Add the LAST_ARG_MUST_BE_NULL macro

The sentinel function attribute is not understood by versions of
the gcc compiler prior to v4.0. At present, for earlier versions
of gcc, the build issues 108 warnings related to the unknown
attribute. In order to suppress the warnings, we conditionally
define the LAST_ARG_MUST_BE_NULL macro to provide the sentinel attribute
for gcc v4.0 and newer.

Signed-off-by: Ramsay Jones <ramsay@ramsay1.demon.co.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

argv-array.h

@@ -15,7 +15,7 @@ void argv_array_init(struct argv_array *);
 void argv_array_push(struct argv_array *, const char *);
 __attribute__((format (printf,2,3)))
 void argv_array_pushf(struct argv_array *, const char *fmt, ...);
-__attribute__((sentinel))
+LAST_ARG_MUST_BE_NULL
 void argv_array_pushl(struct argv_array *, ...);
 void argv_array_pop(struct argv_array *);
 void argv_array_clear(struct argv_array *);

builtin/revert.c

@@ -54,7 +54,7 @@ static int option_parse_x(const struct option *opt,
 	return 0;
 }
 
-__attribute__((sentinel))
+LAST_ARG_MUST_BE_NULL
 static void verify_opt_compatible(const char *me, const char *base_opt, ...)
 {
 	const char *this_opt;
@@ -71,7 +71,7 @@ static void verify_opt_compatible(const char *me, const char *base_opt, ...)
 		die(_("%s: %s cannot be used with %s"), me, this_opt, base_opt);
 }
 
-__attribute__((sentinel))
+LAST_ARG_MUST_BE_NULL
 static void verify_opt_mutually_compatible(const char *me, ...)
 {
 	const char *opt1, *opt2 = NULL;

exec_cmd.h

@@ -7,7 +7,7 @@ extern const char *git_exec_path(void);
 extern void setup_path(void);
 extern const char **prepare_git_cmd(const char **argv);
 extern int execv_git_cmd(const char **argv); /* NULL terminated */
-__attribute__((sentinel))
+LAST_ARG_MUST_BE_NULL
 extern int execl_git_cmd(const char *cmd, ...);
 extern const char *system_path(const char *path);
 

git-compat-util.h

@@ -295,6 +295,13 @@ extern char *gitbasename(char *);
 #endif
 #endif
 
+/* The sentinel attribute is valid from gcc version 4.0 */
+#if defined(__GNUC__) && (__GNUC__ >= 4)
+#define LAST_ARG_MUST_BE_NULL __attribute__((sentinel))
+#else
+#define LAST_ARG_MUST_BE_NULL
+#endif
+
 #include "compat/bswap.h"
 
 #ifdef USE_WILDMATCH

run-command.h

@@ -46,7 +46,7 @@ int finish_command(struct child_process *);
 int run_command(struct child_process *);
 
 extern char *find_hook(const char *name);
-__attribute__((sentinel))
+LAST_ARG_MUST_BE_NULL
 extern int run_hook(const char *index_file, const char *name, ...);
 
 #define RUN_COMMAND_NO_STDIN 1