xdiff: -W: don't include common trailing empty lines in context

Empty lines between functions are shown by diff -W, as it considers them
to be part of the function preceding them.  They are not interesting in
most languages.  The previous patch stopped showing them in the special
case of a function added at the end of a file.

Stop extending context to those empty lines by skipping back over them
from the start of the next function.

Signed-off-by: Rene Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t4051-diff-function-context.sh

@@ -85,7 +85,7 @@ test_expect_success ' context does not include preceding empty lines' '
 	test "$(first_context_line <changed_hello.diff)" != " "
 '
 
-test_expect_failure ' context does not include trailing empty lines' '
+test_expect_success ' context does not include trailing empty lines' '
 	test "$(last_context_line <changed_hello.diff)" != " "
 '
 
@@ -103,7 +103,7 @@ test_expect_success ' context does not include other functions' '
 	test $(grep -c "^[ +-].*Begin" changed_includes.diff) -le 1
 '
 
-test_expect_failure ' context does not include trailing empty lines' '
+test_expect_success ' context does not include trailing empty lines' '
 	test "$(last_context_line <changed_includes.diff)" != " "
 '
 

xdiff/xemit.c

@@ -231,6 +231,8 @@ int xdl_emit_diff(xdfenv_t *xe, xdchange_t *xscr, xdemitcb_t *ecb,
 			long fe1 = get_func_line(xe, xecfg, NULL,
 						 xche->i1 + xche->chg1,
 						 xe->xdf1.nrec);
+			while (fe1 > 0 && is_empty_rec(&xe->xdf1, fe1 - 1))
+				fe1--;
 			if (fe1 < 0)
 				fe1 = xe->xdf1.nrec;
 			if (fe1 > e1) {