difftree: ignore permissions changes between regular files

Fix issue #279.

1 files changed, 39 insertions, 1 deletions

diff --git a/plumbing/difftree/difftree.go b/plumbing/difftree/difftree.go
index d38ad2c..ff1ceaf 100644
--- a/plumbing/difftree/difftree.go
+++ b/plumbing/difftree/difftree.go
@@ -2,12 +2,15 @@ package difftree
 
 import (
 	"bytes"
+	"os"
 
 	"srcd.works/go-git.v4/plumbing/object"
 	"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 *object.Tree) ([]*Change, error) {
 	from := newTreeNoder(a)
 	to := newTreeNoder(b)
@@ -20,6 +23,41 @@ func DiffTree(a, b *object.Tree) ([]*Change, error) {
 	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 {
-	return bytes.Equal(a.Hash(), b.Hash())
+	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(object.FileMode)
+	fileDeprecated = modeToBytes(object.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)
 }