commit: search author pattern against mailmap

"git commit --author=$name" sets the author to one whose name
matches the given string from existing commits, when $name is not in
the "Name <e-mail>" format. However, it does not honor the mailmap
to use the canonical name for the author found this way.

Fix it by telling the logic to find a matching existing author to
honor the mailmap, and use the name and email after applying the
mailmap.

Signed-off-by: Antoine Pelisse <apelisse@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/commit.c

@@ -30,6 +30,7 @@
 #include "column.h"
 #include "sequencer.h"
 #include "notes-utils.h"
+#include "mailmap.h"
 
 static const char * const builtin_commit_usage[] = {
 	N_("git commit [options] [--] <pathspec>..."),
@@ -935,6 +936,7 @@ static const char *find_author_by_nickname(const char *name)
 	struct rev_info revs;
 	struct commit *commit;
 	struct strbuf buf = STRBUF_INIT;
+	struct string_list mailmap = STRING_LIST_INIT_NODUP;
 	const char *av[20];
 	int ac = 0;
 
@@ -945,13 +947,17 @@ static const char *find_author_by_nickname(const char *name)
 	av[++ac] = buf.buf;
 	av[++ac] = NULL;
 	setup_revisions(ac, av, &revs, NULL);
+	revs.mailmap = &mailmap;
+	read_mailmap(revs.mailmap, NULL);
+
 	prepare_revision_walk(&revs);
 	commit = get_revision(&revs);
 	if (commit) {
 		struct pretty_print_context ctx = {0};
 		ctx.date_mode = DATE_NORMAL;
 		strbuf_release(&buf);
-		format_commit_message(commit, "%an <%ae>", &buf, &ctx);
+		format_commit_message(commit, "%aN <%aE>", &buf, &ctx);
+		clear_mailmap(&mailmap);
 		return strbuf_detach(&buf, NULL);
 	}
 	die(_("No existing author found with '%s'"), name);

t/t4203-mailmap.sh

@@ -470,4 +470,15 @@ test_expect_success 'Blame output (complex mapping)' '
 	test_cmp expect actual.fuzz
 '
 
+cat >expect <<\EOF
+Some Dude <some@dude.xx>
+EOF
+
+test_expect_success 'commit --author honors mailmap' '
+	test_must_fail git commit --author "nick" --allow-empty -meight &&
+	git commit --author "Some Dude" --allow-empty -meight &&
+	git show --pretty=format:"%an <%ae>%n" >actual &&
+	test_cmp expect actual
+'
+
 test_done