remote: fetch, adds the prune option.

options.go

@@ -166,7 +166,7 @@ const (
 	// AllTags fetch all tags from the remote (i.e., fetch remote tags
 	// refs/tags/* into local tags with the same name)
 	AllTags
-	//NoTags fetch no tags from the remote at all
+	// NoTags fetch no tags from the remote at all
 	NoTags
 )
 
@@ -198,6 +198,9 @@ type FetchOptions struct {
 	CABundle []byte
 	// ProxyOptions provides info required for connecting to a proxy.
 	ProxyOptions transport.ProxyOptions
+	// Prune specify that local refs that match given RefSpecs and that do
+	// not exist remotely will be removed.
+	Prune bool
 }
 
 // Validate validates the fields and sets the default values.

remote.go

@@ -470,6 +470,14 @@ func (r *Remote) fetch(ctx context.Context, o *FetchOptions) (sto storer.Referen
 		}
 	}
 
+	var updatedPrune bool
+	if o.Prune {
+		updatedPrune, err = r.pruneRemotes(o.RefSpecs, localRefs, remoteRefs)
+		if err != nil {
+			return nil, err
+		}
+	}
+
 	updated, err := r.updateLocalReferenceStorage(o.RefSpecs, refs, remoteRefs, specToRefs, o.Tags, o.Force)
 	if err != nil {
 		return nil, err
@@ -482,7 +490,7 @@ func (r *Remote) fetch(ctx context.Context, o *FetchOptions) (sto storer.Referen
 		}
 	}
 
-	if !updated {
+	if !updated && !updatedPrune {
 		return remoteRefs, NoErrAlreadyUpToDate
 	}
 
@@ -574,6 +582,27 @@ func (r *Remote) fetchPack(ctx context.Context, o *FetchOptions, s transport.Upl
 	return err
 }
 
+func (r *Remote) pruneRemotes(specs []config.RefSpec, localRefs []*plumbing.Reference, remoteRefs memory.ReferenceStorage) (bool, error) {
+	var updatedPrune bool
+	for _, spec := range specs {
+		rev := spec.Reverse()
+		for _, ref := range localRefs {
+			if !rev.Match(ref.Name()) {
+				continue
+			}
+			_, err := remoteRefs.Reference(rev.Dst(ref.Name()))
+			if errors.Is(err, plumbing.ErrReferenceNotFound) {
+				updatedPrune = true
+				err := r.s.RemoveReference(ref.Name())
+				if err != nil {
+					return false, err
+				}
+			}
+		}
+	}
+	return updatedPrune, nil
+}
+
 func (r *Remote) addReferencesToUpdate(
 	refspecs []config.RefSpec,
 	localRefs []*plumbing.Reference,

remote_test.go

@@ -1444,6 +1444,120 @@ func (s *RemoteSuite) TestPushRequireRemoteRefs(c *C) {
 	c.Assert(newRef, Not(DeepEquals), oldRef)
 }
 
+func (s *RemoteSuite) TestFetchPrune(c *C) {
+	fs := fixtures.Basic().One().DotGit()
+
+	url, clean := s.TemporalDir()
+	defer clean()
+
+	_, err := PlainClone(url, true, &CloneOptions{
+		URL: fs.Root(),
+	})
+	c.Assert(err, IsNil)
+
+	dir, clean := s.TemporalDir()
+	defer clean()
+
+	r, err := PlainClone(dir, true, &CloneOptions{
+		URL: url,
+	})
+	c.Assert(err, IsNil)
+
+	remote, err := r.Remote(DefaultRemoteName)
+	c.Assert(err, IsNil)
+
+	ref, err := r.Reference(plumbing.ReferenceName("refs/heads/master"), true)
+	c.Assert(err, IsNil)
+
+	err = remote.Push(&PushOptions{RefSpecs: []config.RefSpec{
+		"refs/heads/master:refs/heads/branch",
+	}})
+	c.Assert(err, IsNil)
+
+	dirSave, clean := s.TemporalDir()
+	defer clean()
+
+	rSave, err := PlainClone(dirSave, true, &CloneOptions{
+		URL: url,
+	})
+	c.Assert(err, IsNil)
+
+	AssertReferences(c, rSave, map[string]string{
+		"refs/remotes/origin/branch": ref.Hash().String(),
+	})
+
+	err = remote.Push(&PushOptions{RefSpecs: []config.RefSpec{
+		":refs/heads/branch",
+	}})
+
+	AssertReferences(c, rSave, map[string]string{
+		"refs/remotes/origin/branch": ref.Hash().String(),
+	})
+
+	err = rSave.Fetch(&FetchOptions{Prune: true})
+	c.Assert(err, IsNil)
+
+	_, err = rSave.Reference("refs/remotes/origin/branch", true)
+	c.Assert(err, ErrorMatches, "reference not found")
+}
+
+func (s *RemoteSuite) TestFetchPruneTags(c *C) {
+	fs := fixtures.Basic().One().DotGit()
+
+	url, clean := s.TemporalDir()
+	defer clean()
+
+	_, err := PlainClone(url, true, &CloneOptions{
+		URL: fs.Root(),
+	})
+	c.Assert(err, IsNil)
+
+	dir, clean := s.TemporalDir()
+	defer clean()
+
+	r, err := PlainClone(dir, true, &CloneOptions{
+		URL: url,
+	})
+	c.Assert(err, IsNil)
+
+	remote, err := r.Remote(DefaultRemoteName)
+	c.Assert(err, IsNil)
+
+	ref, err := r.Reference(plumbing.ReferenceName("refs/heads/master"), true)
+	c.Assert(err, IsNil)
+
+	err = remote.Push(&PushOptions{RefSpecs: []config.RefSpec{
+		"refs/heads/master:refs/tags/v1",
+	}})
+	c.Assert(err, IsNil)
+
+	dirSave, clean := s.TemporalDir()
+	defer clean()
+
+	rSave, err := PlainClone(dirSave, true, &CloneOptions{
+		URL: url,
+	})
+	c.Assert(err, IsNil)
+
+	AssertReferences(c, rSave, map[string]string{
+		"refs/tags/v1": ref.Hash().String(),
+	})
+
+	err = remote.Push(&PushOptions{RefSpecs: []config.RefSpec{
+		":refs/tags/v1",
+	}})
+
+	AssertReferences(c, rSave, map[string]string{
+		"refs/tags/v1": ref.Hash().String(),
+	})
+
+	err = rSave.Fetch(&FetchOptions{Prune: true, RefSpecs: []config.RefSpec{"refs/tags/*:refs/tags/*"}})
+	c.Assert(err, IsNil)
+
+	_, err = rSave.Reference("refs/tags/v1", true)
+	c.Assert(err, ErrorMatches, "reference not found")
+}
+
 func (s *RemoteSuite) TestCanPushShasToReference(c *C) {
 	d, err := os.MkdirTemp("", "TestCanPushShasToReference")
 	c.Assert(err, IsNil)