pretty: give placeholders to reflog identity

When doing a reflog walk, you can get some information about
the reflog (such as the subject line), but not the identity
information (i.e., name and email).

Let's make those available, mimicing the options for author
and committer identity.

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

Documentation/pretty-formats.txt

@@ -132,6 +132,10 @@ The placeholders are:
 - '%N': commit notes
 - '%gD': reflog selector, e.g., `refs/stash@\{1\}`
 - '%gd': shortened reflog selector, e.g., `stash@\{1\}`
+- '%gn': reflog identity name
+- '%gN': reflog identity name (respecting .mailmap, see linkgit:git-shortlog[1] or linkgit:git-blame[1])
+- '%ge': reflog identity email
+- '%gE': reflog identity email (respecting .mailmap, see linkgit:git-shortlog[1] or linkgit:git-blame[1])
 - '%gs': reflog subject
 - '%Cred': switch color to red
 - '%Cgreen': switch color to green

pretty.c

@@ -822,6 +822,23 @@ static void rewrap_message_tail(struct strbuf *sb,
 	c->indent2 = new_indent2;
 }
 
+static int format_reflog_person(struct strbuf *sb,
+				char part,
+				struct reflog_walk_info *log,
+				enum date_mode dmode)
+{
+	const char *ident;
+
+	if (!log)
+		return 2;
+
+	ident = get_reflog_ident(log);
+	if (!ident)
+		return 2;
+
+	return format_person_part(sb, part, ident, strlen(ident), dmode);
+}
+
 static size_t format_commit_one(struct strbuf *sb, const char *placeholder,
 				void *context)
 {
@@ -963,6 +980,14 @@ static size_t format_commit_one(struct strbuf *sb, const char *placeholder,
 			if (c->pretty_ctx->reflog_info)
 				get_reflog_message(sb, c->pretty_ctx->reflog_info);
 			return 2;
+		case 'n':
+		case 'N':
+		case 'e':
+		case 'E':
+			return format_reflog_person(sb,
+						    placeholder[1],
+						    c->pretty_ctx->reflog_info,
+						    c->pretty_ctx->date_mode);
 		}
 		return 0;	/* unknown %g placeholder */
 	case 'N':

reflog-walk.c

@@ -291,6 +291,18 @@ void get_reflog_message(struct strbuf *sb,
 	strbuf_add(sb, info->message, len);
 }
 
+const char *get_reflog_ident(struct reflog_walk_info *reflog_info)
+{
+	struct commit_reflog *commit_reflog = reflog_info->last_commit_reflog;
+	struct reflog_info *info;
+
+	if (!commit_reflog)
+		return NULL;
+
+	info = &commit_reflog->reflogs->items[commit_reflog->recno+1];
+	return info->email;
+}
+
 void show_reflog_message(struct reflog_walk_info *reflog_info, int oneline,
 	enum date_mode dmode)
 {

reflog-walk.h

@@ -14,6 +14,7 @@ extern void show_reflog_message(struct reflog_walk_info *info, int,
 		enum date_mode);
 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,

t/t6006-rev-list-format.sh

@@ -267,6 +267,12 @@ test_expect_success '%gd shortens ref name' '
 	test_cmp expect.gd-short actual.gd-short
 '
 
+test_expect_success 'reflog identity' '
+	echo "C O Mitter:committer@example.com" >expect &&
+	git log -g -1 --format="%gn:%ge" >actual &&
+	test_cmp expect actual
+'
+
 test_expect_success 'oneline with empty message' '
 	git commit -m "dummy" --allow-empty &&
 	git commit -m "dummy" --allow-empty &&