git: add mirror clone option

config/config.go

@@ -264,6 +264,7 @@ const (
 	defaultBranchKey           = "defaultBranch"
 	repositoryFormatVersionKey = "repositoryformatversion"
 	objectFormat               = "objectformat"
+	mirrorKey                  = "mirror"
 
 	// DefaultPackWindow holds the number of previous objects used to
 	// generate deltas. The value 10 is the same used by git command.
@@ -578,6 +579,8 @@ type RemoteConfig struct {
 	// URLs the URLs of a remote repository. It must be non-empty. Fetch will
 	// always use the first URL, while push will use all of them.
 	URLs []string
+	// Mirror indicates that the repository is a mirror of remote.
+	Mirror bool
 
 	// insteadOfRulesApplied have urls been modified
 	insteadOfRulesApplied bool
@@ -631,6 +634,7 @@ func (c *RemoteConfig) unmarshal(s *format.Subsection) error {
 	c.Name = c.raw.Name
 	c.URLs = append([]string(nil), c.raw.Options.GetAll(urlKey)...)
 	c.Fetch = fetch
+	c.Mirror = c.raw.Options.Get(mirrorKey) == "true"
 
 	return nil
 }
@@ -663,6 +667,10 @@ func (c *RemoteConfig) marshal() *format.Subsection {
 		c.raw.SetOption(fetchKey, values...)
 	}
 
+	if c.Mirror {
+		c.raw.SetOption(mirrorKey, strconv.FormatBool(c.Mirror))
+	}
+
 	return c.raw
 }
 

options.go

@@ -46,6 +46,14 @@ type CloneOptions struct {
 	ReferenceName plumbing.ReferenceName
 	// Fetch only ReferenceName if true.
 	SingleBranch bool
+	// Mirror clones the repository as a mirror.
+	//
+	// Compared to a bare clone, mirror not only maps local branches of the
+	// source to local branches of the target, it maps all refs (including
+	// remote-tracking branches, notes etc.) and sets up a refspec configuration
+	// such that all these refs are overwritten by a git remote update in the
+	// target repository.
+	Mirror bool
 	// No checkout of HEAD after clone if true.
 	NoCheckout bool
 	// Limit fetching to the specified number of commits.

repository.go

@@ -444,6 +444,9 @@ func PlainCloneContext(ctx context.Context, path string, isBare bool, o *CloneOp
 		return nil, err
 	}
 
+	if o.Mirror {
+		isBare = true
+	}
 	r, err := PlainInit(path, isBare)
 	if err != nil {
 		return nil, err
@@ -851,9 +854,10 @@ func (r *Repository) clone(ctx context.Context, o *CloneOptions) error {
 	}
 
 	c := &config.RemoteConfig{
-		Name:  o.RemoteName,
-		URLs:  []string{o.URL},
-		Fetch: r.cloneRefSpec(o),
+		Name:   o.RemoteName,
+		URLs:   []string{o.URL},
+		Fetch:  r.cloneRefSpec(o),
+		Mirror: o.Mirror,
 	}
 
 	if _, err := r.CreateRemote(c); err != nil {
@@ -906,7 +910,7 @@ func (r *Repository) clone(ctx context.Context, o *CloneOptions) error {
 		return err
 	}
 
-	if ref.Name().IsBranch() {
+	if !o.Mirror && ref.Name().IsBranch() {
 		branchRef := ref.Name()
 		branchName := strings.Split(string(branchRef), "refs/heads/")[1]
 
@@ -937,6 +941,8 @@ const (
 
 func (r *Repository) cloneRefSpec(o *CloneOptions) []config.RefSpec {
 	switch {
+	case o.Mirror:
+		return []config.RefSpec{"+refs/*:refs/*"}
 	case o.ReferenceName.IsTag():
 		return []config.RefSpec{
 			config.RefSpec(fmt.Sprintf(refspecTag, o.ReferenceName.Short())),

repository_test.go

@@ -189,6 +189,35 @@ func (s *RepositorySuite) TestCloneContext(c *C) {
 	c.Assert(err, Equals, context.Canceled)
 }
 
+func (s *RepositorySuite) TestCloneMirror(c *C) {
+	r, err := Clone(memory.NewStorage(), nil, &CloneOptions{
+		URL:    fixtures.Basic().One().URL,
+		Mirror: true,
+	})
+
+	c.Assert(err, IsNil)
+
+	refs, err := r.References()
+	var count int
+	refs.ForEach(func(r *plumbing.Reference) error { c.Log(r); count++; return nil })
+	c.Assert(err, IsNil)
+	// 6 refs total from github.com/git-fixtures/basic.git:
+	//  - HEAD
+	//  - refs/heads/master
+	//  - refs/heads/branch
+	//  - refs/pull/1/head
+	//  - refs/pull/2/head
+	//  - refs/pull/2/merge
+	c.Assert(count, Equals, 6)
+
+	cfg, err := r.Config()
+	c.Assert(err, IsNil)
+
+	c.Assert(cfg.Core.IsBare, Equals, true)
+	c.Assert(cfg.Remotes[DefaultRemoteName].Validate(), IsNil)
+	c.Assert(cfg.Remotes[DefaultRemoteName].Mirror, Equals, true)
+}
+
 func (s *RepositorySuite) TestCloneWithTags(c *C) {
 	url := s.GetLocalRepositoryURL(
 		fixtures.ByURL("https://github.com/git-fixtures/tags.git").One(),