revisions API users: use release_revisions() needing REV_INFO_INIT

Use release_revisions() to various users of "struct rev_list" which
need to have their "struct rev_info" zero-initialized before we can
start using it.

For the bundle.c code see the early exit case added in
3bbbe467f2 (bundle verify: error out if called without an object
database, 2019-05-27).

For the relevant bisect.c code see 45b6370812 (bisect: libify
`check_good_are_ancestors_of_bad` and its dependents, 2020-02-17).

For the submodule.c code see the "goto" on "(!left || !right || !sub)"
added in 8e6df65015 (submodule: refactor show_submodule_summary with
helper function, 2016-08-31).

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

revision.h

@@ -329,6 +329,25 @@ struct rev_info {
 	struct tmp_objdir *remerge_objdir;
 };
 
+/**
+ * Initialize the "struct rev_info" structure with a macro.
+ *
+ * This will not fully initialize a "struct rev_info", the
+ * repo_init_revisions() function needs to be called before
+ * setup_revisions() and any revision walking takes place.
+ *
+ * Use REV_INFO_INIT to make the "struct rev_info" safe for passing to
+ * release_revisions() when it's inconvenient (e.g. due to a "goto
+ * cleanup" pattern) to arrange for repo_init_revisions() to be called
+ * before release_revisions() is called.
+ *
+ * Initializing with this REV_INFO_INIT is redundant to invoking
+ * repo_init_revisions(). If repo_init_revisions() is guaranteed to be
+ * called before release_revisions() the "struct rev_info" can be left
+ * uninitialized.
+ */
+#define REV_INFO_INIT { 0 }
+
 /**
  * Initialize a rev_info structure with default values. The third parameter may
  * be NULL or can be prefix path, and then the `.prefix` variable will be set
@@ -363,7 +382,7 @@ int setup_revisions(int argc, const char **argv, struct rev_info *revs,
 
 /**
  * Free data allocated in a "struct rev_info" after it's been
- * initialized with repo_init_revisions().
+ * initialized with repo_init_revisions() or REV_INFO_INIT.
  */
 void release_revisions(struct rev_info *revs);