Merge branch 'jk/date-mode-format'

Teach "git log" and friends a new "--date=format:..." option to
format timestamps using system's strftime(3).

* jk/date-mode-format:
  strbuf: make strbuf_addftime more robust
  introduce "format" date-mode
  convert "enum date_mode" into a struct
  show-branch: use DATE_RELATIVE instead of magic number

28 files changed, 172 insertions, 78 deletions

diff --git a/Documentation/rev-list-options.txt b/Documentation/rev-list-options.txt
index 77ac43923..a9b808fab 100644
--- a/Documentation/rev-list-options.txt
+++ b/Documentation/rev-list-options.txt
@@ -727,6 +727,11 @@ format, often found in email messages.
 +
 `--date=raw` shows the date in the internal raw Git format `%s %z` format.
 +
+`--date=format:...` feeds the format `...` to your system `strftime`.
+Use `--date=format:%c` to show the date in your system locale's
+preferred format.  See the `strftime` manual for a complete list of
+format placeholders.
++
 `--date=default` shows timestamps in the original time zone
 (either committer's or author's).
 
diff --git a/archive.c b/archive.c
index 936a5945d..01b0899b3 100644
--- a/archive.c
+++ b/archive.c
@@ -34,7 +34,7 @@ static void format_subst(const struct commit *commit,
 	char *to_free = NULL;
 	struct strbuf fmt = STRBUF_INIT;
 	struct pretty_print_context ctx = {0};
-	ctx.date_mode = DATE_NORMAL;
+	ctx.date_mode.type = DATE_NORMAL;
 	ctx.abbrev = DEFAULT_ABBREV;
 
 	if (src == buf->buf)
diff --git a/builtin/blame.c b/builtin/blame.c
index 272a22268..04e4864f8 100644
--- a/builtin/blame.c
+++ b/builtin/blame.c
@@ -51,7 +51,7 @@ static int xdl_opts;
 static int abbrev = -1;
 static int no_whole_file_rename;
 
-static enum date_mode blame_date_mode = DATE_ISO8601;
+static struct date_mode blame_date_mode = { DATE_ISO8601 };
 static size_t blame_date_width;
 
 static struct string_list mailmap;
@@ -1828,7 +1828,7 @@ static const char *format_time(unsigned long time, const char *tz_str,
 		size_t time_width;
 		int tz;
 		tz = atoi(tz_str);
-		time_str = show_date(time, tz, blame_date_mode);
+		time_str = show_date(time, tz, &blame_date_mode);
 		strbuf_addstr(&time_buf, time_str);
 		/*
 		 * Add space paddings to time_buf to display a fixed width
@@ -2188,7 +2188,7 @@ static int git_blame_config(const char *var, const char *value, void *cb)
 	if (!strcmp(var, "blame.date")) {
 		if (!value)
 			return config_error_nonbool(var);
-		blame_date_mode = parse_date_format(value);
+		parse_date_format(value, &blame_date_mode);
 		return 0;
 	}
 
@@ -2570,13 +2570,13 @@ parse_done:
 
 	if (cmd_is_annotate) {
 		output_option |= OUTPUT_ANNOTATE_COMPAT;
-		blame_date_mode = DATE_ISO8601;
+		blame_date_mode.type = DATE_ISO8601;
 	} else {
 		blame_date_mode = revs.date_mode;
 	}
 
 	/* The maximum width used to show the dates */
-	switch (blame_date_mode) {
+	switch (blame_date_mode.type) {
 	case DATE_RFC2822:
 		blame_date_width = sizeof("Thu, 19 Oct 2006 16:00:04 -0700");
 		break;
@@ -2605,6 +2605,9 @@ parse_done:
 	case DATE_NORMAL:
 		blame_date_width = sizeof("Thu Oct 19 16:00:04 2006 -0700");
 		break;
+	case DATE_STRFTIME:
+		blame_date_width = strlen(show_date(0, 0, &blame_date_mode)) + 1; /* add the null */
+		break;
 	}
 	blame_date_width -= 1; /* strip the null */
 
diff --git a/builtin/commit.c b/builtin/commit.c
index 254477fd1..7314f3388 100644
--- a/builtin/commit.c
+++ b/builtin/commit.c
@@ -856,7 +856,7 @@ static int prepare_to_commit(const char *index_file, const char *prefix,
 				_("%s"
 				"Date:      %s"),
 				ident_shown++ ? "" : "\n",
-				show_ident_date(&ai, DATE_NORMAL));
+				show_ident_date(&ai, DATE_MODE(NORMAL)));
 
 		if (!committer_ident_sufficiently_given())
 			status_printf_ln(s, GIT_COLOR_NORMAL,
@@ -1046,7 +1046,7 @@ static const char *find_author_by_nickname(const char *name)
 	commit = get_revision(&revs);
 	if (commit) {
 		struct pretty_print_context ctx = {0};
-		ctx.date_mode = DATE_NORMAL;
+		ctx.date_mode.type = DATE_NORMAL;
 		strbuf_release(&buf);
 		format_commit_message(commit, "%aN <%aE>", &buf, &ctx);
 		clear_mailmap(&mailmap);
diff --git a/builtin/log.c b/builtin/log.c
index c851c7cc2..b50ef7510 100644
--- a/builtin/log.c
+++ b/builtin/log.c
@@ -116,7 +116,7 @@ static void cmd_log_init_defaults(struct rev_info *rev)
 	DIFF_OPT_SET(&rev->diffopt, ALLOW_TEXTCONV);
 
 	if (default_date_mode)
-		rev->date_mode = parse_date_format(default_date_mode);
+		parse_date_format(default_date_mode, &rev->date_mode);
 	rev->diffopt.touched_flags = 0;
 }
 
@@ -956,7 +956,7 @@ static void make_cover_letter(struct rev_info *rev, int use_stdout,
 
 	msg = body;
 	pp.fmt = CMIT_FMT_EMAIL;
-	pp.date_mode = DATE_RFC2822;
+	pp.date_mode.type = DATE_RFC2822;
 	pp_user_info(&pp, NULL, &sb, committer, encoding);
 	pp_title_line(&pp, &msg, &sb, encoding, need_8bit_cte);
 	pp_remainder(&pp, &msg, &sb, 0);
diff --git a/builtin/shortlog.c b/builtin/shortlog.c
index c0bab6aaa..007cc66a0 100644
--- a/builtin/shortlog.c
+++ b/builtin/shortlog.c
@@ -138,7 +138,7 @@ void shortlog_add_commit(struct shortlog *log, struct commit *commit)
 		ctx.abbrev = log->abbrev;
 		ctx.subject = "";
 		ctx.after_subject = "";
-		ctx.date_mode = DATE_NORMAL;
+		ctx.date_mode.type = DATE_NORMAL;
 		ctx.output_encoding = get_log_output_encoding();
 		pretty_print_commit(&ctx, commit, &ufbuf);
 		buffer = ufbuf.buf;
diff --git a/builtin/show-branch.c b/builtin/show-branch.c
index 323f85746..c87c46eb3 100644
--- a/builtin/show-branch.c
+++ b/builtin/show-branch.c
@@ -784,7 +784,8 @@ int cmd_show_branch(int ac, const char **av, const char *prefix)
 			else
 				msg++;
 			reflog_msg[i] = xstrfmt("(%s) %s",
-						show_date(timestamp, tz, 1),
+						show_date(timestamp, tz,
+							  DATE_MODE(RELATIVE)),
 						msg);
 			free(logmsg);
 			sprintf(nth_desc, "%s@{%d}", *av, base+i);
diff --git a/cache.h b/cache.h
index 6997b2cd4..6bb711903 100644
--- a/cache.h
+++ b/cache.h
@@ -1049,18 +1049,30 @@ extern void *read_object_with_reference(const unsigned char *sha1,
 extern struct object *peel_to_type(const char *name, int namelen,
 				   struct object *o, enum object_type);
 
-enum date_mode {
-	DATE_NORMAL = 0,
-	DATE_RELATIVE,
-	DATE_SHORT,
-	DATE_LOCAL,
-	DATE_ISO8601,
-	DATE_ISO8601_STRICT,
-	DATE_RFC2822,
-	DATE_RAW
+struct date_mode {
+	enum date_mode_type {
+		DATE_NORMAL = 0,
+		DATE_RELATIVE,
+		DATE_SHORT,
+		DATE_LOCAL,
+		DATE_ISO8601,
+		DATE_ISO8601_STRICT,
+		DATE_RFC2822,
+		DATE_STRFTIME,
+		DATE_RAW
+	} type;
+	const char *strftime_fmt;
 };
 
-const char *show_date(unsigned long time, int timezone, enum date_mode mode);
+/*
+ * Convenience helper for passing a constant type, like:
+ *
+ *   show_date(t, tz, DATE_MODE(NORMAL));
+ */
+#define DATE_MODE(t) date_mode_from_type(DATE_##t)
+struct date_mode *date_mode_from_type(enum date_mode_type type);
+
+const char *show_date(unsigned long time, int timezone, const struct date_mode *mode);
 void show_date_relative(unsigned long time, int tz, const struct timeval *now,
 			struct strbuf *timebuf);
 int parse_date(const char *date, struct strbuf *out);
@@ -1070,7 +1082,7 @@ void datestamp(struct strbuf *out);
 #define approxidate(s) approxidate_careful((s), NULL)
 unsigned long approxidate_careful(const char *, int *);
 unsigned long approxidate_relative(const char *date, const struct timeval *now);
-enum date_mode parse_date_format(const char *format);
+void parse_date_format(const char *format, struct date_mode *mode);
 int date_overflows(unsigned long date);
 
 #define IDENT_STRICT	       1
@@ -1107,7 +1119,8 @@ extern int split_ident_line(struct ident_split *, const char *, int);
  * the ident_split. It will also sanity-check the values and produce
  * a well-known sentinel date if they appear bogus.
  */
-const char *show_ident_date(const struct ident_split *id, enum date_mode mode);
+const char *show_ident_date(const struct ident_split *id,
+			    const struct date_mode *mode);
 
 /*
  * Compare split idents for equality or strict ordering. Note that we
diff --git a/commit.h b/commit.h
index 4983bdd3d..5d58be001 100644
--- a/commit.h
+++ b/commit.h
@@ -145,7 +145,7 @@ struct pretty_print_context {
 	const char *subject;
 	const char *after_subject;
 	int preserve_subject;
-	enum date_mode date_mode;
+	struct date_mode date_mode;
 	unsigned date_mode_explicit:1;
 	int need_8bit_cte;
 	char *notes_message;
diff --git a/date.c b/date.c
index 733d1b29b..8f9156909 100644
--- a/date.c
+++ b/date.c
@@ -160,18 +160,27 @@ void show_date_relative(unsigned long time, int tz,
 		 (diff + 183) / 365);
 }
 
-const char *show_date(unsigned long time, int tz, enum date_mode mode)
+struct date_mode *date_mode_from_type(enum date_mode_type type)
+{
+	static struct date_mode mode;
+	if (type == DATE_STRFTIME)
+		die("BUG: cannot create anonymous strftime date_mode struct");
+	mode.type = type;
+	return &mode;
+}
+
+const char *show_date(unsigned long time, int tz, const struct date_mode *mode)
 {
 	struct tm *tm;
 	static struct strbuf timebuf = STRBUF_INIT;
 
-	if (mode == DATE_RAW) {
+	if (mode->type == DATE_RAW) {
 		strbuf_reset(&timebuf);
 		strbuf_addf(&timebuf, "%lu %+05d", time, tz);
 		return timebuf.buf;
 	}
 
-	if (mode == DATE_RELATIVE) {
+	if (mode->type == DATE_RELATIVE) {
 		struct timeval now;
 
 		strbuf_reset(&timebuf);
@@ -180,7 +189,7 @@ const char *show_date(unsigned long time, int tz, enum date_mode mode)
 		return timebuf.buf;
 	}
 
-	if (mode == DATE_LOCAL)
+	if (mode->type == DATE_LOCAL)
 		tz = local_tzoffset(time);
 
 	tm = time_to_tm(time, tz);
@@ -190,17 +199,17 @@ const char *show_date(unsigned long time, int tz, enum date_mode mode)
 	}
 
 	strbuf_reset(&timebuf);
-	if (mode == DATE_SHORT)
+	if (mode->type == DATE_SHORT)
 		strbuf_addf(&timebuf, "%04d-%02d-%02d", tm->tm_year + 1900,
 				tm->tm_mon + 1, tm->tm_mday);
-	else if (mode == DATE_ISO8601)
+	else if (mode->type == DATE_ISO8601)
 		strbuf_addf(&timebuf, "%04d-%02d-%02d %02d:%02d:%02d %+05d",
 				tm->tm_year + 1900,
 				tm->tm_mon + 1,
 				tm->tm_mday,
 				tm->tm_hour, tm->tm_min, tm->tm_sec,
 				tz);
-	else if (mode == DATE_ISO8601_STRICT) {
+	else if (mode->type == DATE_ISO8601_STRICT) {
 		char sign = (tz >= 0) ? '+' : '-';
 		tz = abs(tz);
 		strbuf_addf(&timebuf, "%04d-%02d-%02dT%02d:%02d:%02d%c%02d:%02d",
@@ -209,11 +218,13 @@ const char *show_date(unsigned long time, int tz, enum date_mode mode)
 				tm->tm_mday,
 				tm->tm_hour, tm->tm_min, tm->tm_sec,
 				sign, tz / 100, tz % 100);
-	} else if (mode == DATE_RFC2822)
+	} else if (mode->type == DATE_RFC2822)
 		strbuf_addf(&timebuf, "%.3s, %d %.3s %d %02d:%02d:%02d %+05d",
 			weekday_names[tm->tm_wday], tm->tm_mday,
 			month_names[tm->tm_mon], tm->tm_year + 1900,
 			tm->tm_hour, tm->tm_min, tm->tm_sec, tz);
+	else if (mode->type == DATE_STRFTIME)
+		strbuf_addftime(&timebuf, mode->strftime_fmt, tm);
 	else
 		strbuf_addf(&timebuf, "%.3s %.3s %d %02d:%02d:%02d %d%c%+05d",
 				weekday_names[tm->tm_wday],
@@ -221,7 +232,7 @@ const char *show_date(unsigned long time, int tz, enum date_mode mode)
 				tm->tm_mday,
 				tm->tm_hour, tm->tm_min, tm->tm_sec,
 				tm->tm_year + 1900,
-				(mode == DATE_LOCAL) ? 0 : ' ',
+				(mode->type == DATE_LOCAL) ? 0 : ' ',
 				tz);
 	return timebuf.buf;
 }
@@ -759,28 +770,31 @@ int parse_date(const char *date, struct strbuf *result)
 	return 0;
 }
 
-enum date_mode parse_date_format(const char *format)
+void parse_date_format(const char *format, struct date_mode *mode)
 {
 	if (!strcmp(format, "relative"))
-		return DATE_RELATIVE;
+		mode->type = DATE_RELATIVE;
 	else if (!strcmp(format, "iso8601") ||
 		 !strcmp(format, "iso"))
-		return DATE_ISO8601;
+		mode->type = DATE_ISO8601;
 	else if (!strcmp(format, "iso8601-strict") ||
 		 !strcmp(format, "iso-strict"))
-		return DATE_ISO8601_STRICT;
+		mode->type = DATE_ISO8601_STRICT;
 	else if (!strcmp(format, "rfc2822") ||
 		 !strcmp(format, "rfc"))
-		return DATE_RFC2822;
+		mode->type = DATE_RFC2822;
 	else if (!strcmp(format, "short"))
-		return DATE_SHORT;
+		mode->type = DATE_SHORT;
 	else if (!strcmp(format, "local"))
-		return DATE_LOCAL;
+		mode->type = DATE_LOCAL;
 	else if (!strcmp(format, "default"))
-		return DATE_NORMAL;
+		mode->type = DATE_NORMAL;
 	else if (!strcmp(format, "raw"))
-		return DATE_RAW;
-	else
+		mode->type = DATE_RAW;
+	else if (skip_prefix(format, "format:", &format)) {
+		mode->type = DATE_STRFTIME;
+		mode->strftime_fmt = xstrdup(format);
+	} else
 		die("unknown date format %s", format);
 }
 
diff --git a/fast-import.c b/fast-import.c
index 6a0c0ac57..2ad4fee07 100644
--- a/fast-import.c
+++ b/fast-import.c
@@ -423,7 +423,7 @@ static void write_crash_report(const char *err)
 	fprintf(rpt, "fast-import crash report:\n");
 	fprintf(rpt, "    fast-import process: %"PRIuMAX"\n", (uintmax_t) getpid());
 	fprintf(rpt, "    parent process     : %"PRIuMAX"\n", (uintmax_t) getppid());
-	fprintf(rpt, "    at %s\n", show_date(time(NULL), 0, DATE_LOCAL));
+	fprintf(rpt, "    at %s\n", show_date(time(NULL), 0, DATE_MODE(LOCAL)));
 	fputc('\n', rpt);
 
 	fputs("fatal: ", rpt);
diff --git a/gettext.c b/gettext.c
index 7378ba287..a268a2c52 100644
--- a/gettext.c
+++ b/gettext.c
@@ -162,6 +162,7 @@ void git_setup_gettext(void)
 		podir = GIT_LOCALE_PATH;
 	bindtextdomain("git", podir);
 	setlocale(LC_MESSAGES, "");
+	setlocale(LC_TIME, "");
 	init_gettext_charset("git");
 	textdomain("git");
 }
diff --git a/http-backend.c b/http-backend.c
index 501bf797c..b977c006a 100644
--- a/http-backend.c
+++ b/http-backend.c
@@ -92,7 +92,7 @@ static void hdr_int(const char *name, uintmax_t value)
 
 static void hdr_date(const char *name, unsigned long when)
 {
-	const char *value = show_date(when, 0, DATE_RFC2822);
+	const char *value = show_date(when, 0, DATE_MODE(RFC2822));
 	hdr_str(name, value);
 }
 
diff --git a/log-tree.c b/log-tree.c
index e2f6de73e..7b1b57aaf 100644
--- a/log-tree.c
+++ b/log-tree.c
@@ -640,7 +640,7 @@ void show_log(struct rev_info *opt)
 			 */
 			show_reflog_message(opt->reflog_info,
 					    opt->commit_format == CMIT_FMT_ONELINE,
-					    opt->date_mode,
+					    &opt->date_mode,
 					    opt->date_mode_explicit);
 			if (opt->commit_format == CMIT_FMT_ONELINE)
 				return;
diff --git a/pretty.c b/pretty.c
index 7b4930418..151c2ae31 100644
--- a/pretty.c
+++ b/pretty.c
@@ -399,7 +399,7 @@ static void add_rfc2047(struct strbuf *sb, const char *line, size_t len,
 }
 
 const char *show_ident_date(const struct ident_split *ident,
-			    enum date_mode mode)
+			    const struct date_mode *mode)
 {
 	unsigned long date = 0;
 	long tz = 0;
@@ -489,15 +489,15 @@ void pp_user_info(struct pretty_print_context *pp,
 	switch (pp->fmt) {
 	case CMIT_FMT_MEDIUM:
 		strbuf_addf(sb, "Date:   %s\n",
-			    show_ident_date(&ident, pp->date_mode));
+			    show_ident_date(&ident, &pp->date_mode));
 		break;
 	case CMIT_FMT_EMAIL:
 		strbuf_addf(sb, "Date: %s\n",
-			    show_ident_date(&ident, DATE_RFC2822));
+			    show_ident_date(&ident, DATE_MODE(RFC2822)));
 		break;
 	case CMIT_FMT_FULLER:
 		strbuf_addf(sb, "%sDate: %s\n", what,
-			    show_ident_date(&ident, pp->date_mode));
+			    show_ident_date(&ident, &pp->date_mode));
 		break;
 	default:
 		/* notin' */
@@ -671,7 +671,8 @@ static int mailmap_name(const char **email, size_t *email_len,
 }
 
 static size_t format_person_part(struct strbuf *sb, char part,
-				 const char *msg, int len, enum date_mode dmode)
+				 const char *msg, int len,
+				 const struct date_mode *dmode)
 {
 	/* currently all placeholders have same length */
 	const int placeholder_len = 2;
@@ -711,16 +712,16 @@ static size_t format_person_part(struct strbuf *sb, char part,
 		strbuf_addstr(sb, show_ident_date(&s, dmode));
 		return placeholder_len;
 	case 'D':	/* date, RFC2822 style */
-		strbuf_addstr(sb, show_ident_date(&s, DATE_RFC2822));
+		strbuf_addstr(sb, show_ident_date(&s, DATE_MODE(RFC2822)));
 		return placeholder_len;
 	case 'r':	/* date, relative */
-		strbuf_addstr(sb, show_ident_date(&s, DATE_RELATIVE));
+		strbuf_addstr(sb, show_ident_date(&s, DATE_MODE(RELATIVE)));
 		return placeholder_len;
 	case 'i':	/* date, ISO 8601-like */
-		strbuf_addstr(sb, show_ident_date(&s, DATE_ISO8601));
+		strbuf_addstr(sb, show_ident_date(&s, DATE_MODE(ISO8601)));
 		return placeholder_len;
 	case 'I':	/* date, ISO 8601 strict */
-		strbuf_addstr(sb, show_ident_date(&s, DATE_ISO8601_STRICT));
+		strbuf_addstr(sb, show_ident_date(&s, DATE_MODE(ISO8601_STRICT)));
 		return placeholder_len;
 	}
 
@@ -933,7 +934,7 @@ static void rewrap_message_tail(struct strbuf *sb,
 static int format_reflog_person(struct strbuf *sb,
 				char part,
 				struct reflog_walk_info *log,
-				enum date_mode dmode)
+				const struct date_mode *dmode)
 {
 	const char *ident;
 
@@ -1185,7 +1186,7 @@ static size_t format_commit_one(struct strbuf *sb, /* in UTF-8 */
 			if (c->pretty_ctx->reflog_info)
 				get_reflog_selector(sb,
 						    c->pretty_ctx->reflog_info,
-						    c->pretty_ctx->date_mode,
+						    &c->pretty_ctx->date_mode,
 						    c->pretty_ctx->date_mode_explicit,
 						    (placeholder[1] == 'd'));
 			return 2;
@@ -1200,7 +1201,7 @@ static size_t format_commit_one(struct strbuf *sb, /* in UTF-8 */
 			return format_reflog_person(sb,
 						    placeholder[1],
 						    c->pretty_ctx->reflog_info,
-						    c->pretty_ctx->date_mode);
+						    &c->pretty_ctx->date_mode);
 		}
 		return 0;	/* unknown %g placeholder */
 	case 'N':
@@ -1251,11 +1252,11 @@ static size_t format_commit_one(struct strbuf *sb, /* in UTF-8 */
 	case 'a':	/* author ... */
 		return format_person_part(sb, placeholder[1],
 				   msg + c->author.off, c->author.len,
-				   c->pretty_ctx->date_mode);
+				   &c->pretty_ctx->date_mode);
 	case 'c':	/* committer ... */
 		return format_person_part(sb, placeholder[1],
 				   msg + c->committer.off, c->committer.len,
-				   c->pretty_ctx->date_mode);
+				   &c->pretty_ctx->date_mode);
 	case 'e':	/* encoding */
 		if (c->commit_encoding)
 			strbuf_addstr(sb, c->commit_encoding);
diff --git a/ref-filter.c b/ref-filter.c
index 6e09da88c..f38dee4f6 100644
--- a/ref-filter.c
+++ b/ref-filter.c
@@ -362,7 +362,7 @@ static void grab_date(const char *buf, struct atom_value *v, const char *atomnam
 	char *zone;
 	unsigned long timestamp;
 	long tz;
-	enum date_mode date_mode = DATE_NORMAL;
+	struct date_mode date_mode = { DATE_NORMAL };
 	const char *formatp;
 
 	/*
@@ -374,7 +374,7 @@ static void grab_date(const char *buf, struct atom_value *v, const char *atomnam
 	formatp = strchr(atomname, ':');
 	if (formatp != NULL) {
 		formatp++;
-		date_mode = parse_date_format(formatp);
+		parse_date_format(formatp, &date_mode);
 	}
 
 	if (!eoemail)
@@ -385,7 +385,7 @@ static void grab_date(const char *buf, struct atom_value *v, const char *atomnam
 	tz = strtol(zone, NULL, 10);
 	if ((tz == LONG_MIN || tz == LONG_MAX) && errno == ERANGE)
 		goto bad;
-	v->s = xstrdup(show_date(timestamp, tz, date_mode));
+	v->s = xstrdup(show_date(timestamp, tz, &date_mode));
 	v->ul = timestamp;
 	return;
  bad:
diff --git a/reflog-walk.c b/reflog-walk.c
index 222de762e..f8e743a23 100644
--- a/reflog-walk.c
+++ b/reflog-walk.c
@@ -249,7 +249,7 @@ void fake_reflog_parent(struct reflog_walk_info *info, struct commit *commit)
 
 void get_reflog_selector(struct strbuf *sb,
 			 struct reflog_walk_info *reflog_info,
-			 enum date_mode dmode, int force_date,
+			 const struct date_mode *dmode, int force_date,
 			 int shorten)
 {
 	struct commit_reflog *commit_reflog = reflog_info->last_commit_reflog;
@@ -311,7 +311,7 @@ const char *get_reflog_ident(struct reflog_walk_info *reflog_info)
 }
 
 void show_reflog_message(struct reflog_walk_info *reflog_info, int oneline,
-			 enum date_mode dmode, int force_date)
+			 const struct date_mode *dmode, int force_date)
 {
 	if (reflog_info && reflog_info->last_commit_reflog) {
 		struct commit_reflog *commit_reflog = reflog_info->last_commit_reflog;
diff --git a/reflog-walk.h b/reflog-walk.h
index a9bd60e32..27886f793 100644
--- a/reflog-walk.h
+++ b/reflog-walk.h
@@ -11,13 +11,13 @@ extern int add_reflog_for_walk(struct reflog_walk_info *info,
 extern void fake_reflog_parent(struct reflog_walk_info *info,
 		struct commit *commit);
 extern void show_reflog_message(struct reflog_walk_info *info, int,
-				enum date_mode, int force_date);
+				const struct date_mode *, int force_date);
 extern void get_reflog_message(struct strbuf *sb,
 		struct reflog_walk_info *reflog_info);
 extern const char *get_reflog_ident(struct reflog_walk_info *reflog_info);
 extern void get_reflog_selector(struct strbuf *sb,
 		struct reflog_walk_info *reflog_info,
-		enum date_mode dmode, int force_date,
+		const struct date_mode *dmode, int force_date,
 		int shorten);
 
 #endif
diff --git a/refs.c b/refs.c
index fb568d7a3..ce8cd8d45 100644
--- a/refs.c
+++ b/refs.c
@@ -3436,14 +3436,14 @@ static int read_ref_at_ent(unsigned char *osha1, unsigned char *nsha1,
 			hashcpy(cb->sha1, nsha1);
 			if (hashcmp(cb->osha1, nsha1))
 				warning("Log for ref %s has gap after %s.",
-					cb->refname, show_date(cb->date, cb->tz, DATE_RFC2822));
+					cb->refname, show_date(cb->date, cb->tz, DATE_MODE(RFC2822)));
 		}
 		else if (cb->date == cb->at_time)
 			hashcpy(cb->sha1, nsha1);
 		else if (hashcmp(nsha1, cb->sha1))
 			warning("Log for ref %s unexpectedly ended on %s.",
 				cb->refname, show_date(cb->date, cb->tz,
-						   DATE_RFC2822));
+						       DATE_MODE(RFC2822)));
 		hashcpy(cb->osha1, osha1);
 		hashcpy(cb->nsha1, nsha1);
 		cb->found_it = 1;
diff --git a/revision.c b/revision.c
index ab97ffd45..cf60c5d81 100644
--- a/revision.c
+++ b/revision.c
@@ -1996,10 +1996,10 @@ static int handle_revision_opt(struct rev_info *revs, int argc, const char **arg
 	} else if (!strcmp(arg, "--full-history")) {
 		revs->simplify_history = 0;
 	} else if (!strcmp(arg, "--relative-date")) {
-		revs->date_mode = DATE_RELATIVE;
+		revs->date_mode.type = DATE_RELATIVE;
 		revs->date_mode_explicit = 1;
 	} else if ((argcount = parse_long_opt("date", argv, &optarg))) {
-		revs->date_mode = parse_date_format(optarg);
+		parse_date_format(optarg, &revs->date_mode);
 		revs->date_mode_explicit = 1;
 		return argcount;
 	} else if (!strcmp(arg, "--log-size")) {
diff --git a/revision.h b/revision.h
index 0ea8b4e25..5bc968684 100644
--- a/revision.h
+++ b/revision.h
@@ -146,7 +146,7 @@ struct rev_info {
 			track_first_time:1,
 			linear:1;
 
-	enum date_mode date_mode;
+	struct date_mode date_mode;
 
 	unsigned int	abbrev;
 	enum cmit_fmt	commit_format;
diff --git a/sha1_name.c b/sha1_name.c
index e57513e61..da6874c15 100644
--- a/sha1_name.c
+++ b/sha1_name.c
@@ -576,7 +576,7 @@ static int get_sha1_basic(const char *str, int len, unsigned char *sha1,
 				if (!(flags & GET_SHA1_QUIETLY)) {
 					warning("Log for '%.*s' only goes "
 						"back to %s.", len, str,
-						show_date(co_time, co_tz, DATE_RFC2822));
+						show_date(co_time, co_tz, DATE_MODE(RFC2822)));
 				}
 			} else {
 				if (flags & GET_SHA1_QUIETLY) {
diff --git a/strbuf.c b/strbuf.c
index bbaf32eef..cce5eed14 100644
--- a/strbuf.c
+++ b/strbuf.c
@@ -710,3 +710,36 @@ char *xstrfmt(const char *fmt, ...)
 
 	return ret;
 }
+
+void strbuf_addftime(struct strbuf *sb, const char *fmt, const struct tm *tm)
+{
+	size_t hint = 128;
+	size_t len;
+
+	if (!*fmt)
+		return;
+
+	strbuf_grow(sb, hint);
+	len = strftime(sb->buf + sb->len, sb->alloc - sb->len, fmt, tm);
+
+	if (!len) {
+		/*
+		 * strftime reports "0" if it could not fit the result in the buffer.
+		 * Unfortunately, it also reports "0" if the requested time string
+		 * takes 0 bytes. So our strategy is to munge the format so that the
+		 * output contains at least one character, and then drop the extra
+		 * character before returning.
+		 */
+		struct strbuf munged_fmt = STRBUF_INIT;
+		strbuf_addf(&munged_fmt, "%s ", fmt);
+		while (!len) {
+			hint *= 2;
+			strbuf_grow(sb, hint);
+			len = strftime(sb->buf + sb->len, sb->alloc - sb->len,
+				       munged_fmt.buf, tm);
+		}
+		strbuf_release(&munged_fmt);
+		len--; /* drop munged space */
+	}
+	strbuf_setlen(sb, sb->len + len);
+}
diff --git a/strbuf.h b/strbuf.h
index 4a48c0031..aef279465 100644
--- a/strbuf.h
+++ b/strbuf.h
@@ -345,6 +345,11 @@ __attribute__((format (printf,2,0)))
 extern void strbuf_vaddf(struct strbuf *sb, const char *fmt, va_list ap);
 
 /**
+ * Add the time specified by `tm`, as formatted by `strftime`.
+ */
+extern void strbuf_addftime(struct strbuf *sb, const char *fmt, const struct tm *tm);
+
+/**
  * Read a given size of data from a FILE* pointer to the buffer.
  *
  * NOTE: The buffer is rewound if the read fails. If -1 is returned,
diff --git a/submodule.c b/submodule.c
index 15e90d1c1..700bbf4fc 100644
--- a/submodule.c
+++ b/submodule.c
@@ -993,7 +993,7 @@ static void print_commit(struct commit *commit)
 {
 	struct strbuf sb = STRBUF_INIT;
 	struct pretty_print_context ctx = {0};
-	ctx.date_mode = DATE_NORMAL;
+	ctx.date_mode.type = DATE_NORMAL;
 	format_commit_message(commit, " %h: %m %s", &sb, &ctx);
 	fprintf(stderr, "%s\n", sb.buf);
 	strbuf_release(&sb);
diff --git a/t/t6300-for-each-ref.sh b/t/t6300-for-each-ref.sh
index 24fc2ba55..7c9bec763 100755
--- a/t/t6300-for-each-ref.sh
+++ b/t/t6300-for-each-ref.sh
@@ -227,6 +227,24 @@ test_expect_success 'Check format "rfc2822" date fields output' '
 	test_cmp expected actual
 '
 
+test_expect_success 'Check format of strftime date fields' '
+	echo "my date is 2006-07-03" >expected &&
+	git for-each-ref \
+	  --format="%(authordate:format:my date is %Y-%m-%d)" \
+	  refs/heads >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'exercise strftime with odd fields' '
+	echo >expected &&
+	git for-each-ref --format="%(authordate:format:)" refs/heads >actual &&
+	test_cmp expected actual &&
+	long="long format -- $_z40$_z40$_z40$_z40$_z40$_z40$_z40" &&
+	echo $long >expected &&
+	git for-each-ref --format="%(authordate:format:$long)" refs/heads >actual &&
+	test_cmp expected actual
+'
+
 cat >expected <<\EOF
 refs/heads/master
 refs/remotes/origin/master
diff --git a/test-date.c b/test-date.c
index 94a6997a8..63f373557 100644
--- a/test-date.c
+++ b/test-date.c
@@ -29,7 +29,7 @@ static void parse_dates(char **argv, struct timeval *now)
 		parse_date(*argv, &result);
 		if (sscanf(result.buf, "%lu %d", &t, &tz) == 2)
 			printf("%s -> %s\n",
-			       *argv, show_date(t, tz, DATE_ISO8601));
+			       *argv, show_date(t, tz, DATE_MODE(ISO8601)));
 		else
 			printf("%s -> bad\n", *argv);
 	}
@@ -41,7 +41,7 @@ static void parse_approxidate(char **argv, struct timeval *now)
 	for (; *argv; argv++) {
 		time_t t;
 		t = approxidate_relative(*argv, now);
-		printf("%s -> %s\n", *argv, show_date(t, 0, DATE_ISO8601));
+		printf("%s -> %s\n", *argv, show_date(t, 0, DATE_MODE(ISO8601)));
 	}
 }
 
diff --git a/test-revision-walking.c b/test-revision-walking.c
index 3ade02c72..285f06b7f 100644
--- a/test-revision-walking.c
+++ b/test-revision-walking.c
@@ -17,7 +17,7 @@ static void print_commit(struct commit *commit)
 {
 	struct strbuf sb = STRBUF_INIT;
 	struct pretty_print_context ctx = {0};
-	ctx.date_mode = DATE_NORMAL;
+	ctx.date_mode.type = DATE_NORMAL;
 	format_commit_message(commit, " %m %s", &sb, &ctx);
 	printf("%s\n", sb.buf);
 	strbuf_release(&sb);