From ff65faa082f9eca3239da25277e1eb15bd3ac9ec Mon Sep 17 00:00:00 2001
From: joseferminj <joseferminj@gmail.com>
Date: Sat, 8 Nov 2014 19:07:21 -0500
Subject: [PATCH] Fix MergeTrees func to accept nil as ancestor parameter

---
 merge.go      | 13 +++++++++----
 merge_test.go | 23 +++++++++++++++++++++++
 2 files changed, 32 insertions(+), 4 deletions(-)

diff --git a/merge.go b/merge.go
index 2bc4e47..93ac71b 100644
--- a/merge.go
+++ b/merge.go
@@ -206,8 +206,11 @@ func (r *Repository) MergeTrees(ancestor *Tree, ours *Tree, theirs *Tree, option
 	copts := options.toC()
 
 	idx := &Index{}
-
-	ret := C.git_merge_trees(&idx.ptr, r.ptr, ancestor.cast_ptr, ours.cast_ptr, theirs.cast_ptr, copts)
+	var ancestor_ptr *C.git_tree
+	if ancestor != nil {
+		ancestor_ptr = ancestor.cast_ptr
+	}
+	ret := C.git_merge_trees(&idx.ptr, r.ptr, ancestor_ptr, ours.cast_ptr, theirs.cast_ptr, copts)
 	if ret < 0 {
 		return nil, MakeGitError(ret)
 	}
@@ -273,8 +276,10 @@ type MergeFileInput struct {
 // populate a C struct with merge file input, make sure to use freeMergeFileInput to clean up allocs
 func populateCMergeFileInput(c *C.git_merge_file_input, input MergeFileInput) {
 	c.path = C.CString(input.Path)
-	c.ptr = (*C.char)(unsafe.Pointer(&input.Contents[0]))
-	c.size = C.size_t(len(input.Contents))
+	if input.Contents != nil {
+		c.ptr = (*C.char)(unsafe.Pointer(&input.Contents[0]))
+		c.size = C.size_t(len(input.Contents))
+	}
 	c.mode = C.uint(input.Mode)
 }
 
diff --git a/merge_test.go b/merge_test.go
index cc7af81..7e884c0 100644
--- a/merge_test.go
+++ b/merge_test.go
@@ -1,6 +1,7 @@
 package git
 
 import (
+	"os"
 	"testing"
 )
 
@@ -64,6 +65,28 @@ func TestMergeSameFile(t *testing.T) {
 
 	compareBytes(t, file.Contents, result.Contents)
 
+}
+func TestMergeTreesWithoutAncestor(t *testing.T) {
+	repo := createTestRepo(t)
+	defer repo.Free()
+	defer os.RemoveAll(repo.Workdir())
+
+	_, originalTreeId := seedTestRepo(t, repo)
+	originalTree, err := repo.LookupTree(originalTreeId)
+
+	checkFatal(t, err)
+
+	_, newTreeId := updateReadme(t, repo, "file changed\n")
+
+	newTree, err := repo.LookupTree(newTreeId)
+	checkFatal(t, err)
+	index, err := repo.MergeTrees(nil, originalTree, newTree, nil)
+	if !index.HasConflicts() {
+		t.Fatal("expected conflicts in the index")
+	}
+	_, err = index.GetConflict("README")
+	checkFatal(t, err)
+
 }
 
 func compareBytes(t *testing.T, expected, actual []byte) {
-- 
2.45.2