diff: add -I<regex> that ignores matching changes

Add a new diff option that enables ignoring changes whose all lines
(changed, removed, and added) match a given regular expression.  This is
similar to the -I/--ignore-matching-lines option in standalone diff
utilities and can be used e.g. to ignore changes which only affect code
comments or to look for unrelated changes in commits containing a large
number of automatically applied modifications (e.g. a tree-wide string
replacement).  The difference between -G/-S and the new -I option is
that the latter filters output on a per-change basis.

Use the 'ignore' field of xdchange_t for marking a change as ignored or
not.  Since the same field is used by --ignore-blank-lines, identical
hunk emitting rules apply for --ignore-blank-lines and -I.  These two
options can also be used together in the same git invocation (they are
complementary to each other).

Rename xdl_mark_ignorable() to xdl_mark_ignorable_lines(), to indicate
that it is logically a "sibling" of xdl_mark_ignorable_regex() rather
than its "parent".

Signed-off-by: Michał Kępień <michal@isc.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/diff.h b/diff.h
index 9443dc1b00..976f83e031 100644
--- a/diff.h
+++ b/diff.h
@@ -234,6 +234,10 @@ struct diff_options {
 	 */
 	const char *pickaxe;
 
+	/* -I<regex> */
+	regex_t **ignore_regex;
+	size_t ignore_regex_nr, ignore_regex_alloc;
+
 	const char *single_follow;
 	const char *a_prefix, *b_prefix;
 	const char *line_prefix;