https://github.com/AaronBallman created
https://github.com/llvm/llvm-project/pull/154599
The C++ standard requires stddef.h to declare all of its contents in the global
namespace. We were only doing it when trying to be compatible with Microsoft
extensions. Now we expose in C++11 or later, in addition to exposing it in
Microsoft extensions mode.
Fixes #154577
>From db02621cf7bf7fcd71f5b172d06b176fda296faa Mon Sep 17 00:00:00 2001
From: Aaron Ballman <aa...@aaronballman.com>
Date: Wed, 20 Aug 2025 15:05:40 -0400
Subject: [PATCH] [C++] Expose nullptr_t from stddef.h in C++ mode
The C++ standard requires stddef.h to declare all of its contents in
the global namespace. We were only doing it when trying to be
compatible with Microsoft extensions. Now we expose in C++11 or later,
in addition to exposing it in Microsoft extensions mode.
Fixes #154577
---
clang/docs/ReleaseNotes.rst | 1 +
clang/lib/Headers/__stddef_nullptr_t.h | 3 ++-
clang/test/Headers/stddefneeds.cpp | 26 +++++++++++++++++++++++++-
3 files changed, 28 insertions(+), 2 deletions(-)
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 77629c074cdcd..bceeb63d048c8 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -223,6 +223,7 @@ Bug Fixes in This Version
cast chain. (#GH149967).
- Fixed a crash with incompatible pointer to integer conversions in designated
initializers involving string literals. (#GH154046)
+- Clang's ``<stddef.h>`` now properly declares ``nullptr_t`` in C++ mode.
(#GH154577).
Bug Fixes to Compiler Builtins
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/clang/lib/Headers/__stddef_nullptr_t.h
b/clang/lib/Headers/__stddef_nullptr_t.h
index 7f3fbe6fe0d3a..c84b7bc2dc198 100644
--- a/clang/lib/Headers/__stddef_nullptr_t.h
+++ b/clang/lib/Headers/__stddef_nullptr_t.h
@@ -16,7 +16,8 @@
#define _NULLPTR_T
#ifdef __cplusplus
-#if defined(_MSC_EXTENSIONS) && defined(_NATIVE_NULLPTR_SUPPORTED)
+#if __cplusplus >= 201103L ||
\
+ (defined(_MSC_EXTENSIONS) && defined(_NATIVE_NULLPTR_SUPPORTED))
namespace std {
typedef decltype(nullptr) nullptr_t;
}
diff --git a/clang/test/Headers/stddefneeds.cpp
b/clang/test/Headers/stddefneeds.cpp
index 0282e8afa600d..6e8829bc1be67 100644
--- a/clang/test/Headers/stddefneeds.cpp
+++ b/clang/test/Headers/stddefneeds.cpp
@@ -1,10 +1,12 @@
// RUN: %clang_cc1 -fsyntax-only -triple x86_64-apple-macosx10.9.0 -verify
-Wsentinel -std=c++11 %s
+// RUN: %clang_cc1 -fsyntax-only -triple x86_64-apple-macosx10.9.0
-verify=old,expected -Wsentinel -std=c++98 %s
ptrdiff_t p0; // expected-error{{unknown}}
size_t s0; // expected-error{{unknown}}
void* v0 = NULL; // expected-error{{undeclared}}
wint_t w0; // expected-error{{unknown}}
max_align_t m0; // expected-error{{unknown}}
+nullptr_t n0; // expected-error {{unknown}}
#define __need_ptrdiff_t
#include <stddef.h>
@@ -14,6 +16,7 @@ size_t s1; // expected-error{{unknown}}
void* v1 = NULL; // expected-error{{undeclared}}
wint_t w1; // expected-error{{unknown}}
max_align_t m1; // expected-error{{unknown}}
+nullptr_t n1; // expected-error{{unknown}}
#define __need_size_t
#include <stddef.h>
@@ -23,6 +26,16 @@ size_t s2;
void* v2 = NULL; // expected-error{{undeclared}}
wint_t w2; // expected-error{{unknown}}
max_align_t m2; // expected-error{{unknown}}
+nullptr_t n2; // expected-error{{unknown}}
+
+#define __need_nullptr_t
+#include <stddef.h>
+ptrdiff_t p6;
+size_t s6;
+void* v6 = NULL; // expected-error{{undeclared}}
+wint_t w6; // expected-error{{unknown}}
+max_align_t m6; // expected-error{{unknown}}
+nullptr_t n6; // old-error{{unknown}}
#define __need_NULL
#include <stddef.h>
@@ -32,6 +45,16 @@ size_t s3;
void* v3 = NULL;
wint_t w3; // expected-error{{unknown}}
max_align_t m3; // expected-error{{unknown}}
+nullptr_t n3; // old-error{{unknown}}
+
+#define __need_max_align_t
+#include <stddef.h>
+ptrdiff_t p7;
+size_t s7;
+void* v7 = NULL;
+wint_t w7; // expected-error{{unknown}}
+max_align_t m7;
+nullptr_t n7; // old-error{{unknown}}
// Shouldn't bring in wint_t by default:
#include <stddef.h>
@@ -41,6 +64,7 @@ size_t s4;
void* v4 = NULL;
wint_t w4; // expected-error{{unknown}}
max_align_t m4;
+nullptr_t n4; // old-error{{unknown}}
#define __need_wint_t
#include <stddef.h>
@@ -50,7 +74,7 @@ size_t s5;
void* v5 = NULL;
wint_t w5;
max_align_t m5;
-
+nullptr_t n5; // old-error{{unknown}}
// linux/stddef.h does something like this for cpp files:
#undef NULL
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