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, 23 insertions, 12 deletions

diff --git a/cache.h b/cache.h
index 4f554664c5..0974fa797c 100644
--- a/cache.h
+++ b/cache.h
@@ -1105,18 +1105,28 @@ 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_RAW
+	} type;
 };
 
-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);
@@ -1126,7 +1136,7 @@ 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
@@ -1163,7 +1173,8 @@ 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