From 7654e1a50e9e5e92768218cf624ec5e9c0469f9e Mon Sep 17 00:00:00 2001
From: Philipp Hahn <hahn@univention.de>
Date: Fri, 20 Jan 2023 11:48:42 +0100
Subject: [PATCH] fix(git): Use diff-tree instead of diff

which does not require all intermediate commits to exists, which helps
when running from CI/CD pipelines which do shallow clones for
performance reasons.

Inspired by
<https://forum.gitlab.com/t/ci-cd-pipeline-get-list-of-changed-files/26847/25>
---
 pre_commit/git.py | 13 +++++--------
 1 file changed, 5 insertions(+), 8 deletions(-)

diff --git a/pre_commit/git.py b/pre_commit/git.py
index 333dc7ba..3ac9acd9 100644
--- a/pre_commit/git.py
+++ b/pre_commit/git.py
@@ -156,14 +156,11 @@ def get_all_files() -> list[str]:
 
 
 def get_changed_files(old: str, new: str) -> list[str]:
-    diff_cmd = ('git', 'diff', '--name-only', '--no-ext-diff', '-z')
-    try:
-        _, out, _ = cmd_output(*diff_cmd, f'{old}...{new}')
-    except CalledProcessError:  # pragma: no cover (new git)
-        # on newer git where old and new do not have a merge base git fails
-        # so we try a full diff (this is what old git did for us!)
-        _, out, _ = cmd_output(*diff_cmd, f'{old}..{new}')
-
+    _, out, _ = cmd_output(
+        'git', 'diff-tree',
+        '--name-only', '--raw', '-z',
+        old, new,
+    )
     return zsplit(out)