[PATCH] compat/posix.h: enable UNUSED warning messages for Clang

[PATCH] compat/posix.h: enable UNUSED warning messages for Clang

[Dominik Loidolt]

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(-)

diff --git a/compat/posix.h b/compat/posix.h
index 245386fa4a..ed83a4d9d4 100644
--- a/compat/posix.h
+++ b/compat/posix.h
@@ -35,7 +35,7 @@
  * When a parameter may be used or unused, depending on conditional
  * compilation, consider using MAYBE_UNUSED instead.
  */
-#if GIT_GNUC_PREREQ(4, 5)
+#if GIT_GNUC_PREREQ(4, 5) || defined(__clang__)
 #define UNUSED __attribute__((unused)) \
 	__attribute__((deprecated ("parameter declared as UNUSED")))
 #elif defined(__GNUC__)

base-commit: 67ad42147a7acc2af6074753ebd03d904476118f
--
2.54.0

Re: [PATCH] compat/posix.h: enable UNUSED warning messages for Clang

[Junio C Hamano]

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

> 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.

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.

> 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(-)
>
> diff --git a/compat/posix.h b/compat/posix.h
> index 245386fa4a..ed83a4d9d4 100644
> --- a/compat/posix.h
> +++ b/compat/posix.h
> @@ -35,7 +35,7 @@
>   * When a parameter may be used or unused, depending on conditional
>   * compilation, consider using MAYBE_UNUSED instead.
>   */
> -#if GIT_GNUC_PREREQ(4, 5)
> +#if GIT_GNUC_PREREQ(4, 5) || defined(__clang__)
>  #define UNUSED __attribute__((unused)) \
>  	__attribute__((deprecated ("parameter declared as UNUSED")))
>  #elif defined(__GNUC__)
>
> base-commit: 67ad42147a7acc2af6074753ebd03d904476118f
> --
> 2.54.0

Re: [PATCH] compat/posix.h: enable UNUSED warning messages for Clang

[Junio C Hamano]

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

>> I am not familiar with git's minimum compiler version but this patch
>> drops support for Clang < 2.9 from 2011.
>
> 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.

IOW, something like this, perhaps?

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

diff --git c/compat/posix.h w/compat/posix.h
index faaae1b655..0dd0637fc9 100644
--- c/compat/posix.h
+++ w/compat/posix.h
@@ -22,6 +22,17 @@
  #define GIT_GNUC_PREREQ(maj, min) 0
 #endif
 
+/*
+ * Similar for clang 
+ */
+#if defined(__clang__) && defined(__clang_minor__) && defined(__clang_major__)
+# define GIT_CLANG_PREREQ(maj, min) \
+	((__clang_major__ > (maj)) || \
+	 (__clang_major__ == (maj) && (__clang_minor__ >= (min))))
+#else
+# define GIT_CLANG_PREREQ(maj, min) 0
+#endif
+
 /*
  * UNUSED marks a function parameter that is always unused.  It also
  * can be used to annotate a function, a variable, or a type that is
@@ -35,7 +46,7 @@
  * When a parameter may be used or unused, depending on conditional
  * compilation, consider using MAYBE_UNUSED instead.
  */
-#if GIT_GNUC_PREREQ(4, 5)
+#if GIT_GNUC_PREREQ(4, 5) || GIT_CLANG_PREREQ(2, 9)
 #define UNUSED __attribute__((unused)) \
 	__attribute__((deprecated ("parameter declared as UNUSED")))
 #elif defined(__GNUC__)