am: avoid diff_opt_parse()

diff_opt_parse() is a heavy hammer to just set diff filter. But it's
the only way because of the diff_status_letters[] mapping. Add a new
API to set diff filter and use it in git-am. diff_opt_parse()'s only
remaining call site in revision.c will be gone soon and having it here
just because of git-am does not make sense.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/diff.h b/diff.h
index 03c6afda22..f88482705c 100644
--- a/diff.h
+++ b/diff.h
@@ -233,6 +233,8 @@ struct diff_options {
 	struct option *parseopts;
 };
 
+unsigned diff_filter_bit(char status);
+
 void diff_emit_submodule_del(struct diff_options *o, const char *line);
 void diff_emit_submodule_add(struct diff_options *o, const char *line);
 void diff_emit_submodule_untracked(struct diff_options *o, const char *path);