convert "enum date_mode" into a struct

In preparation for adding date modes that may carry extra
information beyond the mode itself, this patch converts the
date_mode enum into a struct.

Most of the conversion is fairly straightforward; we pass
the struct as a pointer and dereference the type field where
necessary. Locations that declare a date_mode can use a "{}"
constructor.  However, the tricky case is where we use the
enum labels as constants, like:

  show_date(t, tz, DATE_NORMAL);

Ideally we could say:

  show_date(t, tz, &{ DATE_NORMAL });

but of course C does not allow that. Likewise, we cannot
cast the constant to a struct, because we need to pass an
actual address. Our options are basically:

  1. Manually add a "struct date_mode d = { DATE_NORMAL }"
     definition to each caller, and pass "&d". This makes
     the callers uglier, because they sometimes do not even
     have their own scope (e.g., they are inside a switch
     statement).

  2. Provide a pre-made global "date_normal" struct that can
     be passed by address. We'd also need "date_rfc2822",
     "date_iso8601", and so forth. But at least the ugliness
     is defined in one place.

  3. Provide a wrapper that generates the correct struct on
     the fly. The big downside is that we end up pointing to
     a single global, which makes our wrapper non-reentrant.
     But show_date is already not reentrant, so it does not
     matter.

This patch implements 3, along with a minor macro to keep
the size of the callers sane.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 3 insertions, 3 deletions

diff --git a/builtin/for-each-ref.c b/builtin/for-each-ref.c
index cb7db23..d757837 100644
--- a/builtin/for-each-ref.c
+++ b/builtin/for-each-ref.c
@@ -389,7 +389,7 @@ 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;
 
 	/*
@@ -401,7 +401,7 @@ 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)
@@ -412,7 +412,7 @@ 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: