[libcxx-commits] [libcxx] [libcxx][modules] Ensure that __new/align_val_t.h always contains align_val_t (PR #158781)

[via libcxx-commits]

https://github.com/matts1 updated https://github.com/llvm/llvm-project/pull/158781

>From 453c9451f48c3e87bcee12151f5b54eac3c22a6d Mon Sep 17 00:00:00 2001
From: Matt Stark <msta at google.com>
Date: Tue, 16 Sep 2025 05:38:02 +0000
Subject: [PATCH] [libcxx][modules] Ensure that __new/align_val_t.h always
 contains std::align_val_t.

Previously, I was getting the following error when attempting to compile
libc++ on windows with modules enabled.

```
While building module 'std':
In file included from <module-includes>:1:
In file included from gen/third_party/libc++/src/include/algorithm:1865:
In file included from gen/third_party/libc++/src/include/__algorithm/inplace_merge.h:28:
In file included from gen/third_party/libc++/src/include/__memory/unique_temporary_buffer.h:17:
In file included from gen/third_party/libc++/src/include/__memory/allocator.h:19:
gen/third_party/libc++/src/include/__new/allocate.h(40,73): error:
      declaration of 'align_val_t' must be imported from module
      'sys_stage1.sysroot_vcruntime_new_h' before it is required
   40 |     return static_cast<_Tp*>(__builtin_operator_new(__size, static_cast<align_val...
      |                                                                         ^
../../third_party/depot_tools/win_toolchain/vs_files/e4305f407e/VC/Tools/MSVC/14.44.35207/include/vcruntime_new.h(27,33): note:
      declaration here is not visible
   27 |     _VCRT_EXPORT_STD enum class align_val_t : size_t {};
      |                                 ^
```
---
 libcxx/include/__new/align_val_t.h | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/libcxx/include/__new/align_val_t.h b/libcxx/include/__new/align_val_t.h
index 03ab7cb143a2b..93f673431bfea 100644
--- a/libcxx/include/__new/align_val_t.h
+++ b/libcxx/include/__new/align_val_t.h
@@ -16,14 +16,19 @@
 #  pragma GCC system_header
 #endif
 
+#if _LIBCPP_HAS_LIBRARY_ALIGNED_ALLOCATION
+#  if defined(_LIBCPP_ABI_VCRUNTIME)
+// std::align_val_t is defined in vcruntime_new.h
+#    include <vcruntime_new.h>
+#  else
 _LIBCPP_BEGIN_UNVERSIONED_NAMESPACE_STD
-#if _LIBCPP_HAS_LIBRARY_ALIGNED_ALLOCATION && !defined(_LIBCPP_ABI_VCRUNTIME)
-#  ifndef _LIBCPP_CXX03_LANG
+#    ifndef _LIBCPP_CXX03_LANG
 enum class align_val_t : size_t {};
-#  else
+#    else
 enum align_val_t { __zero = 0, __max = (size_t)-1 };
+#    endif
+_LIBCPP_END_UNVERSIONED_NAMESPACE_STD
 #  endif
 #endif
-_LIBCPP_END_UNVERSIONED_NAMESPACE_STD
 
 #endif // _LIBCPP___NEW_ALIGN_VAL_T_H