[clang] Generate empty .clang-format-ignore before running tests (PR #136154)

[Devon Loehr via cfe-commits]

https://github.com/DKLoehr created https://github.com/llvm/llvm-project/pull/136154

Followup to #136022, this ensures formatting tests are run with an empty `.clang-format-ignore` in their root directory, to prevent failures if the file also exists higher in the tree.

>From 804fcdd84e8551005bfa5dae58d24f9852608360 Mon Sep 17 00:00:00 2001
From: Devon Loehr <dloehr at google.com>
Date: Thu, 17 Apr 2025 16:10:55 +0000
Subject: [PATCH] Generate empty .clang-format-ignore before running tests

---
 clang/test/Format/lit.local.cfg | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/clang/test/Format/lit.local.cfg b/clang/test/Format/lit.local.cfg
index b060c79226cbd..cf79e8df89a33 100644
--- a/clang/test/Format/lit.local.cfg
+++ b/clang/test/Format/lit.local.cfg
@@ -1,3 +1,4 @@
+import os
 import platform
 import lit.formats
 
@@ -27,3 +28,8 @@ config.suffixes = [
 # python implementation does, so use that for cross platform compatibility
 if platform.system() == "AIX":
     config.test_format = lit.formats.ShTest()
+
+# Create an empty .clang-format-ignore file so that tests don't get messed
+# up if one exists higher in the tree
+with open(os.path.join("Format", ".clang-format-ignore"), 'w'):
+    pass
\ No newline at end of file