[tz] [PROPOSED] Use C23 [[maybe_unused]] if available

[Paul Eggert]

* Makefile (GCC_DEBUG_FLAGS): Omit -Wno-unused-parameters, as the
code is now safe for gcc -Wunused-parameters.
* private.h (ATTRIBUTE_MAYBE_UNUSED): New macro.
* localtime.c (gmtsub):
* strftime.c (strftime_l) [HAVE_STRFTIME_L]:
* zdump.c (gmtoff):
Use it to mark possibly-unused parameters.
* zdump.c (hunt):
* zic.c (getleapdatetime):
Omit unused arg. All callers changed.
---
 Makefile    |  2 +-
 localtime.c |  4 ++--
 private.h   | 13 +++++++++++++
 strftime.c  |  2 +-
 zdump.c     | 13 +++++++------
 zic.c       |  6 +++---
 6 files changed, 27 insertions(+), 13 deletions(-)

diff --git a/Makefile b/Makefile
index 92d78cb4..b2c6ff6f 100644
--- a/Makefile
+++ b/Makefile
@@ -300,7 +300,7 @@ GCC_DEBUG_FLAGS = -DGCC_LINT -g3 -O3 -fno-common \
   -Wtrampolines -Wundef -Wuninitialized -Wunused-macros -Wuse-after-free=3 \
   -Wvariadic-macros -Wvla -Wwrite-strings \
   -Wno-address -Wno-format-nonliteral -Wno-sign-compare \
-  -Wno-type-limits -Wno-unused-parameter
+  -Wno-type-limits
 #
 # If your system has a "GMT offset" field in its "struct tm"s
 # (or if you decide to add such a field in your system's "time.h" file),
diff --git a/localtime.c b/localtime.c
index 7faa5d32..4dd9d259 100644
--- a/localtime.c
+++ b/localtime.c
@@ -1662,8 +1662,8 @@ localtime_r(const time_t *timep, struct tm *tmp)
 */
 
 static struct tm *
-gmtsub(struct state const *sp, time_t const *timep, int_fast32_t offset,
-       struct tm *tmp)
+gmtsub(ATTRIBUTE_MAYBE_UNUSED struct state const *sp, time_t const *timep,
+       int_fast32_t offset, struct tm *tmp)
 {
 	register struct tm *	result;
 
diff --git a/private.h b/private.h
index 4d40582e..fee18cb2 100644
--- a/private.h
+++ b/private.h
@@ -433,6 +433,19 @@ typedef unsigned long uintmax_t;
 # define ATTRIBUTE_FORMAT(spec) /* empty */
 #endif
 
+#ifdef __has_c_attribute
+# if __has_c_attribute(__maybe_unused__)
+#  define ATTRIBUTE_MAYBE_UNUSED [[__maybe_unused__]]
+# endif
+#endif
+#ifndef ATTRIBUTE_MAYBE_UNUSED
+# if 2 < __GNUC__ + (7 <= __GNUC_MINOR__)
+#  define ATTRIBUTE_MAYBE_UNUSED __attribute__ ((__unused__))
+# else
+#  define ATTRIBUTE_MAYBE_UNUSED /* empty */
+# endif
+#endif
+
 #if !defined _Noreturn && __STDC_VERSION__ < 201112
 # if 2 < __GNUC__ + (8 <= __GNUC_MINOR__)
 #  define _Noreturn __attribute__((__noreturn__))
diff --git a/strftime.c b/strftime.c
index 9ea40fec..b23b6101 100644
--- a/strftime.c
+++ b/strftime.c
@@ -117,7 +117,7 @@ static char *	_yconv(int, int, bool, bool, char *, char const *);
 #if HAVE_STRFTIME_L
 size_t
 strftime_l(char *s, size_t maxsize, char const *format, struct tm const *t,
-	   locale_t locale)
+	   ATTRIBUTE_MAYBE_UNUSED locale_t locale)
 {
   /* Just call strftime, as only the C locale is supported.  */
   return strftime(s, maxsize, format, t);
diff --git a/zdump.c b/zdump.c
index 89bcd25c..de1e1116 100644
--- a/zdump.c
+++ b/zdump.c
@@ -91,7 +91,7 @@ static bool	errout;
 static char const *abbr(struct tm const *);
 static intmax_t	delta(struct tm *, struct tm *) ATTRIBUTE_PURE;
 static void dumptime(struct tm const *);
-static time_t hunt(timezone_t, char *, time_t, time_t, bool);
+static time_t hunt(timezone_t, time_t, time_t, bool);
 static void show(timezone_t, char *, time_t, bool);
 static void showextrema(timezone_t, char *, time_t, struct tm *, time_t);
 static void showtrans(char const *, struct tm const *, time_t, char const *,
@@ -627,7 +627,7 @@ main(int argc, char *argv[])
 		      || (ab && (delta(&newtm, &tm) != newt - t
 				 || newtm.tm_isdst != tm.tm_isdst
 				 || strcmp(abbr(&newtm), ab) != 0))) {
-		    newt = hunt(tz, argv[i], t, newt, false);
+		    newt = hunt(tz, t, newt, false);
 		    newtmp = localtime_rz(tz, &newt, &newtm);
 		    newtm_ok = newtmp != NULL;
 		    if (iflag)
@@ -707,7 +707,7 @@ yeartot(intmax_t y)
 	return t;
 }
 
-/* Search for a discontinuity in timezone TZ with name NAME, in the
+/* Search for a discontinuity in timezone TZ, in the
    timestamps ranging from LOT through HIT.  LOT and HIT disagree
    about some aspect of timezone.  If ONLY_OK, search only for
    definedness changes, i.e., localtime succeeds on one side of the
@@ -715,7 +715,7 @@ yeartot(intmax_t y)
    before the transition from LOT's settings.  */
 
 static time_t
-hunt(timezone_t tz, char *name, time_t lot, time_t hit, bool only_ok)
+hunt(timezone_t tz, time_t lot, time_t hit, bool only_ok)
 {
 	static char *		loab;
 	static ptrdiff_t	loabsize;
@@ -807,7 +807,8 @@ adjusted_yday(struct tm const *a, struct tm const *b)
    my_gmtime_r and use its result instead of B.  Otherwise, B is the
    possibly nonnull result of an earlier call to my_gmtime_r.  */
 static long
-gmtoff(struct tm const *a, time_t *t, struct tm const *b)
+gmtoff(struct tm const *a, ATTRIBUTE_MAYBE_UNUSED time_t *t,
+       ATTRIBUTE_MAYBE_UNUSED struct tm const *b)
 {
 #ifdef TM_GMTOFF
   return a->TM_GMTOFF;
@@ -878,7 +879,7 @@ static void
 showextrema(timezone_t tz, char *zone, time_t lo, struct tm *lotmp, time_t hi)
 {
   struct tm localtm[2], gmtm[2];
-  time_t t, boundary = hunt(tz, zone, lo, hi, true);
+  time_t t, boundary = hunt(tz, lo, hi, true);
   bool old = false;
   hi = (SECSPERDAY < hi - boundary
 	? boundary + SECSPERDAY
diff --git a/zic.c b/zic.c
index 8f8088ec..7a7a5094 100644
--- a/zic.c
+++ b/zic.c
@@ -1970,7 +1970,7 @@ inzsub(char **fields, int nfields, bool iscont)
 }
 
 static zic_t
-getleapdatetime(char **fields, int nfields, bool expire_line)
+getleapdatetime(char **fields, bool expire_line)
 {
 	register const char *		cp;
 	register const struct lookup *	lp;
@@ -2048,7 +2048,7 @@ inleap(char **fields, int nfields)
   if (nfields != LEAP_FIELDS)
     error(_("wrong number of fields on Leap line"));
   else {
-    zic_t t = getleapdatetime(fields, nfields, false);
+    zic_t t = getleapdatetime(fields, false);
     if (0 <= t) {
       struct lookup const *lp = byword(fields[LP_ROLL], leap_types);
       if (!lp)
@@ -2076,7 +2076,7 @@ inexpires(char **fields, int nfields)
   else if (0 <= leapexpires)
     error(_("multiple Expires lines"));
   else
-    leapexpires = getleapdatetime(fields, nfields, true);
+    leapexpires = getleapdatetime(fields, true);
 }
 
 static void
-- 
2.37.2