patch: fix matching failure

Fix matching failure when plist is advanced while checking for buffered
lines - the lines in the hunk that are about to be added should be
skipped when checking for matching context.

Also add a valid test case that fails with current busybox and is fixed
by the change.

Signed-off-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

editors/patch.c

@@ -290,6 +290,17 @@ static int apply_one_hunk(void)
 		// out of buffer.
 
 		for (;;) {
+			while (plist && *plist->data == "+-"[reverse]) {
+				if (!strcmp(check->data, plist->data+1) &&
+				    !backwarn) {
+					backwarn = TT.linenum;
+					if (option_mask32 & FLAG_IGNORE) {
+						dummy_revert = 1;
+						reverse ^= 1;
+					}
+				}
+				plist = plist->next;
+			}
 			if (!plist || strcmp(check->data, plist->data+1)) {
 				// Match failed.  Write out first line of buffered data and
 				// recheck remaining buffered data for a new match.

testsuite/patch.tests

@@ -242,6 +242,51 @@ patch: can't open 'dir2///file': No such file or directory
  zxc
 "
 
+testing "patch internal buffering bug?" \
+	'patch -p1 2>&1; echo $?; cat input' \
+"\
+patching file input
+0
+foo
+
+
+
+
+
+
+1
+2
+3
+
+bar
+" \
+"\
+foo
+
+
+
+
+
+
+
+bar
+" \
+"\
+--- a/input.orig
++++ b/input
+@@ -5,5 +5,8 @@ foo
+ 
+ 
+ 
++1
++2
++3
+ 
+ bar
+-- 
+2.9.2
+" \
+
 rm input.orig 2>/dev/null
 
 exit $FAILCOUNT