diff: deprecate -q option to diff-files

This reimplements the ancient "-q" option to "git diff-files" that
was inherited from "show-diff -q" in terms of "--diff-filter=d".  We
will be deprecating the "-q" option, so let's issue a warning when
we do so.

Incidentally this also tentatively fixes "git diff --no-index" to
honor "-q" and hide deletions; the use will get the same warning.

We should remove the support for "-q" in a future version but it is
not that urgent.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/diff.c b/diff.c
index 2d0b5e3..78819ba 100644
--- a/diff.c
+++ b/diff.c
@@ -3570,6 +3570,14 @@
 	return 0;
 }
 
+/* Used only by "diff-files" and "diff --no-index" */
+void handle_deprecated_show_diff_q(struct diff_options *opt)
+{
+	warning("'diff -q' and 'diff-files -q' are deprecated.");
+	warning("Use 'diff --diff-filter=d' instead to ignore deleted filepairs.");
+	parse_diff_filter_opt("d", opt);
+}
+
 int diff_opt_parse(struct diff_options *options, const char **av, int ac)
 {
 	const char *arg = av[0];