ func childrenFixture() []Noder {
 	return []Noder{c1, c2}
 }
 
-// Returns the same as nodersFixture but sorted by name, this is: "1",
-// "2" and then "3".
-func sortedNodersFixture() []Noder {
-	n1 := &noderMock{
-		name:     "1",
-		hash:     []byte{0x00, 0x01, 0x02},
-		isDir:    true,
-		children: childrenFixture(),
-	}
-	n2 := &noderMock{name: "2"}
-	n3 := &noderMock{name: "3"}
-	return []Noder{n1, n2, n3} // the same as nodersFixture but sorted by name
-}
-
 // returns nodersFixture as the path of "1".
 func pathFixture() Path {
 	return Path(nodersFixture())
diff --git a/worktree_commit_test.go b/worktree_commit_test.go
index 65d4b69..097c6e5 100644
--- a/worktree_commit_test.go
+++ b/worktree_commit_test.go
@@ -212,10 +212,10 @@ func (s *WorktreeSuite) TestCommitTreeSort(c *C) {
 	defer clean()
 
 	st := filesystem.NewStorage(fs, cache.NewObjectLRUDefault())
-	r, err := Init(st, nil)
+	_, err := Init(st, nil)
 	c.Assert(err, IsNil)
 
-	r, _ = Clone(memory.NewStorage(), memfs.New(), &CloneOptions{
+	r, _ := Clone(memory.NewStorage(), memfs.New(), &CloneOptions{
 		URL: fs.Root(),
 	})
 
@@ -296,6 +296,7 @@ func (s *WorktreeSuite) TestJustStoreObjectsNotAlreadyStored(c *C) {
 		All:    true,
 		Author: defaultSignature(),
 	})
+	c.Assert(err, IsNil)
 	c.Assert(hash, Equals, plumbing.NewHash("97c0c5177e6ac57d10e8ea0017f2d39b91e2b364"))
 
 	// Step 3: Check
diff --git a/worktree_test.go b/worktree_test.go
index 79cbefd..97dcc30 100644
--- a/worktree_test.go
+++ b/worktree_test.go
@@ -183,7 +183,7 @@ func (s *WorktreeSuite) TestPullInSingleBranch(c *C) {
 	c.Assert(err, IsNil)
 	c.Assert(branch.Hash().String(), Equals, "6ecf0ef2c2dffb796033e5a02219af86ec6584e5")
 
-	branch, err = r.Reference("refs/remotes/foo/branch", false)
+	_, err = r.Reference("refs/remotes/foo/branch", false)
 	c.Assert(err, NotNil)
 
 	storage := r.Storer.(*memory.Storage)
@@ -555,6 +555,7 @@ func (s *WorktreeSuite) TestCheckoutRelativePathSubmoduleInitialized(c *C) {
 
 	// test submodule path
 	modules, err := w.readGitmodulesFile()
+	c.Assert(err, IsNil)
 
 	c.Assert(modules.Submodules["basic"].URL, Equals, "../basic.git")
 	c.Assert(modules.Submodules["itself"].URL, Equals, "../submodule.git")