Fix pack.packSizeLimit and --max-pack-size handling

If the limit was sufficiently low, having a single object written
could bust the limit (by design), but caused the remaining allowed
size to go negative for subsequent objects, which for an unsigned
variable is a rather huge limit.

Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-pack-objects.c

@@ -245,8 +245,16 @@ static unsigned long write_object(struct sha1file *f,
 	type = entry->type;
 
 	/* write limit if limited packsize and not first object */
-	limit = pack_size_limit && nr_written ?
-			pack_size_limit - write_offset : 0;
+	if (!pack_size_limit || !nr_written)
+		limit = 0;
+	else if (pack_size_limit <= write_offset)
+		/*
+		 * the earlier object did not fit the limit; avoid
+		 * mistaking this with unlimited (i.e. limit = 0).
+		 */
+		limit = 1;
+	else
+		limit = pack_size_limit - write_offset;
 
 	if (!entry->delta)
 		usable_delta = 0;	/* no delta */

t/t5300-pack-object.sh

@@ -375,4 +375,10 @@ test_expect_success 'index-pack with --strict' '
 	)
 '
 
+test_expect_success 'tolerate absurdly small packsizelimit' '
+	git config pack.packSizeLimit 2 &&
+	packname_9=$(git pack-objects test-9 <obj-list) &&
+	test $(wc -l <obj-list) = $(ls test-9-*.pack | wc -l)
+'
+
 test_done