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

[Junio C Hamano <gitster@pobox.com>]

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__)