fix: ignore mnemonic diff prefixes in patches

Author: pick7

git/diff.py

@@ -284,7 +284,10 @@ def diff(
         # END paths handling
 
         kwargs["as_process"] = True
-        proc = diff_cmd(*self._process_diff_args(args), **kwargs)
+        args = self._process_diff_args(args)
+        if create_patch:
+            self.repo.git(c="diff.mnemonicPrefix=false")
+        proc = diff_cmd(*args, **kwargs)
 
         diff_method = Diff._index_from_patch_format if create_patch else Diff._index_from_raw_format
         index = diff_method(self.repo, proc)

git/index/base.py

@@ -1547,6 +1547,8 @@ def diff(
                 args.extend(paths)
 
             kwargs["as_process"] = True
+            if create_patch:
+                self.repo.git(c="diff.mnemonicPrefix=false")
             proc = self.repo.git.diff(*args, **kwargs)
 
             diff_method = (

test/test_diff.py

@@ -92,6 +92,26 @@ def test_diff_with_staged_file(self, rw_dir):
             "This should work, but doesn't right now ... it's OK",
         )
 
+    @with_rw_directory
+    def test_patch_diff_ignores_mnemonic_prefix(self, rw_dir):
+        repo = Repo.init(rw_dir)
+        filepath = osp.join(rw_dir, "file.txt")
+        with open(filepath, "w") as stream:
+            stream.write("initial\n")
+        repo.index.add([filepath])
+        repo.index.commit("initial")
+
+        with open(filepath, "w") as stream:
+            stream.write("changed\n")
+        repo.git.config("diff.mnemonicPrefix", "true")
+
+        self.assertEqual(len(repo.head.commit.diff(None, create_patch=True)), 1)
+        self.assertEqual(len(repo.index.diff(None, create_patch=True)), 1)
+
+        repo.index.add([filepath])
+        self.assertEqual(len(repo.index.diff(NULL_TREE, create_patch=True)), 1)
+        self.assertEqual(repo.git.config("--get", "diff.mnemonicPrefix"), "true")
+
     def test_list_from_string_new_mode(self):
         output = StringProcessAdapter(fixture("diff_new_mode"))
         diffs = Diff._index_from_patch_format(self.rorepo, output)