[clang] [clang] Document -fstrict-flex-arrays option (PR #138388)

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https://github.com/serge-sans-paille updated https://github.com/llvm/llvm-project/pull/138388

>From 39cf81caaab7257414d72fae3afbb3baa8113b7f Mon Sep 17 00:00:00 2001
From: serge-sans-paille <sguelton at mozilla.com>
Date: Sat, 3 May 2025 10:10:09 +0200
Subject: [PATCH] [clang] Document -fstrict-flex-arrays option

Fix #138185
---
 clang/include/clang/Driver/Options.td | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
index 2946ffaa28da0..11677626dbf1f 100644
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -1554,7 +1554,11 @@ def fstrict_flex_arrays_EQ : Joined<["-"], "fstrict-flex-arrays=">, Group<f_Grou
   Visibility<[ClangOption, CC1Option]>,
   NormalizedValuesScope<"LangOptions::StrictFlexArraysLevelKind">,
   NormalizedValues<["Default", "OneZeroOrIncomplete", "ZeroOrIncomplete", "IncompleteOnly"]>,
-  HelpText<"Enable optimizations based on the strict definition of flexible arrays">,
+  HelpText<"Enable optimizations based on the strict definition of flexible arrays.">,
+  DocBrief<[{If ``<n>`` is equal to 0, any trailing array member is considered a flexible array.
+             If ``<n>`` is equal to 1, trailing array members of size 0, 1 or undefined are considered flexible arrays.
+             If ``<n>`` is equal to 2, trailing array members of size 0 or undefined are considered flexible arrays.
+             If ``<n>`` is equal to 3, only trailing array members of undefined size are considered flexible arrays.}]>,
   MarshallingInfoEnum<LangOpts<"StrictFlexArraysLevel">, "Default">;
 defm apple_pragma_pack : BoolFOption<"apple-pragma-pack",
   LangOpts<"ApplePragmaPack">, DefaultFalse,