index-pack: use xopen in init_thread

Support an arbitrary file descriptor expression in the semantic patch
for replacing open+die_errno with xopen, not just an identifier, and
apply it.  This makes the error message at the single affected place
more consistent and reduces code duplication.

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

builtin/index-pack.c

@@ -187,9 +187,7 @@ static void init_thread(void)
 	pthread_key_create(&key, NULL);
 	CALLOC_ARRAY(thread_data, nr_threads);
 	for (i = 0; i < nr_threads; i++) {
-		thread_data[i].pack_fd = open(curr_pack, O_RDONLY);
-		if (thread_data[i].pack_fd == -1)
-			die_errno(_("unable to open %s"), curr_pack);
+		thread_data[i].pack_fd = xopen(curr_pack, O_RDONLY);
 	}
 
 	threads_active = 1;

contrib/coccinelle/xopen.cocci

@@ -2,15 +2,18 @@
 identifier fd;
 identifier die_fn =~ "^(die|die_errno)$";
 @@
-(
-  fd =
-- open
-+ xopen
-  (...);
-|
   int fd =
 - open
 + xopen
   (...);
-)
+- if ( \( fd < 0 \| fd == -1 \) ) { die_fn(...); }
+
+@@
+expression fd;
+identifier die_fn =~ "^(die|die_errno)$";
+@@
+  fd =
+- open
++ xopen
+  (...);
 - if ( \( fd < 0 \| fd == -1 \) ) { die_fn(...); }