[PATCH v2] ginclude: Add comments to <stdalign.h> and <stdbool.h> about deprecated macros

[Jonathan Wakely]

On Fri, 25 Sept 2026 at 18:18, Jason Merrill wrote:
> While we're touching the comments, how about mentioning the C23 changes
> as well?

Good idea. Like so?

-- >8 --

The <stdalign.h> macros were removed from C23 and C++26 but this patch
just tweaks the comment, without actually removing them. Doing so would
technically be a breaking change, but it's not expected that these
macros are widely used.

gcc/ChangeLog:

	* ginclude/stdalign.h (__alignas_is_defined, __alignof_is_defined):
	Note that the macros were removed in C23 and C++26.
	* ginclude/stdbool.h (__bool_true_false_are_defined): Note that
	the macro is obsolescent since C23 and deprecated since C++23.
---
 gcc/ginclude/stdalign.h | 3 ++-
 gcc/ginclude/stdbool.h  | 2 ++
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/gcc/ginclude/stdalign.h b/gcc/ginclude/stdalign.h
index a68cb28059ce..fdf016ef3bfe 100644
--- a/gcc/ginclude/stdalign.h
+++ b/gcc/ginclude/stdalign.h
@@ -33,7 +33,8 @@ see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
 #define alignof _Alignof
 #endif
 
-/* These are defined for C++, but deprecated in C++23.  */
+/* Added in C99, removed in C23.
+   Also defined in C++ since C++11, deprecated in C++23 and gone in C++26.  */
 #define __alignas_is_defined 1
 #define __alignof_is_defined 1
 
diff --git a/gcc/ginclude/stdbool.h b/gcc/ginclude/stdbool.h
index 9070a1876233..a45bd9b7712b 100644
--- a/gcc/ginclude/stdbool.h
+++ b/gcc/ginclude/stdbool.h
@@ -46,6 +46,8 @@ see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
 #endif /* __cplusplus */
 
 /* Signal that all the definitions are present.  */
+/* Added in C99, made obsolescent in C23.
+   Also defined in C++ since C++11, but deprecated in C++23.  */
 #define __bool_true_false_are_defined	1
 
 #endif	/* stdbool.h */
-- 
2.55.0