This is related to the C++ compatibility work in [0].
This patch proposes to use the standard C23 and C++ attributes
[[nodiscard]], [[noreturn]], and [[maybe_unused]], if available.
The immediate practical impact is that for pg_noreturn, we can drop the
GCC-specific and MSVC-specific fallbacks, because the C11 and the C++
implementation will now cover all required cases.
For the other two attributes, this makes them available in
not-GCC-compatible compilers that support C23 as well as in C++. This
set is theoretical at the moment, but it might become more practical if
either MSVC gets some C23 support or we improve the support for C++
extensions with MSVC (see also [0]).
[0]:
https://www.postgresql.org/message-id/df78eaac-c2eb-4344-852e-0965c75c5ad6%40eisentraut.orgFrom 662e74060acb710edf2b56084519f1b951835cab Mon Sep 17 00:00:00 2001
From: Peter Eisentraut <[email protected]>
Date: Thu, 19 Feb 2026 09:42:19 +0100
Subject: [PATCH] Use standard C23 and C++ attributes if available
Use the standard C23 and C++ attributes [[nodiscard]], [[noreturn]],
and [[maybe_unused]], if available.
This makes pg_nodiscard and pg_attribute_unused() available in
not-GCC-compatible compilers that support C23 as well as in
C++ (although this set is theoretical at this point).
For pg_noreturn, we can now drop the GCC-specific and MSVC-specific
fallbacks, because the C11 and the C++ implementation will now cover
all required cases.
Note, in a few places, we need to change the position of the attribute
because it's not valid in that place in C23.
Discussion:
https://www.postgresql.org/message-id/flat/pxr5b3z7jmkpenssra5zroxi7qzzp6eswuggokw64axmdixpnk@zbwxuq7gbbcw
---
src/backend/utils/mmgr/slab.c | 2 +-
src/include/c.h | 38 ++++++++++++++----------
src/include/lib/radixtree.h | 2 +-
src/test/modules/worker_spi/worker_spi.c | 2 +-
4 files changed, 25 insertions(+), 19 deletions(-)
diff --git a/src/backend/utils/mmgr/slab.c b/src/backend/utils/mmgr/slab.c
index bd00bab18fe..34a9410e76a 100644
--- a/src/backend/utils/mmgr/slab.c
+++ b/src/backend/utils/mmgr/slab.c
@@ -628,8 +628,8 @@ SlabAllocFromNewBlock(MemoryContext context, Size size, int
flags)
* to setup the stack frame in SlabAlloc. For performance
reasons, we
* want to avoid that.
*/
-pg_noinline
pg_noreturn
+pg_noinline
static void
SlabAllocInvalidSize(MemoryContext context, Size size)
{
diff --git a/src/include/c.h b/src/include/c.h
index a249674f026..8c6182a2c8e 100644
--- a/src/include/c.h
+++ b/src/include/c.h
@@ -111,6 +111,8 @@
/*
* Attribute macros
*
+ * C23: https://en.cppreference.com/w/c/language/attributes.html
+ * C++: https://en.cppreference.com/w/cpp/language/attributes.html
* GCC: https://gcc.gnu.org/onlinedocs/gcc/Function-Attributes.html
* GCC: https://gcc.gnu.org/onlinedocs/gcc/Type-Attributes.html
* Clang: https://clang.llvm.org/docs/AttributeReference.html
@@ -120,13 +122,20 @@
* For compilers which don't support __has_attribute, we just define
* __has_attribute(x) to 0 so that we can define macros for various
* __attribute__s more easily below.
+ *
+ * Note that __has_attribute only tells about GCC-style attributes, not C23 or
+ * C++ attributes.
*/
#ifndef __has_attribute
#define __has_attribute(attribute) 0
#endif
-/* only GCC supports the unused attribute */
-#ifdef __GNUC__
+/*
+ * pg_attribute_unused() suppresses compiler warnings on unused entities.
+ */
+#if (defined(__STDC_VERSION__) && __STDC_VERSION__ >= 202311L) ||
(defined(__cplusplus) && __cplusplus >= 201703L)
+#define pg_attribute_unused() [[maybe_unused]]
+#elif defined(__GNUC__)
#define pg_attribute_unused() __attribute__((unused))
#else
#define pg_attribute_unused()
@@ -134,11 +143,11 @@
/*
* pg_nodiscard means the compiler should warn if the result of a function
- * call is ignored. The name "nodiscard" is chosen in alignment with the C23
- * standard attribute with the same name. For maximum forward compatibility,
- * place it before the declaration.
+ * call is ignored.
*/
-#ifdef __GNUC__
+#if (defined(__STDC_VERSION__) && __STDC_VERSION__ >= 202311L) ||
(defined(__cplusplus) && __cplusplus >= 201703L)
+#define pg_nodiscard [[nodiscard]]
+#elif defined(__GNUC__)
#define pg_nodiscard __attribute__((warn_unused_result))
#else
#define pg_nodiscard
@@ -150,18 +159,15 @@
* uses __attribute__((noreturn)) in headers, which would get confused if
* "noreturn" is defined to "_Noreturn", as is done by <stdnoreturn.h>.
*
- * In a declaration, function specifiers go before the function name. The
- * common style is to put them before the return type. (The MSVC fallback has
- * the same requirement. The GCC fallback is more flexible.)
+ * C23 attributes must be placed at the start of a declaration or statement.
+ * C11 function specifiers go before the function name in a declaration, but
+ * it is common style (and required for C23 compatibility) to put them before
+ * the return type.
*/
-#if (defined(__STDC_VERSION__) && __STDC_VERSION__ >= 201112L) &&
!defined(__cplusplus)
-#define pg_noreturn _Noreturn
-#elif defined(__GNUC__)
-#define pg_noreturn __attribute__((noreturn))
-#elif defined(_MSC_VER)
-#define pg_noreturn __declspec(noreturn)
+#if (defined(__STDC_VERSION__) && __STDC_VERSION__ >= 202311L) ||
defined(__cplusplus)
+#define pg_noreturn [[noreturn]]
#else
-#define pg_noreturn
+#define pg_noreturn _Noreturn
#endif
/*
diff --git a/src/include/lib/radixtree.h b/src/include/lib/radixtree.h
index b223ce10a2d..179f78137fa 100644
--- a/src/include/lib/radixtree.h
+++ b/src/include/lib/radixtree.h
@@ -2777,8 +2777,8 @@ RT_STATS(RT_RADIX_TREE * tree)
/*
* Print out debugging information about the given node.
*/
-static void
pg_attribute_unused()
+static void
RT_DUMP_NODE(RT_NODE * node)
{
#ifdef RT_SHMEM
diff --git a/src/test/modules/worker_spi/worker_spi.c
b/src/test/modules/worker_spi/worker_spi.c
index d1e4a2bd952..f9bb16a017e 100644
--- a/src/test/modules/worker_spi/worker_spi.c
+++ b/src/test/modules/worker_spi/worker_spi.c
@@ -44,7 +44,7 @@ PG_MODULE_MAGIC;
PG_FUNCTION_INFO_V1(worker_spi_launch);
-PGDLLEXPORT pg_noreturn void worker_spi_main(Datum main_arg);
+pg_noreturn PGDLLEXPORT void worker_spi_main(Datum main_arg);
/* GUC variables */
static int worker_spi_naptime = 10;
--
2.53.0
