sparse-checkout: reuse --stdin buffer when reading patterns

When we read patterns from --stdin, we loop on strbuf_getline(), and
detach each line we read to pass into add_pattern(). This used to be
necessary because add_pattern() required that the pattern strings remain
valid while the pattern_list was in use. But it also created a leak,
since we didn't record the detached buffers anywhere else.

Now that add_pattern() has been modified to make its own copy of the
strings, we can stop detaching and fix the leak. This fixes 4 leaks
detected in t1091.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/sparse-checkout.c

@@ -585,11 +585,10 @@ static void add_patterns_from_input(struct pattern_list *pl,
 		if (file) {
 			struct strbuf line = STRBUF_INIT;
 
-			while (!strbuf_getline(&line, file)) {
-				size_t len;
-				char *buf = strbuf_detach(&line, &len);
-				add_pattern(buf, empty_base, 0, pl, 0);
-			}
+			while (!strbuf_getline(&line, file))
+				add_pattern(line.buf, empty_base, 0, pl, 0);
+
+			strbuf_release(&line);
 		} else {
 			for (i = 0; i < argc; i++)
 				add_pattern(argv[i], empty_base, 0, pl, 0);