pack-objects: lazily set up "struct rev_info", don't leak

In the preceding [1] (pack-objects: move revs out of
get_object_list(), 2022-03-22) the "repo_init_revisions()" was moved
to cmd_pack_objects() so that it unconditionally took place for all
invocations of "git pack-objects".

We'd thus start leaking memory, which is easily reproduced in
e.g. git.git by feeding e83c516 (Initial revision of "git", the
information manager from hell, 2005-04-07) to "git pack-objects";

    $ echo e83c516 | ./git pack-objects initial
    [...]
	==19130==ERROR: LeakSanitizer: detected memory leaks

	Direct leak of 7120 byte(s) in 1 object(s) allocated from:
	    #0 0x455308 in __interceptor_malloc (/home/avar/g/git/git+0x455308)
	    #1 0x75b399 in do_xmalloc /home/avar/g/git/wrapper.c:41:8
	    #2 0x75b356 in xmalloc /home/avar/g/git/wrapper.c:62:9
	    #3 0x5d7609 in prep_parse_options /home/avar/g/git/diff.c:5647:2
	    #4 0x5d415a in repo_diff_setup /home/avar/g/git/diff.c:4621:2
	    #5 0x6dffbb in repo_init_revisions /home/avar/g/git/revision.c:1853:2
	    #6 0x4f599d in cmd_pack_objects /home/avar/g/git/builtin/pack-objects.c:3980:2
	    #7 0x4592ca in run_builtin /home/avar/g/git/git.c:465:11
	    #8 0x457d81 in handle_builtin /home/avar/g/git/git.c:718:3
	    #9 0x458ca5 in run_argv /home/avar/g/git/git.c:785:4
	    #10 0x457b40 in cmd_main /home/avar/g/git/git.c:916:19
	    #11 0x562259 in main /home/avar/g/git/common-main.c:56:11
	    #12 0x7fce792ac7ec in __libc_start_main csu/../csu/libc-start.c:332:16
	    #13 0x4300f9 in _start (/home/avar/g/git/git+0x4300f9)

	SUMMARY: LeakSanitizer: 7120 byte(s) leaked in 1 allocation(s).
	Aborted

Narrowly fixing that commit would have been easy, just add call
repo_init_revisions() right before get_object_list(), which is
effectively what was done before that commit.

But an unstated constraint when setting it up early is that it was
needed for the subsequent [2] (pack-objects: parse --filter directly
into revs.filter, 2022-03-22), i.e. we might have a --filter
command-line option, and need to either have the "struct rev_info"
setup when we encounter that option, or later.

Let's just change the control flow so that we'll instead set up the
"struct rev_info" only when we need it. Doing so leads to a bit more
verbosity, but it's a lot clearer what we're doing and why.

An earlier version of this commit[3] went behind
opt_parse_list_objects_filter()'s back by faking up a "struct option"
before calling it. Let's avoid that and instead create a blessed API
for this pattern.

We could furthermore combine the two get_object_list() invocations
here by having repo_init_revisions() invoked on &pfd.revs, but I think
clearly separating the two makes the flow clearer. Likewise
redundantly but explicitly (i.e. redundant v.s. a "{ 0 }") "0" to
"have_revs" early in cmd_pack_objects().

While we're at it add parentheses around the arguments to the OPT_*
macros in in list-objects-filter-options.h, as we need to change those
lines anyway. It doesn't matter in this case, but is good general
practice.

1. https://lore.kernel.org/git/619b757d98465dbc4995bdc11a5282fbfcbd3daa.1647970119.git.gitgitgadget@gmail.com
2. https://lore.kernel.org/git/97de926904988b89b5663bd4c59c011a1723a8f5.1647970119.git.gitgitgadget@gmail.com
3. https://lore.kernel.org/git/[email protected]/

Signed-off-by: Ævar Arnfjörð Bjarmason <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: avar

builtin/pack-objects.c

@@ -3857,6 +3857,21 @@ static int option_parse_unpack_unreachable(const struct option *opt,
 	return 0;
 }
 
+struct po_filter_data {
+	unsigned have_revs:1;
+	struct rev_info revs;
+};
+
+static struct list_objects_filter_options *po_filter_revs_init(void *value)
+{
+	struct po_filter_data *data = value;
+
+	repo_init_revisions(the_repository, &data->revs, NULL);
+	data->have_revs = 1;
+
+	return &data->revs.filter;
+}
+
 int cmd_pack_objects(int argc, const char **argv, const char *prefix)
 {
 	int use_internal_rev_list = 0;
@@ -3867,7 +3882,7 @@ int cmd_pack_objects(int argc, const char **argv, const char *prefix)
 	int rev_list_index = 0;
 	int stdin_packs = 0;
 	struct string_list keep_pack_list = STRING_LIST_INIT_NODUP;
-	struct rev_info revs;
+	struct po_filter_data pfd = { .have_revs = 0 };
 
 	struct option pack_objects_options[] = {
 		OPT_SET_INT('q', "quiet", &progress,
@@ -3954,7 +3969,7 @@ int cmd_pack_objects(int argc, const char **argv, const char *prefix)
 			      &write_bitmap_index,
 			      N_("write a bitmap index if possible"),
 			      WRITE_BITMAP_QUIET, PARSE_OPT_HIDDEN),
-		OPT_PARSE_LIST_OBJECTS_FILTER(&revs.filter),
+		OPT_PARSE_LIST_OBJECTS_FILTER_INIT(&pfd, po_filter_revs_init),
 		OPT_CALLBACK_F(0, "missing", NULL, N_("action"),
 		  N_("handling for missing objects"), PARSE_OPT_NONEG,
 		  option_parse_missing_action),
@@ -3973,8 +3988,6 @@ int cmd_pack_objects(int argc, const char **argv, const char *prefix)
 
 	read_replace_refs = 0;
 
-	repo_init_revisions(the_repository, &revs, NULL);
-
 	sparse = git_env_bool("GIT_TEST_PACK_SPARSE", -1);
 	if (the_repository->gitdir) {
 		prepare_repo_settings(the_repository);
@@ -4076,7 +4089,7 @@ int cmd_pack_objects(int argc, const char **argv, const char *prefix)
 	if (!rev_list_all || !rev_list_reflog || !rev_list_index)
 		unpack_unreachable_expiration = 0;
 
-	if (revs.filter.choice) {
+	if (pfd.have_revs && pfd.revs.filter.choice) {
 		if (!pack_to_stdout)
 			die(_("cannot use --filter without --stdout"));
 		if (stdin_packs)
@@ -4152,7 +4165,12 @@ int cmd_pack_objects(int argc, const char **argv, const char *prefix)
 			add_unreachable_loose_objects();
 	} else if (!use_internal_rev_list) {
 		read_object_list_from_stdin();
+	} else if (pfd.have_revs) {
+		get_object_list(&pfd.revs, rp.nr, rp.v);
 	} else {
+		struct rev_info revs;
+
+		repo_init_revisions(the_repository, &revs, NULL);
 		get_object_list(&revs, rp.nr, rp.v);
 	}
 	cleanup_preferred_base();

list-objects-filter-options.c

@@ -285,6 +285,10 @@ int opt_parse_list_objects_filter(const struct option *opt,
 				  const char *arg, int unset)
 {
 	struct list_objects_filter_options *filter_options = opt->value;
+	opt_lof_init init = (opt_lof_init)opt->defval;
+
+	if (init)
+		filter_options = init(opt->value);
 
 	if (unset || !arg)
 		list_objects_filter_set_no_filter(filter_options);

list-objects-filter-options.h

@@ -104,13 +104,31 @@ void parse_list_objects_filter(
 	struct list_objects_filter_options *filter_options,
 	const char *arg);
 
+/**
+ * The opt->value to opt_parse_list_objects_filter() is either a
+ * "struct list_objects_filter_option *" when using
+ * OPT_PARSE_LIST_OBJECTS_FILTER().
+ *
+ * Or, if using no "struct option" field is used by the callback,
+ * except the "defval" which is expected to be an "opt_lof_init"
+ * function, which is called with the "opt->value" and must return a
+ * pointer to the ""struct list_objects_filter_option *" to be used.
+ *
+ * The OPT_PARSE_LIST_OBJECTS_FILTER_INIT() can be used e.g. the
+ * "struct list_objects_filter_option" is embedded in a "struct
+ * rev_info", which the "defval" could be tasked with lazily
+ * initializing. See cmd_pack_objects() for an example.
+ */
 int opt_parse_list_objects_filter(const struct option *opt,
 				  const char *arg, int unset);
+typedef struct list_objects_filter_options *(*opt_lof_init)(void *);
+#define OPT_PARSE_LIST_OBJECTS_FILTER_INIT(fo, init) \
+	{ OPTION_CALLBACK, 0, "filter", (fo), N_("args"), \
+	  N_("object filtering"), 0, opt_parse_list_objects_filter, \
+	  (intptr_t)(init) }
 
 #define OPT_PARSE_LIST_OBJECTS_FILTER(fo) \
-	OPT_CALLBACK(0, "filter", fo, N_("args"), \
-	  N_("object filtering"), \
-	  opt_parse_list_objects_filter)
+	OPT_PARSE_LIST_OBJECTS_FILTER_INIT((fo), NULL)
 
 /*
  * Translates abbreviated numbers in the filter's filter_spec into their