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

[via libcxx-commits]

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

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 {};
      |                                 ^
```

>From 86f27e30fad559c491a2e4df653aca4a757a6b9f 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: 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 | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/libcxx/include/__new/align_val_t.h b/libcxx/include/__new/align_val_t.h
index 03ab7cb143a2b..36fc9f3365062 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
 enum class align_val_t : size_t {};
 #  else
 enum align_val_t { __zero = 0, __max = (size_t)-1 };
 #  endif
-#endif
 _LIBCPP_END_UNVERSIONED_NAMESPACE_STD
+#endif
+#endif
 
 #endif // _LIBCPP___NEW_ALIGN_VAL_T_H