5 files changed, 30 insertions, 7 deletions
diff --git a/plumbing/format/packfile/encoder.go b/plumbing/format/packfile/encoder.go
index a8a7e96..c9d19b3 100644
--- a/plumbing/format/packfile/encoder.go
+++ b/plumbing/format/packfile/encoder.go
@@ -2,7 +2,6 @@ package packfile
 
 import (
 	"compress/zlib"
-	"crypto"
 	"fmt"
 	"io"
 
@@ -29,7 +28,7 @@ type Encoder struct {
 // OFSDeltaObject. To use Reference deltas, set useRefDeltas to true.
 func NewEncoder(w io.Writer, s storer.EncodedObjectStorer, useRefDeltas bool) *Encoder {
 	h := plumbing.Hasher{
-		Hash: hash.New(crypto.SHA1),
+		Hash: hash.New(hash.CryptoType),
 	}
 	mw := io.MultiWriter(w, h)
 	ow := newOffsetWriter(mw)
diff --git a/plumbing/format/packfile/encoder_test.go b/plumbing/format/packfile/encoder_test.go
index c9d49c3..902d8cc 100644
--- a/plumbing/format/packfile/encoder_test.go
+++ b/plumbing/format/packfile/encoder_test.go
@@ -7,6 +7,7 @@ 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/hash"
 	"github.com/go-git/go-git/v5/storage/memory"
 
 	"github.com/go-git/go-billy/v5/memfs"
@@ -30,10 +31,10 @@ func (s *EncoderSuite) SetUpTest(c *C) {
 }
 
 func (s *EncoderSuite) TestCorrectPackHeader(c *C) {
-	hash, err := s.enc.Encode([]plumbing.Hash{}, 10)
+	h, err := s.enc.Encode([]plumbing.Hash{}, 10)
 	c.Assert(err, IsNil)
 
-	hb := [20]byte(hash)
+	hb := [hash.Size]byte(h)
 
 	// PACK + VERSION + OBJECTS + HASH
 	expectedResult := []byte{'P', 'A', 'C', 'K', 0, 0, 0, 2, 0, 0, 0, 0}
@@ -51,7 +52,7 @@ func (s *EncoderSuite) TestCorrectPackWithOneEmptyObject(c *C) {
 	_, err := s.store.SetEncodedObject(o)
 	c.Assert(err, IsNil)
 
-	hash, err := s.enc.Encode([]plumbing.Hash{o.Hash()}, 10)
+	h, err := s.enc.Encode([]plumbing.Hash{o.Hash()}, 10)
 	c.Assert(err, IsNil)
 
 	// PACK + VERSION(2) + OBJECT NUMBER(1)
@@ -64,7 +65,7 @@ func (s *EncoderSuite) TestCorrectPackWithOneEmptyObject(c *C) {
 		[]byte{120, 156, 1, 0, 0, 255, 255, 0, 0, 0, 1}...)
 
 	// + HASH
-	hb := [20]byte(hash)
+	hb := [hash.Size]byte(h)
 	expectedResult = append(expectedResult, hb[:]...)
 
 	result := s.buf.Bytes()
diff --git a/plumbing/format/packfile/parser.go b/plumbing/format/packfile/parser.go
index 522c146..6012b04 100644
--- a/plumbing/format/packfile/parser.go
+++ b/plumbing/format/packfile/parser.go
@@ -237,6 +237,15 @@ func (p *Parser) indexObjects() error {
 				return err
 			}
 
+			// Move children of placeholder parent into actual parent, in case this
+			// was a non-external delta reference.
+			if placeholder, ok := p.oiByHash[sha1]; ok {
+				ota.Children = placeholder.Children
+				for _, c := range ota.Children {
+					c.Parent = ota
+				}
+			}
+
 			ota.SHA1 = sha1
 			p.oiByHash[ota.SHA1] = ota
 		}
diff --git a/plumbing/format/packfile/parser_test.go b/plumbing/format/packfile/parser_test.go
index 651d05f..b8d080f 100644
--- a/plumbing/format/packfile/parser_test.go
+++ b/plumbing/format/packfile/parser_test.go
@@ -147,6 +147,19 @@ func (s *ParserSuite) TestResolveExternalRefsInThinPack(c *C) {
 	c.Assert(err, IsNil)
 }
 
+func (s *ParserSuite) TestResolveExternalRefs(c *C) {
+	extRefsThinPack := fixtures.ByTag("delta-before-base").One()
+
+	scanner := packfile.NewScanner(extRefsThinPack.Packfile())
+
+	obs := new(testObserver)
+	parser, err := packfile.NewParser(scanner, obs)
+	c.Assert(err, IsNil)
+
+	_, err = parser.Parse()
+	c.Assert(err, IsNil)
+}
+
 type observerObject struct {
 	hash   string
 	otype  plumbing.ObjectType
diff --git a/plumbing/format/packfile/scanner_test.go b/plumbing/format/packfile/scanner_test.go
index 892a27c..9dcc359 100644
--- a/plumbing/format/packfile/scanner_test.go
+++ b/plumbing/format/packfile/scanner_test.go
@@ -6,6 +6,7 @@ import (
 
 	fixtures "github.com/go-git/go-git-fixtures/v4"
 	"github.com/go-git/go-git/v5/plumbing"
+	"github.com/go-git/go-git/v5/plumbing/hash"
 
 	. "gopkg.in/check.v1"
 )
@@ -71,7 +72,7 @@ func (s *ScannerSuite) testNextObjectHeader(c *C, tag string,
 
 	n, err := p.Checksum()
 	c.Assert(err, IsNil)
-	c.Assert(n, HasLen, 20)
+	c.Assert(n, HasLen, hash.Size)
 }
 
 func (s *ScannerSuite) TestNextObjectHeaderWithOutReadObject(c *C) {