shortlog: parse trailer idents

Trailers don't necessarily contain name/email identity values, so
shortlog has so far treated them as opaque strings. However, since many
trailers do contain identities, it's useful to treat them as such when
they can be parsed. That lets "-e" work as usual, as well as mailmap.

When they can't be parsed, we'll continue with the old behavior of
treating them as a single string (there's no new test for that here,
since the existing tests cover a trailer like this).

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

Documentation/git-shortlog.txt

@@ -64,9 +64,10 @@ Likewise, commits with multiple trailers (e.g., multiple signoffs) may
 be counted more than once (but only once per unique trailer value in
 that commit).
 +
-The contents of each trailer value are taken literally and completely.
-No mailmap is applied, and the `-e` option has no effect (if the trailer
-contains a username and email, they are both always shown).
+Shortlog will attempt to parse each trailer value as a `name <email>`
+identity. If successful, the mailmap is applied and the email is omitted
+unless the `--email` option is specified. If the value cannot be parsed
+as an identity, it will be taken literally and completely.
 
 -c::
 --committer::

builtin/shortlog.c

@@ -228,6 +228,7 @@ static void insert_records_from_trailers(struct shortlog *log,
 	struct trailer_iterator iter;
 	const char *commit_buffer, *body;
 	struct strset dups = STRSET_INIT;
+	struct strbuf ident = STRBUF_INIT;
 
 	/*
 	 * Using format_commit_message("%B") would be simpler here, but
@@ -245,12 +246,17 @@ static void insert_records_from_trailers(struct shortlog *log,
 		if (strcasecmp(iter.key.buf, log->trailer))
 			continue;
 
+		strbuf_reset(&ident);
+		if (!parse_ident(log, &ident, value))
+			value = ident.buf;
+
 		if (strset_check_and_add(&dups, value))
 			continue;
 		insert_one_record(log, value, oneline);
 	}
 	trailer_iterator_release(&iter);
 
+	strbuf_release(&ident);
 	strset_clear(&dups);
 	unuse_commit_buffer(commit, commit_buffer);
 }

t/t4201-shortlog.sh

@@ -230,10 +230,30 @@ test_expect_success 'shortlog --group=trailer:signed-off-by' '
 	     2	C O Mitter <committer@example.com>
 	     1	SOB One <sob@example.com>
 	EOF
+	git shortlog -nse --group=trailer:signed-off-by HEAD >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'trailer idents are split' '
+	cat >expect <<-\EOF &&
+	     2	C O Mitter
+	     1	SOB One
+	EOF
 	git shortlog -ns --group=trailer:signed-off-by HEAD >actual &&
 	test_cmp expect actual
 '
 
+test_expect_success 'trailer idents are mailmapped' '
+	cat >expect <<-\EOF &&
+	     2	C O Mitter
+	     1	Another Name
+	EOF
+	echo "Another Name <sob@example.com>" >mail.map &&
+	git -c mailmap.file=mail.map shortlog -ns \
+		--group=trailer:signed-off-by HEAD >actual &&
+	test_cmp expect actual
+'
+
 test_expect_success 'shortlog de-duplicates trailers in a single commit' '
 	git commit --allow-empty -F - <<-\EOF &&
 	subject one