built-in diff: minimum tweaks

This fixes up a couple of minor issues with the real built-in
diff to be more usable:

 - Omit ---/+++ header unless we emit diff output;

 - Detect and punt binary diff like GNU does;

 - Honor GIT_DIFF_OPTS minimally (only -u<number> and
   --unified=<number> are currently supported);

 - Omit line count of 1 from "@@ -l,k +m,n @@" hunk header
   (i.e. when k == 1 or n == 1)

 - Adjust testsuite for the lack of -p support.

Signed-off-by: Junio C Hamano <junkio@cox.net>

1 files changed, 10 insertions, 6 deletions

diff --git a/xdiff/xutils.c b/xdiff/xutils.c
index b68afa25c..8221806f7 100644
--- a/xdiff/xutils.c
+++ b/xdiff/xutils.c
@@ -245,20 +245,24 @@ int xdl_emit_hunk_hdr(long s1, long c1, long s2, long c2, xdemitcb_t *ecb) {
 
 	nb += xdl_num_out(buf + nb, c1 ? s1: 0);
 
-	memcpy(buf + nb, ",", 1);
-	nb += 1;
+	if (c1 != 1) {
+		memcpy(buf + nb, ",", 1);
+		nb += 1;
 
-	nb += xdl_num_out(buf + nb, c1);
+		nb += xdl_num_out(buf + nb, c1);
+	}
 
 	memcpy(buf + nb, " +", 2);
 	nb += 2;
 
 	nb += xdl_num_out(buf + nb, c2 ? s2: 0);
 
-	memcpy(buf + nb, ",", 1);
-	nb += 1;
+	if (c2 != 1) {
+		memcpy(buf + nb, ",", 1);
+		nb += 1;
 
-	nb += xdl_num_out(buf + nb, c2);
+		nb += xdl_num_out(buf + nb, c2);
+	}
 
 	memcpy(buf + nb, " @@\n", 4);
 	nb += 4;