3 files changed, 28 insertions, 4 deletions
diff --git a/plumbing/format/index/encoder.go b/plumbing/format/index/encoder.go
index e5de135..4699d43 100644
--- a/plumbing/format/index/encoder.go
+++ b/plumbing/format/index/encoder.go
@@ -6,6 +6,7 @@ import (
 	"errors"
 	"hash"
 	"io"
+	"sort"
 	"time"
 
 	"srcd.works/go-git.v4/utils/binary"
@@ -61,6 +62,8 @@ func (e *Encoder) encodeHeader(idx *Index) error {
 }
 
 func (e *Encoder) encodeEntries(idx *Index) error {
+	sort.Sort(ByName(idx.Entries))
+
 	for _, entry := range idx.Entries {
 		if err := e.encodeEntry(&entry); err != nil {
 			return err
@@ -139,3 +142,9 @@ func (e *Encoder) padEntry(wrote int) error {
 func (e *Encoder) encodeFooter() error {
 	return binary.Write(e.w, e.hash.Sum(nil))
 }
+
+type ByName []Entry
+
+func (l ByName) Len() int           { return len(l) }
+func (l ByName) Swap(i, j int)      { l[i], l[j] = l[j], l[i] }
+func (l ByName) Less(i, j int) bool { return l[i].Name < l[j].Name }
diff --git a/plumbing/format/index/encoder_test.go b/plumbing/format/index/encoder_test.go
index 914ee26..a6a0ea2 100644
--- a/plumbing/format/index/encoder_test.go
+++ b/plumbing/format/index/encoder_test.go
@@ -26,6 +26,11 @@ func (s *IndexSuite) TestEncode(c *C) {
 		}, {
 			CreatedAt:  time.Now(),
 			ModifiedAt: time.Now(),
+			Name:       "bar",
+			Size:       82,
+		}, {
+			CreatedAt:  time.Now(),
+			ModifiedAt: time.Now(),
 			Name:       strings.Repeat(" ", 20),
 			Size:       82,
 		}},
@@ -42,6 +47,11 @@ func (s *IndexSuite) TestEncode(c *C) {
 	c.Assert(err, IsNil)
 
 	c.Assert(idx, DeepEquals, output)
+
+	c.Assert(output.Entries[0].Name, Equals, strings.Repeat(" ", 20))
+	c.Assert(output.Entries[1].Name, Equals, "bar")
+	c.Assert(output.Entries[2].Name, Equals, "foo")
+
 }
 
 func (s *IndexSuite) TestEncodeUnsuportedVersion(c *C) {
diff --git a/plumbing/format/index/index.go b/plumbing/format/index/index.go
index e5dc178..a95dba2 100644
--- a/plumbing/format/index/index.go
+++ b/plumbing/format/index/index.go
@@ -36,9 +36,14 @@ const (
 // in the worktree, having information about the working files. Changes in
 // worktree are detected using this Index. The Index is also used during merges
 type Index struct {
-	Version     uint32
-	Entries     []Entry
-	Cache       *Tree
+	// Version is index version
+	Version uint32
+	// Entries collection of entries represented by this Index. The order of
+	// this collection is not guaranteed
+	Entries []Entry
+	// Cache represents the 'Cached tree' extension
+	Cache *Tree
+	// ResolveUndo represents the 'Resolve undo' extension
 	ResolveUndo *ResolveUndo
 }
 
@@ -84,7 +89,7 @@ type TreeEntry struct {
 	// Path component (relative to its parent directory)
 	Path string
 	// Entries is the number of entries in the index that is covered by the tree
-	// this entry represents
+	// this entry represents.
 	Entries int
 	// Trees is the number that represents the number of subtrees this tree has
 	Trees int