Add pretty format %aN which gives the author name, respecting .mailmap

The pretty format %an does not respect .mailmap, but gives the exact
author name recorded in the commit.  Sometimes it is more desirable,
however, to look if the email has another name mapped to it in .mailmap.

This commit adds %aN (and %cN for the committer name) to do exactly that.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/pretty-formats.txt

@@ -101,6 +101,7 @@ The placeholders are:
 - '%P': parent hashes
 - '%p': abbreviated parent hashes
 - '%an': author name
+- '%aN': author name (respecting .mailmap)
 - '%ae': author email
 - '%ad': author date
 - '%aD': author date, RFC2822 style
@@ -108,6 +109,7 @@ The placeholders are:
 - '%at': author date, UNIX timestamp
 - '%ai': author date, ISO 8601 format
 - '%cn': committer name
+- '%cN': committer name (respecting .mailmap)
 - '%ce': committer email
 - '%cd': committer date
 - '%cD': committer date, RFC2822 style

pretty.c

@@ -3,6 +3,8 @@
 #include "utf8.h"
 #include "diff.h"
 #include "revision.h"
+#include "path-list.h"
+#include "mailmap.h"
 
 static char *user_format;
 
@@ -288,6 +290,25 @@ static char *logmsg_reencode(const struct commit *commit,
 	return out;
 }
 
+static int mailmap_name(struct strbuf *sb, const char *email)
+{
+	static struct path_list *mail_map;
+	char buffer[1024];
+
+	if (!mail_map) {
+		mail_map = xcalloc(1, sizeof(*mail_map));
+		read_mailmap(mail_map, ".mailmap", NULL);
+	}
+
+	if (!mail_map->nr)
+		return -1;
+
+	if (!map_email(mail_map, email, buffer, sizeof(buffer)))
+		return -1;
+	strbuf_addstr(sb, buffer);
+	return 0;
+}
+
 static size_t format_person_part(struct strbuf *sb, char part,
                                const char *msg, int len)
 {
@@ -309,9 +330,11 @@ static size_t format_person_part(struct strbuf *sb, char part,
 	if (end >= len - 2)
 		goto skip;
 
-	if (part == 'n') {	/* name */
+	if (part == 'n' || part == 'N') {	/* name */
 		while (end > 0 && isspace(msg[end - 1]))
 			end--;
+		if (part != 'N' || !msg[end] || !msg[end + 1] ||
+		    mailmap_name(sb, msg + end + 2) < 0)
 			strbuf_add(sb, msg, end);
 		return placeholder_len;
 	}