Subject: [PATCH 3/5] diff: ignore empty lines before added functions with -W

From: René Scharfe <[email-masked]>
Date: Sat, 21 May 2016 20:46:13 +0200

If a new function and a preceding empty line is appended, diff -W shows
the previous function in full in order to provide context for that empty
line.  In most languages empty lines between sections are not 
interesting in and off themselves and showing a whole extra function for
them is not what we want.

Skip empty lines when checking of the appended chunk starts with a
function line, thereby avoiding to extend the context just for them.

Signed-off-by: Rene Scharfe <[email-masked]>
---
 xdiff/xemit.c | 22 ++++++++++++++++++++--
 1 file changed, 20 insertions(+), 2 deletions(-)

diff --git a/xdiff/xemit.c b/xdiff/xemit.c
index 969100d..087956a 100644
--- a/xdiff/xemit.c
+++ b/xdiff/xemit.c
@@ -155,6 +155,18 @@ static long get_func_line(xdfenv_t *xe, xdemitconf_t const *xecfg,
 	return -1;
 }
 
+static int is_empty_rec(xdfile_t *xdf, xdemitconf_t const *xecfg, long ri)
+{
+	const char *rec;
+	long len = xdl_get_rec(xdf, ri, &rec);
+
+	while (len > 0 && isspace(*rec)) {
+		rec++;
+		len--;
+	}
+	return !len;
+}
+
 int xdl_emit_diff(xdfenv_t *xe, xdchange_t *xscr, xdemitcb_t *ecb,
 		  xdemitconf_t const *xecfg) {
 	long s1, s2, e1, e2, lctx;
@@ -176,12 +188,18 @@ int xdl_emit_diff(xdfenv_t *xe, xdchange_t *xscr, xdemitcb_t *ecb,
 			/* Appended chunk? */
 			if (i1 >= xe->xdf1.nrec) {
 				char dummy[1];
+				long i2 = xch->i2;
 
 				/*
 				 * We don't need additional context if
-				 * a whole function was added.
+				 * a whole function was added, possibly
+				 * starting with empty lines.
 				 */
-				if (match_func_rec(&xe->xdf2, xecfg, xch->i2,
+				while (i2 < xe->xdf2.nrec &&
+				       is_empty_rec(&xe->xdf2, xecfg, i2))
+					i2++;
+				if (i2 < xe->xdf2.nrec &&
+				    match_func_rec(&xe->xdf2, xecfg, i2,
 						   dummy, sizeof(dummy)) >= 0)
 					goto post_context_calculation;
 
-- 
2.8.3