[clang-tools-extra] [clang-tidy] Document that check_clang_tidy.py needs unix diff (PR #214681)

[via cfe-commits]

https://github.com/richardmilles created https://github.com/llvm/llvm-project/pull/214681

Note that failed-fix dumps use the Unix `diff` command, which must be on PATH.

Fixes #31242

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>From 0c74375e29b56c8267d9eae795906815dcd06a1c Mon Sep 17 00:00:00 2001
From: richardmilles <darkenhalneke at gmail.com>
Date: Fri, 7 Aug 2026 10:17:06 +0200
Subject: [PATCH] [clang-tidy] Document that check_clang_tidy.py needs unix
 diff

Fixes #31242
---
 clang-tools-extra/test/clang-tidy/check_clang_tidy.py | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/clang-tools-extra/test/clang-tidy/check_clang_tidy.py b/clang-tools-extra/test/clang-tidy/check_clang_tidy.py
index 718ae361889ce..a0f157b0a11e1 100755
--- a/clang-tools-extra/test/clang-tidy/check_clang_tidy.py
+++ b/clang-tools-extra/test/clang-tidy/check_clang_tidy.py
@@ -1,4 +1,4 @@
-#!/usr/bin/env python3
+#!/usr/bin/env python3
 #
 # ===-----------------------------------------------------------------------===#
 #
@@ -37,6 +37,9 @@
 
 Notes
 -----
+  Failed-fix dumps use the Unix ``diff`` command (not ``git diff``); ensure
+  ``diff`` is available on PATH.
+
   -std=c++(98|11|14|17|20)-or-later:
     This flag will cause multiple runs within the same check_clang_tidy
     execution. Make sure you don't have shared state across these runs.