trace2: NULL is not allowed for va_list

Some compilers don't allow NULL to be passed for a va_list,
and e.g. "gcc (Raspbian 6.3.0-18+rpi1+deb9u1) 6.3.0 20170516"
errors out like this:
 trace2/tr2_tgt_event.c:193:18:
   error: invalid operands to binary &&
   (have ‘int’ and ‘va_list {aka __va_list}’)
    if (fmt && *fmt && ap) {
                       ^^
I couldn't find any hints that va_list and pointers can be mixed,
and no hints that they can't either. Morten Welinder comments:

"C99, Section 7.15, simply says that va_list "is an object type suitable for
holding information needed by the macros va_start, va_end, and
va_copy". So clearly not guaranteed to be mixable with pointers...

The portable solution is to use "va_list" everywhere in the callchain.
As a consequence, both trace2_region_enter_fl() and trace2_region_leave_fl()
now take a variable argument list.
Signed-off-by: NTorsten Bögershausen <tboegi@web.de>
Acked-by: NJeff Hostetler <jeffhost@microsoft.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

trace2.c

@@ -548,10 +548,14 @@ void trace2_region_enter_printf_va_fl(const char *file, int line,
 }
 
 void trace2_region_enter_fl(const char *file, int line, const char *category,
-			    const char *label, const struct repository *repo)
+			    const char *label, const struct repository *repo, ...)
 {
+	va_list ap;
+	va_start(ap, repo);
 	trace2_region_enter_printf_va_fl(file, line, category, label, repo,
-					 NULL, NULL);
+					 NULL, ap);
+	va_end(ap);
+
 }
 
 void trace2_region_enter_printf_fl(const char *file, int line,
@@ -621,10 +625,13 @@ void trace2_region_leave_printf_va_fl(const char *file, int line,
 }
 
 void trace2_region_leave_fl(const char *file, int line, const char *category,
-			    const char *label, const struct repository *repo)
+			    const char *label, const struct repository *repo, ...)
 {
+	va_list ap;
+	va_start(ap, repo);
 	trace2_region_leave_printf_va_fl(file, line, category, label, repo,
-					 NULL, NULL);
+					 NULL, ap);
+	va_end(ap);
 }
 
 void trace2_region_leave_printf_fl(const char *file, int line,

trace2.h

@@ -238,7 +238,7 @@ void trace2_def_repo_fl(const char *file, int line, struct repository *repo);
  * on this thread.
  */
 void trace2_region_enter_fl(const char *file, int line, const char *category,
-			    const char *label, const struct repository *repo);
+			    const char *label, const struct repository *repo, ...);
 
 #define trace2_region_enter(category, label, repo) \
 	trace2_region_enter_fl(__FILE__, __LINE__, (category), (label), (repo))
@@ -278,7 +278,7 @@ void trace2_region_enter_printf(const char *category, const char *label,
  * in this nesting level.
  */
 void trace2_region_leave_fl(const char *file, int line, const char *category,
-			    const char *label, const struct repository *repo);
+			    const char *label, const struct repository *repo, ...);
 
 #define trace2_region_leave(category, label, repo) \
 	trace2_region_leave_fl(__FILE__, __LINE__, (category), (label), (repo))

trace2/tr2_tgt_event.c

@@ -190,7 +190,7 @@ static void fn_atexit(uint64_t us_elapsed_absolute, int code)
 static void maybe_add_string_va(struct json_writer *jw, const char *field_name,
 				const char *fmt, va_list ap)
 {
-	if (fmt && *fmt && ap) {
+	if (fmt && *fmt) {
 		va_list copy_ap;
 		struct strbuf buf = STRBUF_INIT;
 

trace2/tr2_tgt_normal.c

@@ -126,7 +126,7 @@ static void fn_atexit(uint64_t us_elapsed_absolute, int code)
 static void maybe_append_string_va(struct strbuf *buf, const char *fmt,
 				   va_list ap)
 {
-	if (fmt && *fmt && ap) {
+	if (fmt && *fmt) {
 		va_list copy_ap;
 
 		va_copy(copy_ap, ap);

trace2/tr2_tgt_perf.c

@@ -211,7 +211,7 @@ static void fn_atexit(uint64_t us_elapsed_absolute, int code)
 static void maybe_append_string_va(struct strbuf *buf, const char *fmt,
 				   va_list ap)
 {
-	if (fmt && *fmt && ap) {
+	if (fmt && *fmt) {
 		va_list copy_ap;
 
 		va_copy(copy_ap, ap);