pumbling: packfile, resolve external reference delta

fix: resolve external reference delta

.gitignore

@@ -2,3 +2,4 @@ coverage.out
 *~
 coverage.txt
 profile.out
+.tmp/

go.mod

@@ -10,7 +10,7 @@ require (
 	github.com/gliderlabs/ssh v0.2.2
 	github.com/go-git/gcfg v1.5.0
 	github.com/go-git/go-billy/v5 v5.3.1
-	github.com/go-git/go-git-fixtures/v4 v4.2.1
+	github.com/go-git/go-git-fixtures/v4 v4.3.1
 	github.com/google/go-cmp v0.3.0
 	github.com/imdario/mergo v0.3.12
 	github.com/jbenet/go-context v0.0.0-20150711004518-d14ea06fba99

go.sum

@@ -20,11 +20,12 @@ github.com/gliderlabs/ssh v0.2.2 h1:6zsha5zo/TWhRhwqCD3+EarCAgZ2yN28ipRnGPnwkI0=
 github.com/gliderlabs/ssh v0.2.2/go.mod h1:U7qILu1NlMHj9FlMhZLlkCdDnU1DBEAqr0aevW3Awn0=
 github.com/go-git/gcfg v1.5.0 h1:Q5ViNfGF8zFgyJWPqYwA7qGFoMTEiBmdlkcfRmpIMa4=
 github.com/go-git/gcfg v1.5.0/go.mod h1:5m20vg6GwYabIxaOonVkTdrILxQMpEShl1xiMF4ua+E=
-github.com/go-git/go-billy/v5 v5.2.0/go.mod h1:pmpqyWchKfYfrkb/UVH4otLvyi/5gJlGI4Hb3ZqZ3W0=
 github.com/go-git/go-billy/v5 v5.3.1 h1:CPiOUAzKtMRvolEKw+bG1PLRpT7D3LIs3/3ey4Aiu34=
 github.com/go-git/go-billy/v5 v5.3.1/go.mod h1:pmpqyWchKfYfrkb/UVH4otLvyi/5gJlGI4Hb3ZqZ3W0=
-github.com/go-git/go-git-fixtures/v4 v4.2.1 h1:n9gGL1Ct/yIw+nfsfr8s4+sbhT+Ncu2SubfXjIWgci8=
-github.com/go-git/go-git-fixtures/v4 v4.2.1/go.mod h1:K8zd3kDUAykwTdDCr+I0per6Y6vMiRR/nnVTBtavnB0=
+github.com/go-git/go-git-fixtures/v4 v4.3.0 h1:OAiwhtOsTVVUvVSLzwSO9PCCo/KPxGfn5aC3BV6d6TY=
+github.com/go-git/go-git-fixtures/v4 v4.3.0/go.mod h1:8LHG1a3SRW71ettAD/jW13h8c6AqjVSeL11RAdgaqpo=
+github.com/go-git/go-git-fixtures/v4 v4.3.1 h1:y5z6dd3qi8Hl+stezc8p3JxDkoTRqMAlKnXHuzrfjTQ=
+github.com/go-git/go-git-fixtures/v4 v4.3.1/go.mod h1:8LHG1a3SRW71ettAD/jW13h8c6AqjVSeL11RAdgaqpo=
 github.com/google/go-cmp v0.3.0 h1:crn/baboCvb5fXaQ0IJ1SGTsTVrWpDsCWC8EGETZijY=
 github.com/google/go-cmp v0.3.0/go.mod h1:8QqcDgzrUqlUb/G2PQTWiueGozuR1884gddMywk6iLU=
 github.com/imdario/mergo v0.3.12 h1:b6R2BslTbIEToALKP7LxUvijTsNI9TAe80pLWN2g/HU=

plumbing/format/packfile/parser.go

@@ -286,6 +286,7 @@ func (p *Parser) resolveDeltas() error {
 				if err := p.resolveObject(stdioutil.Discard, child, content); err != nil {
 					return err
 				}
+				p.resolveExternalRef(child)
 			}
 
 			// Remove the delta from the cache.
@@ -298,6 +299,16 @@ func (p *Parser) resolveDeltas() error {
 	return nil
 }
 
+func (p *Parser) resolveExternalRef(o *objectInfo) {
+	if ref, ok := p.oiByHash[o.SHA1]; ok && ref.ExternalRef {
+		p.oiByHash[o.SHA1] = o
+		o.Children = ref.Children
+		for _, c := range o.Children {
+			c.Parent = o
+		}
+	}
+}
+
 func (p *Parser) get(o *objectInfo, buf *bytes.Buffer) (err error) {
 	if !o.ExternalRef { // skip cache check for placeholder parents
 		b, ok := p.cache.Get(o.Offset)

plumbing/format/packfile/parser_test.go

@@ -132,6 +132,19 @@ func (s *ParserSuite) TestThinPack(c *C) {
 
 }
 
+func (s *ParserSuite) TestResolveExternalRefsInThinPack(c *C) {
+	extRefsThinPack := fixtures.ByTag("codecommit").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