list-objects-filter-options: work around reported leak on error

This one is a little bit more curious. In t6112, we have a test that
exercises the `git rev-list --filter` option with invalid filters. We
execute git-rev-list(1) via `test_must_fail`, which means that we check
for leaks even though Git exits with an error code. This causes the
following leak:

    Direct leak of 27 byte(s) in 1 object(s) allocated from:
        #0 0x5555555e6946 in realloc.part.0 lsan_interceptors.cpp.o
        #1 0x5555558fb4b6 in xrealloc wrapper.c:137:8
        #2 0x5555558b6e06 in strbuf_grow strbuf.c:112:2
        #3 0x5555558b7550 in strbuf_add strbuf.c:311:2
        #4 0x5555557c1a88 in strbuf_addstr strbuf.h:310:2
        #5 0x5555557c1d4c in parse_list_objects_filter list-objects-filter-options.c:261:3
        #6 0x555555885ead in handle_revision_pseudo_opt revision.c:2899:3
        #7 0x555555884e20 in setup_revisions revision.c:3014:11
        #8 0x5555556c4b42 in cmd_rev_list builtin/rev-list.c:588:9
        #9 0x5555555ec5e3 in run_builtin git.c:483:11
        #10 0x5555555eb1e4 in handle_builtin git.c:749:13
        #11 0x5555555ec001 in run_argv git.c:819:4
        #12 0x5555555eaf94 in cmd_main git.c:954:19
        #13 0x5555556fd569 in main common-main.c:64:11
        #14 0x7ffff7ca714d in __libc_start_call_main (.../lib/libc.so.6+0x2a14d)
        #15 0x7ffff7ca7208 in __libc_start_main@GLIBC_2.2.5 (.../libc.so.6+0x2a208)
        #16 0x5555555ad064 in _start (git+0x59064)

This leak is valid, as we call `die()` and do not clean up the memory at
all. But what's curious is that this is the only leak reported, because
we don't clean up any other allocated memory, either, and I have no idea
why the leak sanitizer treats this buffer specially.

In any case, we can work around the leak by shuffling things around a
bit. Instead of calling `gently_parse_list_objects_filter()` and dying
after we have modified the filter spec, we simply do so beforehand. Like
this we don't allocate the buffer in the error case, which makes the
reported leak go away.

It's not pretty, but it manages to make t6112 leak free.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Taylor Blau <me@ttaylorr.com>

Author: pks-t

list-objects-filter-options.c

@@ -252,16 +252,14 @@ void parse_list_objects_filter(
 	const char *arg)
 {
 	struct strbuf errbuf = STRBUF_INIT;
-	int parse_error;
 
 	if (!filter_options->filter_spec.buf)
 		BUG("filter_options not properly initialized");
 
 	if (!filter_options->choice) {
+		if (gently_parse_list_objects_filter(filter_options, arg, &errbuf))
+			die("%s", errbuf.buf);
 		strbuf_addstr(&filter_options->filter_spec, arg);
-
-		parse_error = gently_parse_list_objects_filter(
-			filter_options, arg, &errbuf);
 	} else {
 		struct list_objects_filter_options *sub;
 
@@ -271,18 +269,17 @@ void parse_list_objects_filter(
 		 */
 		transform_to_combine_type(filter_options);
 
-		strbuf_addch(&filter_options->filter_spec, '+');
-		filter_spec_append_urlencode(filter_options, arg);
 		ALLOC_GROW_BY(filter_options->sub, filter_options->sub_nr, 1,
 			      filter_options->sub_alloc);
 		sub = &filter_options->sub[filter_options->sub_nr - 1];
 
 		list_objects_filter_init(sub);
-		parse_error = gently_parse_list_objects_filter(sub, arg,
-							       &errbuf);
+		if (gently_parse_list_objects_filter(sub, arg, &errbuf))
+			die("%s", errbuf.buf);
+
+		strbuf_addch(&filter_options->filter_spec, '+');
+		filter_spec_append_urlencode(filter_options, arg);
 	}
-	if (parse_error)
-		die("%s", errbuf.buf);
 }
 
 int opt_parse_list_objects_filter(const struct option *opt,

t/t6112-rev-list-filters-objects.sh

@@ -5,6 +5,7 @@ test_description='git rev-list using object filtering'
 GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=main
 export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
 
+TEST_PASSES_SANITIZE_LEAK=true
 . ./test-lib.sh
 
 # Test the blob:none filter.