[clang] [clang][Sema] Add regression test for invalid friend declaration (PR #224798)

[Jeewoong Kim via cfe-commits]

https://github.com/JeewoongKim created https://github.com/llvm/llvm-project/pull/224798

Added a regression test for #132614.

The original fuzzer reproducer no longer crashes on `main`.
This adds coverage for the friend function declaration path, which is not covered by
the existing test in `class.friend/p6.cpp`.

Tested `clang/test/CXX/class/class.friend/p6.cpp` locally.

>From 76ded6058eeff10094227be17d7d508c18083348 Mon Sep 17 00:00:00 2001
From: Jeewoong Kim <dnd414 at gmail.com>
Date: Sat, 19 Sep 2026 12:44:23 +0900
Subject: [PATCH] [clang][Sema] Add regression test for invalid friend
 declaration

---
 clang/test/CXX/class/class.friend/p6.cpp | 1 +
 1 file changed, 1 insertion(+)

diff --git a/clang/test/CXX/class/class.friend/p6.cpp b/clang/test/CXX/class/class.friend/p6.cpp
index a96dd8a3d4e4a..2152c87e38ef6 100644
--- a/clang/test/CXX/class/class.friend/p6.cpp
+++ b/clang/test/CXX/class/class.friend/p6.cpp
@@ -20,4 +20,5 @@ class A {
   friend thread_local class G; // expected-error {{'thread_local' is invalid in friend declarations}}
 #endif
   friend register enum; // expected-error {{expected identifier or '{'}} expected-error {{'register' is invalid in friend declarations}}
+  friend static unknown foo(); // expected-error {{unknown type name 'unknown'}} expected-error {{'static' is invalid in friend declarations}}
 };