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/reflog-walk.h b/reflog-walk.h
index a9bd60e32d..27886f793e 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