git/githistory: teach UpdateRefs option

git/githistory/rewriter.go

@@ -8,6 +8,7 @@ import (
 	"path/filepath"
 	"sync"
 
+	"github.com/git-lfs/git-lfs/errors"
 	"github.com/git-lfs/git-lfs/filepathfilter"
 	"github.com/git-lfs/git-lfs/git"
 	"github.com/git-lfs/git-lfs/git/githistory/log"
@@ -46,6 +47,11 @@ type RewriteOptions struct {
 	// will be excluded.
 	Exclude []string
 
+	// UpdateRefs specifies whether the Rewriter should move refs from the
+	// original graph onto the migrated one. If true, the refs will be
+	// moved, and a reflog entry will be created.
+	UpdateRefs bool
+
 	// BlobFn specifies a function to rewrite blobs.
 	//
 	// It is called once per unique, unchanged path. That is to say, if
@@ -233,6 +239,26 @@ func (r *Rewriter) Rewrite(opt *RewriteOptions) ([]byte, error) {
 		tip = rewrittenCommit
 	}
 
+	if opt.UpdateRefs {
+		refs, err := r.refsToMigrate()
+		if err != nil {
+			return nil, errors.Wrap(err, "could not find refs to update")
+		}
+
+		root, _ := r.db.Root()
+
+		updater := &refUpdater{
+			CacheFn: r.uncacheCommit,
+			Logger:  r.l,
+			Refs:    refs,
+			Root:    root,
+		}
+
+		if err := updater.UpdateRefs(); err != nil {
+			return nil, errors.Wrap(err, "could not update refs")
+		}
+	}
+
 	r.l.Close()
 
 	return tip, err

git/githistory/rewriter_test.go

@@ -299,6 +299,37 @@ func TestHistoryRewriterUseOriginalParentsForPartialMigration(t *testing.T) {
 	AssertCommitParent(t, db, hex.EncodeToString(tip), expectedParent)
 }
 
+func TestHistoryRewriterUpdatesRefs(t *testing.T) {
+	db := DatabaseFromFixture(t, "linear-history.git")
+	r := NewRewriter(db)
+
+	tip, err := r.Rewrite(&RewriteOptions{
+		Include: []string{"refs/heads/master"},
+
+		UpdateRefs: true,
+
+		BlobFn: func(path string, b *odb.Blob) (*odb.Blob, error) {
+			suffix := strings.NewReader("_suffix")
+
+			return &odb.Blob{
+				Contents: io.MultiReader(b.Contents, suffix),
+				Size:     b.Size + int64(suffix.Len()),
+			}, nil
+		},
+	})
+
+	assert.Nil(t, err)
+
+	c1 := hex.EncodeToString(tip)
+	c2 := "66561fe3ae68651658e18e48053dcfe66a2e9da1"
+	c3 := "8268d8486c48024a871fa42fc487dbeabd6e3d86"
+
+	AssertRef(t, db, "refs/heads/master", tip)
+
+	AssertCommitParent(t, db, c1, c2)
+	AssertCommitParent(t, db, c2, c3)
+}
+
 func root(path string) string {
 	if !strings.HasPrefix(path, string(os.PathSeparator)) {
 		path = string(os.PathSeparator) + path