plumbing/object: move difftree to object package

- To avoid ciclic dependency errors, we move all the difftree files to object package.
- Added Diff method to Tree object.

1 files changed, 62 insertions, 0 deletions

diff --git a/plumbing/object/difftree.go b/plumbing/object/difftree.go
new file mode 100644
index 0000000..e6e0cb0
--- /dev/null
+++ b/plumbing/object/difftree.go
@@ -0,0 +1,62 @@
+package object
+
+import (
+	"bytes"
+	"os"
+
+	"srcd.works/go-git.v4/utils/merkletrie"
+	"srcd.works/go-git.v4/utils/merkletrie/noder"
+)
+
+// DiffTree compares the content and mode of the blobs found via two
+// tree objects.
+func DiffTree(a, b *Tree) (Changes, error) {
+	from := newTreeNoder(a)
+	to := newTreeNoder(b)
+
+	merkletrieChanges, err := merkletrie.DiffTree(from, to, hashEqual)
+	if err != nil {
+		return nil, err
+	}
+
+	return newChanges(merkletrieChanges)
+}
+
+// check if the hash of the contents is different, if not, check if
+// the permissions are different (but taking into account deprecated
+// file modes).  On a treenoder, the hash of the contents is codified
+// in the first 20 bytes of the data returned by Hash() and the last
+// 4 bytes is the mode.
+func hashEqual(a, b noder.Hasher) bool {
+	hashA, hashB := a.Hash(), b.Hash()
+	contentsA, contentsB := hashA[:20], hashB[:20]
+
+	sameContents := bytes.Equal(contentsA, contentsB)
+	if !sameContents {
+		return false
+	}
+
+	modeA, modeB := hashA[20:], hashB[20:]
+
+	return equivalentMode(modeA, modeB)
+}
+
+func equivalentMode(a, b []byte) bool {
+	if isFilish(a) && isFilish(b) {
+		return true
+	}
+	return bytes.Equal(a, b)
+}
+
+var (
+	file           = modeToBytes(FileMode)
+	fileDeprecated = modeToBytes(FileModeDeprecated)
+	// remove this by fixing plumbing.Object mode ASAP
+	fileGoGit = modeToBytes(os.FileMode(0644))
+)
+
+func isFilish(b []byte) bool {
+	return bytes.Equal(b, file) ||
+		bytes.Equal(b, fileDeprecated) ||
+		bytes.Equal(b, fileGoGit)
+}