[libcxx-commits] [libcxx] [AIX][libc++] Fix redefinition of wchar_t overloads on AIX (PR #201432)

[via libcxx-commits]

https://github.com/Himadhith created https://github.com/llvm/llvm-project/pull/201432

On AIX, the system headers have a circular dependency: `wctype.h → wchar.h → wctype.h` which causes wchar.h to be processed multiple times. 

The existing `_LIBCPP_WCHAR_H` include guard does not protect because wchar.h is a textual header and they get their own pre-processing per module compilation. 

>From e8303d979af9fb0e60da06627dcce88465ec1bbf Mon Sep 17 00:00:00 2001
From: himadhith <himadhith.v at ibm.com>
Date: Wed, 3 Jun 2026 14:48:19 -0400
Subject: [PATCH] [AIX][libc++] Fix redefinition of wchar_t overloads on AIX

---
 libcxx/include/wchar.h                                    | 2 ++
 libcxx/test/extensions/clang/clang_modules_include.gen.py | 2 --
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/libcxx/include/wchar.h b/libcxx/include/wchar.h
index a932dd266b862..8f652fee873fc 100644
--- a/libcxx/include/wchar.h
+++ b/libcxx/include/wchar.h
@@ -137,6 +137,7 @@ size_t wcsrtombs(char* restrict dst, const wchar_t** restrict src, size_t len,
 
 #    if _LIBCPP_HAS_WIDE_CHARACTERS
 #      if defined(__cplusplus) && !defined(_LIBCPP_WCHAR_H_HAS_CONST_OVERLOADS) && defined(_LIBCPP_PREFERRED_OVERLOAD)
+#       if defined(_AIX) && !defined(_LIBCPP_WCHAR_H_OVERLOADS)
 extern "C++" {
 inline _LIBCPP_HIDE_FROM_ABI wchar_t* __libcpp_wcschr(const wchar_t* __s, wchar_t __c) {
   return (wchar_t*)wcschr(__s, __c);
@@ -200,6 +201,7 @@ size_t mbsnrtowcs(
 size_t wcsnrtombs(
     char* __restrict __dst, const wchar_t** __restrict __src, size_t __nwc, size_t __len, mbstate_t* __restrict __ps);
 } // extern "C"
+#       endif // _LIBCPP_WCHAR_H_OVERLOADS
 #      endif // __cplusplus && (_LIBCPP_MSVCRT || __MVS__)
 #    endif   // _LIBCPP_HAS_WIDE_CHARACTERS
 #  endif     // _LIBCPP_WCHAR_H
diff --git a/libcxx/test/extensions/clang/clang_modules_include.gen.py b/libcxx/test/extensions/clang/clang_modules_include.gen.py
index 28661049d6e85..f0de60bacd7a7 100644
--- a/libcxx/test/extensions/clang/clang_modules_include.gen.py
+++ b/libcxx/test/extensions/clang/clang_modules_include.gen.py
@@ -30,8 +30,6 @@
 # TODO: Investigate why this doesn't work on Picolibc once the locale base API is refactored
 # UNSUPPORTED: LIBCXX-PICOLIBC-FIXME
 
-# TODO: Fix seemingly circular inclusion or <wchar.h> on AIX
-# UNSUPPORTED: LIBCXX-AIX-FIXME
 
 # UNSUPPORTED: FROZEN-CXX03-HEADERS-FIXME