From 7a8ba96c29b66e0c1d11c6bc885ac6efbd06a115 Mon Sep 17 00:00:00 2001
From: Stefan Gangefors <stefan@gangefors.se>
Date: Tue, 27 Mar 2018 17:36:15 +0200
Subject: [PATCH 1/2] Enable git diff-tree with empty second tree-ish param

Executing `git diff-tree` and omitting the second tree-ish argument
wasn't possible before. This commit enables this behaviour by allowing
the caller to send in an empty string.

Allowing an empty string keeps backwards compatibility for all other
allowed input types.
---
 AUTHORS               |  1 +
 git/diff.py           |  4 +++-
 git/test/test_diff.py | 14 ++++++++++++++
 3 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/AUTHORS b/AUTHORS
index b5f0ebdc1..6b78aeefd 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -26,5 +26,6 @@ Contributors are:
 -Mikuláš Poul <mikulaspoul _at_ gmail.com>
 -Charles Bouchard-Légaré <cblegare.atl _at_ ntis.ca>
 -Yaroslav Halchenko <debian _at_ onerussian.com>
+-Stefan Gangefors
 
 Portions derived from other open source works and are clearly marked.
diff --git a/git/diff.py b/git/diff.py
index d7221ac7d..bf56169c4 100644
--- a/git/diff.py
+++ b/git/diff.py
@@ -82,6 +82,7 @@ def diff(self, other=Index, paths=None, create_patch=False, **kwargs):
         :param other:
             Is the item to compare us with.
             If None, we will be compared to the working tree.
+            If empty string, it will be compared to it's parent with diff-tree.
             If Treeish, it will be compared against the respective tree
             If Index ( type ), it will be compared against the index.
             If git.NULL_TREE, it will compare against the empty tree.
@@ -132,7 +133,8 @@ def diff(self, other=Index, paths=None, create_patch=False, **kwargs):
             diff_cmd = self.repo.git.diff_tree
         elif other is not None:
             args.insert(0, '-r')  # recursive diff-tree
-            args.insert(0, other)
+            if other != '':
+                args.insert(0, other)
             diff_cmd = self.repo.git.diff_tree
 
         args.insert(0, self)
diff --git a/git/test/test_diff.py b/git/test/test_diff.py
index d21dde624..8d3ee63e3 100644
--- a/git/test/test_diff.py
+++ b/git/test/test_diff.py
@@ -266,3 +266,17 @@ def test_diff_interface(self):
         cp = c.parents[0]
         diff_index = c.diff(cp, ["does/not/exist"])
         self.assertEqual(len(diff_index), 0)
+
+    def test_diff_tree_empty_other(self):
+        initial_commit = self.rorepo.commit('9066712dca21ef35c534e068f2cc4fefdccf1ea3')
+
+        # Test that we can use an empty string as other in a diff.
+        # It should do a diff-tree without the second tree-ish param
+        diff_index = initial_commit.diff('')
+        self.assertEqual(len(diff_index), 16)
+        self.assertEqual(diff_index[0].change_type, 'M')
+        self.assertTrue(diff_index[12].deleted_file)
+        self.assertTrue(diff_index[14].renamed)
+        self.assertEqual(diff_index[14].rename_from, 'test/asserts.py')
+        self.assertEqual(diff_index[14].rename_to, 'test/testlib/asserts.py')
+        self.assertEqual(diff_index[15].change_type, 'A')

From 4669d6d1fcc67d64f55fe850cd6c43893d44836d Mon Sep 17 00:00:00 2001
From: Stefan Gangefors <stefan@gangefors.se>
Date: Tue, 27 Mar 2018 17:43:28 +0200
Subject: [PATCH 2/2] Fix docstring for git.diff.diff()

---
 git/diff.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/git/diff.py b/git/diff.py
index bf56169c4..a69c0926d 100644
--- a/git/diff.py
+++ b/git/diff.py
@@ -81,7 +81,7 @@ def diff(self, other=Index, paths=None, create_patch=False, **kwargs):
 
         :param other:
             Is the item to compare us with.
-            If None, we will be compared to the working tree.
+            If None, it will be compared to the working tree.
             If empty string, it will be compared to it's parent with diff-tree.
             If Treeish, it will be compared against the respective tree
             If Index ( type ), it will be compared against the index.