Re: [RFH] xdiff shows trivially redundant diff.

Davide Libenzi [off-list ref] writes:

No problem. That's only an eye-issue though, since the diff is still a
valid diff according to its definition where D=A-B => B+D==A && A-D==B
From the day I released 0.18, xregression is continuosly running w/out
any issue. I'll check it out though ...

There is another to report, when ctxlen == 0.

Between the attached files "diff -u0 8f352aa dd40a03", the 
header for a hunk with only inserted lines misidentify the
original location.

For example, the first hunk says:

	@@ -0,0 +6 @@
        +#include "diff.h"

Which is inconsistent with what GNU diff says:

	@@ -5,0 +6 @@
        +#include "diff.h"

I've tried this patch but it is not right; the diff between the
attached two files show a 47-line hunk that inserts at line 400,
then the next 6-line hunk inserts at line 401 which is obviously
bogus.

diff --git a/xdiff/xutils.c b/xdiff/xutils.c
index afaada1..3e7f999 100644
--- a/xdiff/xutils.c
+++ b/xdiff/xutils.c

@@ -244,7 +244,7 @@ int xdl_emit_hunk_hdr(long s1, long c1, 
 	memcpy(buf, "@@ -", 4);
 	nb += 4;
 
-	nb += xdl_num_out(buf + nb, c1 ? s1: 0);
+	nb += xdl_num_out(buf + nb, c1 ? s1 : (s1-1));
 
 	if (c1 != 1) {
 		memcpy(buf + nb, ",", 1);