[PATCH -v2] strbuf: change an always NULL/"" strbuf_addftime() param to bool

["Ævar Arnfjörð Bjarmason" <avarab@gmail.com>]

Change the code for deciding what's to be done about %Z to stop
passing always either a NULL or "" char * to
strbuf_addftime(). Instead pass a boolean int to indicate whether the
strftime() %Z format should be expanded to an empty string, which is
what this code is actually doing.

This code grew organically between the changes in 9eafe86d58 ("Merge
branch 'rs/strbuf-addftime-zZ'", 2017-06-22) yielding an end result
that wasn't very readable.

Out of context it looked as though the call to strbuf_addstr() might
be adding a custom tz_name to the string, but actually tz_name would
always be "", so the call to strbuf_addstr() just to add an empty
string to the format was pointless.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
---

I believe this addresses the comments in the thread so far. Also Re:
René's "why const?" in a2673ce4-5cf8-6b40-d4db-8e2a49518138@web.de:
Because tzname_from_tz isn't changed in the body of the function, only
read.

 date.c   | 2 +-
 strbuf.c | 5 ++---
 strbuf.h | 5 +++--
 3 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/date.c b/date.c
index 1fd6d66375..17db07d905 100644
--- a/date.c
+++ b/date.c
@@ -256,7 +256,7 @@ const char *show_date(timestamp_t time, int tz, const struct date_mode *mode)
 			tm->tm_hour, tm->tm_min, tm->tm_sec, tz);
 	else if (mode->type == DATE_STRFTIME)
 		strbuf_addftime(&timebuf, mode->strftime_fmt, tm, tz,
-				mode->local ? NULL : "");
+				mode->local);
 	else
 		strbuf_addf(&timebuf, "%.3s %.3s %d %02d:%02d:%02d %d%c%+05d",
 				weekday_names[tm->tm_wday],
diff --git a/strbuf.c b/strbuf.c
index be3b9e37b1..92b7bda772 100644
--- a/strbuf.c
+++ b/strbuf.c
@@ -786,7 +786,7 @@ char *xstrfmt(const char *fmt, ...)
 }
 
 void strbuf_addftime(struct strbuf *sb, const char *fmt, const struct tm *tm,
-		     int tz_offset, const char *tz_name)
+		     int tz_offset, const int tzname_from_tz)
 {
 	struct strbuf munged_fmt = STRBUF_INIT;
 	size_t hint = 128;
@@ -815,8 +815,7 @@ void strbuf_addftime(struct strbuf *sb, const char *fmt, const struct tm *tm,
 			fmt++;
 			break;
 		case 'Z':
-			if (tz_name) {
-				strbuf_addstr(&munged_fmt, tz_name);
+			if (!tzname_from_tz) {
 				fmt++;
 				break;
 			}
diff --git a/strbuf.h b/strbuf.h
index 4559035c47..eba5d59a77 100644
--- a/strbuf.h
+++ b/strbuf.h
@@ -340,14 +340,15 @@ extern void strbuf_vaddf(struct strbuf *sb, const char *fmt, va_list ap);
 
 /**
  * Add the time specified by `tm`, as formatted by `strftime`.
- * `tz_name` is used to expand %Z internally unless it's NULL.
  * `tz_offset` is in decimal hhmm format, e.g. -600 means six hours west
  * of Greenwich, and it's used to expand %z internally.  However, tokens
  * with modifiers (e.g. %Ez) are passed to `strftime`.
+ * `tzname_from_tz` when set, means let `strftime` format %Z, instead
+ * of intercepting it and doing our own formatting.
  */
 extern void strbuf_addftime(struct strbuf *sb, const char *fmt,
 			    const struct tm *tm, int tz_offset,
-			    const char *tz_name);
+			    const int omit_strftime_tz_name);
 
 /**
  * Read a given size of data from a FILE* pointer to the buffer.
-- 
2.13.1.611.g7e3b11ae1