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/refs.c b/refs.c
index 7ac05cf21a..83a6bea3a5 100644
--- a/refs.c
+++ b/refs.c
@@ -3371,14 +3371,14 @@ 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;