Find tree entry by id

Add support for 'git_tree_entry_byid'.

tree.go

@@ -55,6 +55,24 @@ func (t Tree) EntryByName(filename string) *TreeEntry {
 	return newTreeEntry(entry)
 }
 
+// EntryById performs a lookup for a tree entry with the given SHA value.
+//
+// It returns a *TreeEntry that is owned by the Tree. You don't have to
+// free it, but you must not use it after the Tree is freed.
+//
+// Warning: this must examine every entry in the tree, so it is not fast.
+func (t Tree) EntryById(id *Oid) *TreeEntry {
+	runtime.LockOSThread()
+	defer runtime.UnlockOSThread()
+
+	entry := C.git_tree_entry_byid(t.cast_ptr, id.toC())
+	if entry == nil {
+		return nil
+	}
+
+	return newTreeEntry(entry)
+}
+
 // EntryByPath looks up an entry by its full path, recursing into
 // deeper trees if necessary (i.e. if there are slashes in the path)
 func (t Tree) EntryByPath(path string) (*TreeEntry, error) {

tree_test.go

@@ -0,0 +1,22 @@
+package git
+
+import "testing"
+
+func TestTreeEntryById(t *testing.T) {
+	repo := createTestRepo(t)
+	defer cleanupTestRepo(t, repo)
+
+	_, treeID := seedTestRepo(t, repo)
+
+	tree, err := repo.LookupTree(treeID)
+	checkFatal(t, err)
+
+	id, err := NewOid("257cc5642cb1a054f08cc83f2d943e56fd3ebe99")
+	checkFatal(t, err)
+
+	entry := tree.EntryById(id)
+
+	if entry == nil {
+		t.Fatalf("entry id %v was not found", id)
+	}
+}