[3/4] Add utility macros for clang detection, and deprecation with messages.
Commit Message
Add three new macros to features.h and sys/cdefs.h:
* __glibc_clang_prereq: just like __GNUC_PREREQ, but for clang.
* __glibc_clang_has_extension: wraps clang's intrinsic __has_extension.
Writing "#if defined __clang__ && __has_extension (...)" doesn't work,
because compilers other than clang will object to the unknown macro
__has_extension even though they don't need to evaluate it.
Instead, write "#if __glibc_clang_has_extension (...)".
* __attribute_deprecated_msg__(msg): like __attribute_deprecated__, but
if possible, prints a message.
The first two are used to define the third. The third will be used
in patch #4.
ChangeLog:
* include/features.h (__glibc_clang_prereq): New macro.
* misc/sys/cdefs.h (__glibc_clang_has_extension)
(__attribute_deprecated_msg__): New macros.
---
include/features.h | 19 +++++++++++++++----
misc/sys/cdefs.h | 22 +++++++++++++++++++++-
2 files changed, 36 insertions(+), 5 deletions(-)
Comments
On Fri, May 13, 2016 at 9:26 AM, Zack Weinberg <zackw@panix.com> wrote:
> Add three new macros to features.h and sys/cdefs.h:
>
> * __glibc_clang_prereq: just like __GNUC_PREREQ, but for clang.
> * __glibc_clang_has_extension: wraps clang's intrinsic __has_extension.
> Writing "#if defined __clang__ && __has_extension (...)" doesn't work,
> because compilers other than clang will object to the unknown macro
> __has_extension even though they don't need to evaluate it.
> Instead, write "#if __glibc_clang_has_extension (...)".
>
> * __attribute_deprecated_msg__(msg): like __attribute_deprecated__, but
> if possible, prints a message.
Ping?
@@ -125,13 +125,13 @@
# define __KERNEL_STRICT_NAMES
#endif
-/* Convenience macros to test the versions of glibc and gcc.
- Use them like this:
+/* Convenience macro to test the version of gcc.
+ Use like this:
#if __GNUC_PREREQ (2,8)
... code requiring gcc 2.8 or later ...
#endif
- Note - they won't work for gcc1 or glibc1, since the _MINOR macros
- were not defined then. */
+ Note: only works for GCC 2.0 and later, because __GNUC_MINOR__ was
+ added in 2.0. */
#if defined __GNUC__ && defined __GNUC_MINOR__
# define __GNUC_PREREQ(maj, min) \
((__GNUC__ << 16) + __GNUC_MINOR__ >= ((maj) << 16) + (min))
@@ -139,6 +139,17 @@
# define __GNUC_PREREQ(maj, min) 0
#endif
+/* Similarly for clang. Features added to GCC after version 4.2 may
+ or may not also be available in clang, and their definitions of
+ __GNUC(_MINOR)__ are fixed at 4 and 2 respectively. Not all such
+ features can be queried via __has_extension/__has_feature. */
+#if defined __clang_major__ && defined __clang_minor__
+# define __glibc_clang_prereq(maj, min) \
+ ((__clang_major__ << 16) + __clang_minor__ >= ((maj) << 16) + (min))
+#else
+# define __glibc_clang_prereq(maj, min) 0
+#endif
+
/* _BSD_SOURCE and _SVID_SOURCE are deprecated aliases for
_DEFAULT_SOURCE. If _DEFAULT_SOURCE is present we do not
issue a warning; the expectation is that the source is being
@@ -77,6 +77,15 @@
#endif /* GCC. */
+/* Compilers that are not clang may object to
+ #if defined __clang__ && __has_extension(...)
+ even though they do not need to evaluate the right-hand side of the &&. */
+#if defined __clang__ && defined __has_extension
+# define __glibc_clang_has_extension(ext) __has_extension (ext)
+#else
+# define __glibc_clang_has_extension(ext) 0
+#endif
+
/* These two macros are not used in glibc anymore. They are kept here
only because some other projects expect the macros to be defined. */
#define __P(args) args
@@ -249,13 +258,24 @@
# define __attribute_noinline__ /* Ignore */
#endif
-/* gcc allows marking deprecated functions. */
+/* Since version 3.2, gcc allows marking deprecated functions. */
#if __GNUC_PREREQ (3,2)
# define __attribute_deprecated__ __attribute__ ((__deprecated__))
#else
# define __attribute_deprecated__ /* Ignore */
#endif
+/* Since version 4.5, gcc also allows one to specify the message printed
+ when a deprecated function is used. clang claims to be gcc 4.2, but
+ may also support this feature. */
+#if __GNUC_PREREQ (4,5) || \
+ __glibc_clang_has_extension (__attribute_deprecated_with_message__)
+# define __attribute_deprecated_msg__(msg) \
+ __attribute__ ((__deprecated__ (msg)))
+#else
+# define __attribute_deprecated_msg__(msg) __attribute_deprecated__
+#endif
+
/* At some point during the gcc 2.8 development the `format_arg' attribute
for functions was introduced. We don't want to use it unconditionally
(although this would be possible) since it generates warnings.