shortlog: group by committer information

In some situations you may want to group the commits not by author,
but by committer instead.

For example, when I just wanted to look up what I'm still missing from
linux-next in the current merge window, I don't care so much about who
wrote a patch, as what git tree it came from, which generally boils
down to "who committed it".

So make git shortlog take a "-c" or "--committer" option to switch
grouping to that.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/shortlog.c

@@ -117,11 +117,15 @@ static void read_from_stdin(struct shortlog *log)
 {
 	struct strbuf author = STRBUF_INIT;
 	struct strbuf oneline = STRBUF_INIT;
+	static const char *author_match[2] = { "Author: ", "author " };
+	static const char *committer_match[2] = { "Commit: ", "committer " };
+	const char **match;
 
+	match = log->committer ? committer_match : author_match;
 	while (strbuf_getline_lf(&author, stdin) != EOF) {
 		const char *v;
-		if (!skip_prefix(author.buf, "Author: ", &v) &&
+		if (!skip_prefix(author.buf, match[0], &v) &&
-		    !skip_prefix(author.buf, "author ", &v))
+		    !skip_prefix(author.buf, match[1], &v))
 			continue;
 		while (strbuf_getline_lf(&oneline, stdin) != EOF &&
 		       oneline.len)
@@ -140,6 +144,7 @@ void shortlog_add_commit(struct shortlog *log, struct commit *commit)
 	struct strbuf author = STRBUF_INIT;
 	struct strbuf oneline = STRBUF_INIT;
 	struct pretty_print_context ctx = {0};
+	const char *fmt;
 
 	ctx.fmt = CMIT_FMT_USERFORMAT;
 	ctx.abbrev = log->abbrev;
@@ -148,7 +153,9 @@ void shortlog_add_commit(struct shortlog *log, struct commit *commit)
 	ctx.date_mode.type = DATE_NORMAL;
 	ctx.output_encoding = get_log_output_encoding();
 
-	format_commit_message(commit, "%an <%ae>", &author, &ctx);
+	fmt = log->committer ? "%cn <%ce>" : "%an <%ae>";
+
+	format_commit_message(commit, fmt, &author, &ctx);
 	if (!log->summary) {
 		if (log->user_format)
 			pretty_print_commit(&ctx, commit, &oneline);
@@ -238,6 +245,8 @@ int cmd_shortlog(int argc, const char **argv, const char *prefix)
 	int nongit = !startup_info->have_repository;
 
 	const struct option options[] = {
+		OPT_BOOL('c', "committer", &log.committer,
+			 N_("Group by committer rather than author")),
 		OPT_BOOL('n', "numbered", &log.sort_by_number,
 			 N_("sort output according to the number of commits per author")),
 		OPT_BOOL('s', "summary", &log.summary,

shortlog.h

@@ -13,6 +13,7 @@ struct shortlog {
 	int in2;
 	int user_format;
 	int abbrev;
+	int committer;
 
 	char *common_repo_prefix;
 	int email;