Simplify by using attribute.h macros

attribute.h is partly designed for C2X forward compatibility,
since C2X will add some standard attributes.  Using its macros
should help insulate Emacs from C2X teething problems.
* src/conf_post.h: Include attribute.h.
(HAS_ATTRIBUTE, HAS_FEATURE): Rename from __has_attribute and
__has_feature, to avoid polluting the builtin namespace.
All uses changed.
(ATTRIBUTE_COLD, ATTRIBUTE_FORMAT, FALLTHROUGH, ATTRIBUTE_CONST)
(ATTRIBUTE_PURE, ATTRIBUTE_UNUSED, ATTRIBUTE_MAY_ALIAS)
(ATTRIBUTE_MALLOC, ATTRIBUTE_ALLOC_SIZE)
(ATTRIBUTE_RETURNS_NONNULL): Remove, as attribute.h does this now.
(NO_INLINE, EXTERNALLY_VISIBLE, ARG_NONNULL, ATTRIBUTE_UNUSED):
Simplify by defining in terms of attribute.h macros.
* src/systhread.h (ATTRIBUTE_WARN_UNUSED_RESULT): Remove.
All uses replaced by attribute.h’s NODISCARD.

2 files changed, 28 insertions, 84 deletions

diff --git a/src/conf_post.h b/src/conf_post.h
index 8a6b32998d8..953b783ebea 100644
--- a/src/conf_post.h
+++ b/src/conf_post.h
@@ -30,13 +30,15 @@ along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.  */
 #endif
 
 /* To help make dependencies clearer elsewhere, this file typically
-   does not #include other files.  The exceptions are first stdbool.h
+   does not #include other files.  The exceptions are stdbool.h
    because it is unlikely to interfere with configuration and bool is
-   such a core part of the C language, and second ms-w32.h (DOS_NT
+   such a core part of the C language, attribute.h because its
+   ATTRIBUTE_* macros are used here, and ms-w32.h (DOS_NT
    only) because it historically was included here and changing that
    would take some work.  */
 
 #include <stdbool.h>
+#include <attribute.h>
 
 #if defined WINDOWSNT && !defined DEFER_MS_W32_H
 # include <ms-w32.h>
@@ -65,31 +67,30 @@ typedef unsigned int bool_bf;
 typedef bool bool_bf;
 #endif
 
-/* Simulate __has_attribute on compilers that lack it.  It is used only
-   on arguments like alloc_size that are handled in this simulation.
-   __has_attribute should be used only in #if expressions, as Oracle
+/* A substitute for __has_attribute on compilers that lack it.
+   It is used only on arguments like cleanup that are handled here.
+   This macro should be used only in #if expressions, as Oracle
    Studio 12.5's __has_attribute does not work in plain code.  */
-#ifndef __has_attribute
-# define __has_attribute(a) __has_attribute_##a
-# define __has_attribute_alloc_size GNUC_PREREQ (4, 3, 0)
-# define __has_attribute_cleanup GNUC_PREREQ (3, 4, 0)
-# define __has_attribute_cold GNUC_PREREQ (4, 3, 0)
-# define __has_attribute_externally_visible GNUC_PREREQ (4, 1, 0)
-# define __has_attribute_no_address_safety_analysis false
-# define __has_attribute_no_sanitize_address GNUC_PREREQ (4, 8, 0)
-# define __has_attribute_no_sanitize_undefined GNUC_PREREQ (4, 9, 0)
-# define __has_attribute_returns_nonnull GNUC_PREREQ (4, 9, 0)
-# define __has_attribute_warn_unused_result GNUC_PREREQ (3, 4, 0)
+#ifdef __has_attribute
+# define HAS_ATTRIBUTE(a) __has_attribute (__##a##__)
+#else
+# define HAS_ATTRIBUTE(a) HAS_ATTR_##a
+# define HAS_ATTR_cleanup GNUC_PREREQ (3, 4, 0)
+# define HAS_ATTR_no_address_safety_analysis false
+# define HAS_ATTR_no_sanitize_address GNUC_PREREQ (4, 8, 0)
+# define HAS_ATTR_no_sanitize_undefined GNUC_PREREQ (4, 9, 0)
 #endif
 
-/* Simulate __has_feature on compilers that lack it.  It is used only
+/* A substitute for __has_feature on compilers that lack it.  It is used only
    to define ADDRESS_SANITIZER below.  */
-#ifndef __has_feature
-# define __has_feature(a) false
+#ifdef __has_feature
+# define HAS_FEATURE(a) __has_feature (a)
+#else
+# define HAS_FEATURE(a) false
 #endif
 
 /* True if addresses are being sanitized.  */
-#if defined __SANITIZE_ADDRESS__ || __has_feature (address_sanitizer)
+#if defined __SANITIZE_ADDRESS__ || HAS_FEATURE (address_sanitizer)
 # define ADDRESS_SANITIZER true
 #else
 # define ADDRESS_SANITIZER false
@@ -226,37 +227,8 @@ extern void _DebPrint (const char *fmt, ...);
 extern char *emacs_getenv_TZ (void);
 extern int emacs_setenv_TZ (char const *);
 
-/* Avoid __attribute__ ((cold)) on MinGW; see thread starting at
-   <https://lists.gnu.org/r/emacs-devel/2019-04/msg01152.html>. */
-#if __has_attribute (cold) && !defined __MINGW32__
-# define ATTRIBUTE_COLD __attribute__ ((cold))
-#else
-# define ATTRIBUTE_COLD
-#endif
-
-#if __GNUC__ >= 3  /* On GCC 3.0 we might get a warning.  */
-#define NO_INLINE __attribute__((noinline))
-#else
-#define NO_INLINE
-#endif
-
-#if __has_attribute (externally_visible)
-#define EXTERNALLY_VISIBLE __attribute__((externally_visible))
-#else
-#define EXTERNALLY_VISIBLE
-#endif
-
-#if GNUC_PREREQ (2, 7, 0)
-# define ATTRIBUTE_FORMAT(spec) __attribute__ ((__format__ spec))
-#else
-# define ATTRIBUTE_FORMAT(spec) /* empty */
-#endif
-
-#if GNUC_PREREQ (7, 0, 0)
-# define FALLTHROUGH __attribute__ ((__fallthrough__))
-#else
-# define FALLTHROUGH ((void) 0)
-#endif
+#define NO_INLINE ATTRIBUTE_NOINLINE
+#define EXTERNALLY_VISIBLE ATTRIBUTE_EXTERNALLY_VISIBLE
 
 #if GNUC_PREREQ (4, 4, 0) && defined __GLIBC_MINOR__
 # define PRINTF_ARCHETYPE __gnu_printf__
@@ -288,16 +260,8 @@ extern int emacs_setenv_TZ (char const *);
 #define ATTRIBUTE_FORMAT_PRINTF(string_index, first_to_check) \
   ATTRIBUTE_FORMAT ((PRINTF_ARCHETYPE, string_index, first_to_check))
 
-#define ARG_NONNULL _GL_ARG_NONNULL
-#define ATTRIBUTE_CONST _GL_ATTRIBUTE_CONST
-#define ATTRIBUTE_PURE _GL_ATTRIBUTE_PURE
-#define ATTRIBUTE_UNUSED _GL_UNUSED
-
-#if GNUC_PREREQ (3, 3, 0) && !defined __ICC
-# define ATTRIBUTE_MAY_ALIAS __attribute__ ((__may_alias__))
-#else
-# define ATTRIBUTE_MAY_ALIAS
-#endif
+#define ARG_NONNULL ATTRIBUTE_NONNULL
+#define ATTRIBUTE_UNUSED MAYBE_UNUSED
 
 /* Declare NAME to be a pointer to an object of type TYPE, initialized
    to the address ADDR, which may be of a different type.  Accesses
@@ -308,27 +272,13 @@ extern int emacs_setenv_TZ (char const *);
   type ATTRIBUTE_MAY_ALIAS *name = (type *) (addr)
 
 #if 3 <= __GNUC__
-# define ATTRIBUTE_MALLOC __attribute__ ((__malloc__))
 # define ATTRIBUTE_SECTION(name) __attribute__((section (name)))
 #else
-# define ATTRIBUTE_MALLOC
 #define ATTRIBUTE_SECTION(name)
 #endif
 
-#if __has_attribute (alloc_size)
-# define ATTRIBUTE_ALLOC_SIZE(args) __attribute__ ((__alloc_size__ args))
-#else
-# define ATTRIBUTE_ALLOC_SIZE(args)
-#endif
-
 #define ATTRIBUTE_MALLOC_SIZE(args) ATTRIBUTE_MALLOC ATTRIBUTE_ALLOC_SIZE (args)
 
-#if __has_attribute (returns_nonnull)
-# define ATTRIBUTE_RETURNS_NONNULL __attribute__ ((returns_nonnull))
-#else
-# define ATTRIBUTE_RETURNS_NONNULL
-#endif
-
 /* Work around GCC bug 59600: when a function is inlined, the inlined
    code may have its addresses sanitized even if the function has the
    no_sanitize_address attribute.  This bug is fixed in GCC 4.9.0 and
diff --git a/src/systhread.h b/src/systhread.h
index 005388fd5a4..73c764a9401 100644
--- a/src/systhread.h
+++ b/src/systhread.h
@@ -21,12 +21,6 @@ along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.  */
 
 #include <stdbool.h>
 
-#if __has_attribute (warn_unused_result)
-# define ATTRIBUTE_WARN_UNUSED_RESULT __attribute__ ((warn_unused_result))
-#else
-# define ATTRIBUTE_WARN_UNUSED_RESULT
-#endif
-
 #ifdef THREADS_ENABLED
 
 #ifdef HAVE_PTHREAD
@@ -108,13 +102,13 @@ extern void sys_cond_broadcast (sys_cond_t *);
 extern void sys_cond_destroy (sys_cond_t *);
 
 extern sys_thread_t sys_thread_self (void)
-  ATTRIBUTE_WARN_UNUSED_RESULT;
+  NODISCARD;
 extern bool sys_thread_equal (sys_thread_t, sys_thread_t)
-  ATTRIBUTE_WARN_UNUSED_RESULT;
+  NODISCARD;
 
 extern bool sys_thread_create (sys_thread_t *, thread_creation_function *,
                                void *)
-  ATTRIBUTE_WARN_UNUSED_RESULT;
+  NODISCARD;
 
 extern void sys_thread_yield (void);
 extern void sys_thread_set_name (const char *);