Treat Clang like GCC 4.5+ so using an UNUSED parameter emits the intended warning message.

Commit 7c07f36ad2 (git-compat-util.h: GCC deprecated message arg only in GCC 4.5+, 2022-10-05) restricted use of the deprecated attribute's message argument in the UNUSED macro to GCC 4.5 or newer.

Clang identifies itself as GNUC 4.2.1 for compatibility, causing the current check to use the deprecated attribute without a message, even though Clang supports deprecated("...") since version 2.9 (2011).

Signed-off-by: Dominik Loidolt <dominik.loidolt@univie.ac.at>
---
I am not familiar with git's minimum compiler version but this patch
drops support for Clang < 2.9 from 2011.

Dominik P.S. This is my first patch sent by email. Please let me know if I missed something.

 compat/posix.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Dominik Loidolt <dominik.loidolt@univie.ac.at> writes:

Does this "drop support" because you force _all_ versions of Clang to use the "deprecated" attribute, even though you _know_ some older versions do not understand it? Don't these versions identify themselves so that you can do

	#if defined(__clang__) && CLANG_VERSION >= 2.9

I do not know if the userbase of GCC and Clang upgrade with a similar cadence, or we seem to say that we care about GCC 4.5 (2010), so giving a similar version detection for Clang and exclude ones older than 2.9 sounds more appropriate.

Junio C Hamano <gitster@pobox.com> writes:

IOW, something like this, perhaps?

 compat/posix.h | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

On Mon, May 04, 2026 at 10:41:16AM +0900, Junio C Hamano wrote:

Yes, you're right. My original patch breaks older Clang versions for no good reason.

I'll send a v2 with an explicit Clang version check, as you suggested.

Thanks,
 Dominik

Use a dedicated Clang version check for the UNUSED macro.

Commit 7c07f36ad2 (git-compat-util.h: GCC deprecated message arg only in GCC 4.5+, 2022-10-05) restricted use of the deprecated attribute's message argument in the UNUSED macro to GCC 4.5 or newer.

Clang identifies itself as GNUC 4.2.1 for compatibility, so GIT_GNUC_PREREQ(4, 5) does not detect whether Clang supports the deprecated("...") form. Add GIT_CLANG_PREREQ() macro and use it to enable the UNUSED warning message for Clang 2.9 and newer.

Signed-off-by: Dominik Loidolt <dominik.loidolt@univie.ac.at>
---
v2:
 - add GIT_CLANG_PREREQ()
 - require Clang 2.9+ for deprecated("...") in UNUSED

 compat/posix.h | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

On Fri, Jun 05, 2026 at 11:46:47AM +0200, Dominik Loidolt wrote:

Ah. I was briefly wondering about this because the UNUSED macro already works. But the important part here is that it's really only about better diagnostics via the attribute message.

There's a second user of `GIT_GNUC_PREREQ` in "git-compat-util.h", but that user checks for GCC 3.1. And as Clang identifies as a newer version we don't have to adapt any other callsites.

Micronit, not worth rerolling over: this could have easily been a single line: `/* Similar for Clang. */`

Makes sense, thanks!

Patrick

Thanks for the review!

I noticed that the version-check style now differs between GCC and the newly introduced Clang checks, would it make sense to make them consistent? Like:

On Fri, Jun 05, 2026 at 01:50:29PM +0200, Dominik Loidolt wrote:

I was wondering about that, too. The question that I have is whether there's any particular reason why the check was written that way. So in the best case we'd do some digging into the history to figure out why this looks the way it looks like.

Patrick

On Fri, Jun 05, 2026 at 03:22:49PM +0200, Patrick Steinhardt wrote:

I think the current bit-shift style introduced by 89c855ed3c (git-compat-util.h: implement a different ARRAY_SIZE macro for for safely deriving the size of array, 2015-04-30) was inherited from glibc [0].

I found that NetBSD [1] has long used the more explicit comparison form instead of the bit-shift style, and other BSDs seem to do the same. So there is at least established precedent for writing the version check that way. :-)

I see no obvious reason to prefer the bit-shift style today.

 Dominik

[0] https://sourceware.org/git/?p=glibc.git;a=commitdiff;h=4360eafdd20769fa9d42c075853271debd06f7d1 [1] https://github.com/NetBSD/src/commit/2fffc76da21e012509677f5310464f62797bd1bf

On Fri, Jun 05, 2026 at 05:53:45PM +0200, Dominik Loidolt wrote:

Thanks for digging!

I don't really see a reason to keep the bitshift style, either. It could make a difference if it was ever evaluated at runtime, as we would evaluate the arguments multiple times with youur version. But all of the instances we have are evaluated at compile time anwyay, so that doesn't matter much to us.

I'll leave it up to you whether you want to send another iteration of this patch series that also adapts the preexisting callsite to use the new style.

Thanks!

Patrick

Use a dedicated Clang version check for the UNUSED macro.

Commit 7c07f36ad2 (git-compat-util.h: GCC deprecated message arg only in GCC 4.5+, 2022-10-05) restricted use of the deprecated attribute's message argument in the UNUSED macro to GCC 4.5 or newer.

Clang identifies itself as GNUC 4.2.1 for compatibility, so GIT_GNUC_PREREQ(4, 5) does not detect whether Clang supports the deprecated("...") form. Add GIT_CLANG_PREREQ() macro and use it to enable the UNUSED warning message for Clang 2.9 and newer.

Signed-off-by: Dominik Loidolt <dominik.loidolt@univie.ac.at>
---
v3:
- fix comment style nit
- remove unnecessary parentheses around __clang_minor__ >= (min)

 compat/posix.h | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

Replace the glibc-style bit-shift version comparison with an explicit major/minor comparison. This is easier to read and is consistent with the format already used by GIT_CLANG_PREREQ() and many BSD <sys/cdefs.h> headers.

This has no runtime impact, as the macro is evaluated at compile time. It is also more future-proof, as it no longer assumes that GCC version components stay below 65536.

Signed-off-by: Dominik Loidolt <dominik.loidolt@univie.ac.at>
---
 compat/posix.h | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

On Mon, Jun 08, 2026 at 02:44:19PM +0200, Dominik Loidolt wrote:

It's a bit funny to use `GIT_CLANG_PREREQ()` as an argument here as we've just added it in the preceding commit.

I feel like all the message needs to say is "let's do it for consistency, and it's easier to read". That would've been sufficient, whereas this argument here feels a bit thin.

Doesn't matter much though, and I think ultimately the message is fine as-is, even though the reasoning is a bit funny.

It would've been nice to either move these changes into a preparatory commit or at least mention them

The change itself makes sense to me.

I'm not sure myself whether this could use another reroll. It's all just nits, and the intent is clear enough.

Thanks!

Patrick

Thanks again for taking the time to review my contribution.

On Fri, Jun 12, 2026 at 03:27:36PM +0200, Patrick Steinhardt wrote:

Agreed. I'll simplify the commit message. The "future-proof" bit was a joke I just couldn't resist, but it may cause more confusion than it is worth. I'll drop it.

Agreed. I'll split the cleanup into a separate commit.

I think it's worth rerolling.

Thanks,
 Dominik

This series enables the intended UNUSED warning message with Clang by adding a dedicated Clang version check. It also cleans up the nearby GIT_GNUC_PREREQ() and UNUSED macros.

Changes since v3:
- split style-only cleanups into their own patch
- fix the UNUSED preprocessor indentation style
- simplify the GIT_GNUC_PREREQ() comparison commit message
- keep the Clang-specific note in the patch that adds GIT_CLANG_PREREQ()

Thanks,
 Dominik

Dominik Loidolt (3):
  compat/posix.h: enable UNUSED warning messages for Clang
  compat/posix.h: clean up GIT_GNUC_PREREQ() and UNUSED
  compat/posix.h: simplify GIT_GNUC_PREREQ() comparison

 compat/posix.h | 35 +++++++++++++++++++++++------------
 1 file changed, 23 insertions(+), 12 deletions(-)

Range-diff against v3:
1:  62f5bce297 ! 1:  9ec87cd815 compat/posix.h: enable UNUSED warning messages for Clang
    @@ Commit message
         Signed-off-by: Dominik Loidolt <dominik.loidolt@univie.ac.at>

      ## compat/posix.h ##
    +@@
    +  *   ... code requiring gcc 2.8 or later ...
    +  *  #endif
    +  *
    ++ * Note that Clang and other compilers define __GNUC__ for compatibility; use
    ++ * GIT_CLANG_PREREQ() to check for specific Clang versions.
    ++ *
    +  * This macro of course is not part of POSIX, but we need it for the UNUSED
    +  * macro which is used by some of our POSIX compatibility wrappers.
    + */
     @@
       #define GIT_GNUC_PREREQ(maj, min) 0
      #endif
2:  a8fe5047a4 ! 2:  1a695af9ca compat/posix.h: simplify GIT_GNUC_PREREQ() comparison
    @@ Metadata
     Author: Dominik Loidolt <dominik.loidolt@univie.ac.at>

      ## Commit message ##
    -    compat/posix.h: simplify GIT_GNUC_PREREQ() comparison
    +    compat/posix.h: clean up GIT_GNUC_PREREQ() and UNUSED

    -    Replace the glibc-style bit-shift version comparison with an explicit
    -    major/minor comparison. This is easier to read and is consistent with
    -    the format already used by GIT_CLANG_PREREQ() and many BSD
    -    <sys/cdefs.h> headers.
    +    Fix the preprocessor indentation of the GIT_GNUC_PREREQ() and UNUSED
    +    macros according to the CodingGuidelines, without changing their
    +    behavior.

    -    This has no runtime impact, as the macro is evaluated at compile time.
    -    It is also more future-proof, as it no longer assumes that GCC version
    -    components stay below 65536.
    +    Adjust the spelling in the GIT_GNUC_PREREQ() comment block.

         Signed-off-by: Dominik Loidolt <dominik.loidolt@univie.ac.at>

      ## compat/posix.h ##
     @@
    - #define _FILE_OFFSET_BITS 64

      /*
    -- * Derived from Linux "Features Test Macro" header
    +  * Derived from Linux "Features Test Macro" header
     - * Convenience macros to test the versions of gcc (or
     - * a compatible compiler).
     + * Convenience macros to test the versions of GCC (or a compatible compiler).
    @@ compat/posix.h
     + *   ... code requiring GCC 2.8 or later ...
       *  #endif
       *
    -+ * Note that Clang and other compilers define __GNUC__ for compatibility; use
    -+ * GIT_CLANG_PREREQ() to check for specific Clang versions.
    -+ *
    +  * Note that Clang and other compilers define __GNUC__ for compatibility; use
    +@@
    +  *
       * This macro of course is not part of POSIX, but we need it for the UNUSED
       * macro which is used by some of our POSIX compatibility wrappers.
     -*/
     + */
      #if defined(__GNUC__) && defined(__GNUC_MINOR__)
      # define GIT_GNUC_PREREQ(maj, min) \
    --	((__GNUC__ << 16) + __GNUC_MINOR__ >= ((maj) << 16) + (min))
    -+	((__GNUC__ > (maj)) || \
    -+	 (__GNUC__ == (maj) && __GNUC_MINOR__ >= (min)))
    + 	((__GNUC__ << 16) + __GNUC_MINOR__ >= ((maj) << 16) + (min))
      #else
     - #define GIT_GNUC_PREREQ(maj, min) 0
     +# define GIT_GNUC_PREREQ(maj, min) 0
      #endif

      /* Similar for Clang. */
    +@@
    +  * compilation, consider using MAYBE_UNUSED instead.
    +  */
    + #if GIT_GNUC_PREREQ(4, 5) || GIT_CLANG_PREREQ(2, 9)
    +-#define UNUSED __attribute__((unused)) \
    +-	__attribute__((deprecated ("parameter declared as UNUSED")))
    ++# define UNUSED __attribute__((unused)) \
    ++	__attribute__((deprecated("parameter declared as UNUSED")))
    + #elif defined(__GNUC__)
    +-#define UNUSED __attribute__((unused)) \
    ++# define UNUSED __attribute__((unused)) \
    + 	__attribute__((deprecated))
    + #else
    +-#define UNUSED
    ++# define UNUSED
    + #endif
    +
    + #ifdef __MINGW64__
-:  ---------- > 3:  289b7d9f8e compat/posix.h: simplify GIT_GNUC_PREREQ() comparison

base-commit: a89346e34a937f001e5d397ee62224e3e9852040 -- 2.54.0

Fix the preprocessor indentation of the GIT_GNUC_PREREQ() and UNUSED macros according to the CodingGuidelines, without changing their behavior.

Adjust the spelling in the GIT_GNUC_PREREQ() comment block.

Signed-off-by: Dominik Loidolt <dominik.loidolt@univie.ac.at>
---
 compat/posix.h | 17 ++++++++---------
 1 file changed, 8 insertions(+), 9 deletions(-)

Use a dedicated Clang version check for the UNUSED macro.

Commit 7c07f36ad2 (git-compat-util.h: GCC deprecated message arg only in GCC 4.5+, 2022-10-05) restricted use of the deprecated attribute's message argument in the UNUSED macro to GCC 4.5 or newer.

Clang identifies itself as GNUC 4.2.1 for compatibility, so GIT_GNUC_PREREQ(4, 5) does not detect whether Clang supports the deprecated("...") form. Add GIT_CLANG_PREREQ() macro and use it to enable the UNUSED warning message for Clang 2.9 and newer.

Signed-off-by: Dominik Loidolt <dominik.loidolt@univie.ac.at>
---
 compat/posix.h | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

GIT_GNUC_PREREQ() uses a glibc-style bit-shift version comparison, which is harder to read than an explicit major/minor comparison.

Use an explicit comparison, as in many BSD <sys/cdefs.h> headers, and drop the Linux header attribution comment because it no longer applies.

Signed-off-by: Dominik Loidolt <dominik.loidolt@univie.ac.at>
---
 compat/posix.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

Dominik Loidolt <dominik.loidolt@univie.ac.at> writes:

Looking good and all the points Patrick raised during the review of the previous round seem to have been addressed nicely.

Will replace.  Shall we mark it for 'next' now?

Thanks.

On Sat, Jun 13, 2026 at 09:39:03AM -0700, Junio C Hamano wrote:

Yeah, I'm happy with this version. Thanks!

Patrick