builtin/repack: fix leaks when computing packs to repack

When writing an MIDX in git-repack(1) we first collect all the pack
names that we want to add to it in a string list. This list is marked as
`NODUP`, which indicates that it will neither duplicate nor own strings
added to it. In `write_midx_included_packs()` we then `insert()` strings
via `xstrdup()` or `strbuf_detach()`, but the resulting strings will not
be owned by anything and thus leak.

Fix this issue by marking the list as `DUP` and using a local buffer to
compute the pack names.

This leak is hit in t5319, but plugging it is not sufficient to make the
whole test suite pass.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: pks-t

builtin/repack.c

@@ -732,14 +732,23 @@ static void midx_included_packs(struct string_list *include,
 				struct pack_geometry *geometry)
 {
 	struct string_list_item *item;
+	struct strbuf buf = STRBUF_INIT;
+
+	for_each_string_list_item(item, &existing->kept_packs) {
+		strbuf_reset(&buf);
+		strbuf_addf(&buf, "%s.idx", item->string);
+		string_list_insert(include, buf.buf);
+	}
+
+	for_each_string_list_item(item, names) {
+		strbuf_reset(&buf);
+		strbuf_addf(&buf, "pack-%s.idx", item->string);
+		string_list_insert(include, buf.buf);
+	}
 
-	for_each_string_list_item(item, &existing->kept_packs)
-		string_list_insert(include, xstrfmt("%s.idx", item->string));
-	for_each_string_list_item(item, names)
-		string_list_insert(include, xstrfmt("pack-%s.idx", item->string));
 	if (geometry->split_factor) {
-		struct strbuf buf = STRBUF_INIT;
 		uint32_t i;
+
 		for (i = geometry->split; i < geometry->pack_nr; i++) {
 			struct packed_git *p = geometry->pack[i];
 
@@ -754,17 +763,21 @@ static void midx_included_packs(struct string_list *include,
 			if (!p->pack_local)
 				continue;
 
+			strbuf_reset(&buf);
 			strbuf_addstr(&buf, pack_basename(p));
 			strbuf_strip_suffix(&buf, ".pack");
 			strbuf_addstr(&buf, ".idx");
 
-			string_list_insert(include, strbuf_detach(&buf, NULL));
+			string_list_insert(include, buf.buf);
 		}
 	} else {
 		for_each_string_list_item(item, &existing->non_kept_packs) {
 			if (pack_is_marked_for_deletion(item))
 				continue;
-			string_list_insert(include, xstrfmt("%s.idx", item->string));
+
+			strbuf_reset(&buf);
+			strbuf_addf(&buf, "%s.idx", item->string);
+			string_list_insert(include, buf.buf);
 		}
 	}
 
@@ -784,8 +797,13 @@ static void midx_included_packs(struct string_list *include,
 		 */
 		if (pack_is_marked_for_deletion(item))
 			continue;
-		string_list_insert(include, xstrfmt("%s.idx", item->string));
+
+		strbuf_reset(&buf);
+		strbuf_addf(&buf, "%s.idx", item->string);
+		string_list_insert(include, buf.buf);
 	}
+
+	strbuf_release(&buf);
 }
 
 static int write_midx_included_packs(struct string_list *include,
@@ -1476,7 +1494,7 @@ int cmd_repack(int argc, const char **argv, const char *prefix)
 		mark_packs_for_deletion(&existing, &names);
 
 	if (write_midx) {
-		struct string_list include = STRING_LIST_INIT_NODUP;
+		struct string_list include = STRING_LIST_INIT_DUP;
 		midx_included_packs(&include, &existing, &names, &geometry);
 
 		ret = write_midx_included_packs(&include, &geometry, &names,