plumbing: format/packfile, fix panic retrieving object hash.

In some cases the original data is not saved before it is cleaned
and forces a panic when it's needed.

The change adds ObjectToPack.CleanOriginal to be used to clean original
object instead of:

    object.Original = nil

Now when the Original data is freed because it's no longer in the pack
window a SetOriginal call is done to make sure that Size, Hash and Size
data is not lost.

Signed-off-by: Javi Fontan <jfontan@gmail.com>

3 files changed, 10 insertions, 4 deletions

diff --git a/plumbing/format/packfile/delta_selector.go b/plumbing/format/packfile/delta_selector.go
index 1d9fb5f..98a91b9 100644
--- a/plumbing/format/packfile/delta_selector.go
+++ b/plumbing/format/packfile/delta_selector.go
@@ -103,7 +103,7 @@ func (dw *deltaSelector) objectsToPack(
 
 		otp := newObjectToPack(o)
 		if _, ok := o.(plumbing.DeltaObject); ok {
-			otp.Original = nil
+			otp.CleanOriginal()
 		}
 
 		objectsToPack = append(objectsToPack, otp)
@@ -231,7 +231,8 @@ func (dw *deltaSelector) walk(
 			delete(indexMap, obj.Hash())
 
 			if obj.IsDelta() {
-				obj.Original = nil
+				obj.SetOriginal(obj.Original)
+				obj.CleanOriginal()
 			}
 		}
 
diff --git a/plumbing/format/packfile/encoder_test.go b/plumbing/format/packfile/encoder_test.go
index 63dfafa..84d03fb 100644
--- a/plumbing/format/packfile/encoder_test.go
+++ b/plumbing/format/packfile/encoder_test.go
@@ -233,10 +233,10 @@ func (s *EncoderSuite) deltaOverDeltaCyclicTest(c *C) {
 	// is nil.
 	po1.SetOriginal(po1.Original)
 	pd2.SetOriginal(pd2.Original)
-	pd2.SetOriginal(nil)
+	pd2.CleanOriginal()
 
 	pd3.SetOriginal(pd3.Original)
-	pd3.SetOriginal(nil)
+	pd3.CleanOriginal()
 
 	pd4.SetOriginal(pd4.Original)
 
diff --git a/plumbing/format/packfile/object_pack.go b/plumbing/format/packfile/object_pack.go
index 877581e..661278d 100644
--- a/plumbing/format/packfile/object_pack.go
+++ b/plumbing/format/packfile/object_pack.go
@@ -90,6 +90,11 @@ func (o *ObjectToPack) SetOriginal(obj plumbing.EncodedObject) {
 	}
 }
 
+// CleanOriginal sets Original to nil
+func (o *ObjectToPack) CleanOriginal() {
+	o.Original = nil
+}
+
 func (o *ObjectToPack) Type() plumbing.ObjectType {
 	if o.Original != nil {
 		return o.Original.Type()