plumbing: resolve non-external delta references

In a self-contained pack file delta references might point to base
objects stored later in the file.
In this case we need to replace placeholders for external refs with the
actual base object and update the children references.

Fixes: #484

Co-authored-by: Markus Wolf <mail@markus-wolf.de>

2 files changed, 22 insertions, 0 deletions

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