diff: futureproof "stop feeding the backend early" logic

Refactor the "do not stop feeding the backend early" logic into a small
helper function and use it in both run_diff_files() and diff_tree() that
has the stop-early optimization. We may later add other types of diffcore
transformation that require to look at the whole result like diff-filter
does, and having the logic in a single place is essential for longer term
maintainability.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/diff.c b/diff.c
index 91d6ea21a9..ae6853fcf1 100644
--- a/diff.c
+++ b/diff.c
@@ -3513,6 +3513,13 @@ int diff_result_code(struct diff_options *opt, int status)
 	return result;
 }
 
+int diff_can_quit_early(struct diff_options *opt)
+{
+	return (DIFF_OPT_TST(opt, QUICK) &&
+		!opt->filter &&
+		DIFF_OPT_TST(opt, HAS_CHANGES));
+}
+
 void diff_addremove(struct diff_options *options,
 		    int addremove, unsigned mode,
 		    const unsigned char *sha1,