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, 2 insertions, 2 deletions

diff --git a/test-date.c b/test-date.c
index 94a6997..63f3735 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)));
 	}
 }