log: fix a memory leak in "git show <revision>..."

Fix a memory leak in code added in 5d7eeee2ac6 (git-show: grok blobs,
trees and tags, too, 2006-12-14). As we iterate over a "<revision>..."
command-line and encounter ad OBJ_COMMIT we want to use our "struct
rev_info", but with a "pending" array of one element: the one commit
we're showing in the loop.

To do this 5d7eeee2ac6 saved away a pointer to rev.pending.objects and
rev.pending.nr for its iteration. We'd then clobber those (and alloc)
when we needed to show an OBJ_COMMIT.

We'd therefore leak the "rev.pending" we started out with, and only
free the new "rev.pending" in the "OBJ_COMMIT" case arm as
prepare_revision_walk() would draw it down.

Let's fix this memory leak. Now when we encounter an OBJ_COMMIT we
save away the "rev.pending" before clearing it. We then add a single
commit to it, which our indirect invocation of prepare_revision_walk()
will remove. After that we restore the "rev.pending".

Our "rev.pending" will then get free'd by the release_revisions()
added in f6bfea0ad01 (revisions API users: use release_revisions() in
builtin/log.c, 2022-04-13)

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

1 files changed, 6 insertions, 0 deletions

diff --git a/builtin/log.c b/builtin/log.c
index 88a5e98875..b4b1d97461 100644
--- a/builtin/log.c
+++ b/builtin/log.c
@@ -743,11 +743,17 @@ int cmd_show(int argc, const char **argv, const char *prefix)
 			rev.shown_one = 1;
 			break;
 		case OBJ_COMMIT:
+		{
+			struct object_array old;
+
+			memcpy(&old, &rev.pending, sizeof(old));
 			rev.pending.nr = rev.pending.alloc = 0;
 			rev.pending.objects = NULL;
 			add_object_array(o, name, &rev.pending);
 			ret = cmd_log_walk_no_free(&rev);
+			memcpy(&rev.pending, &old, sizeof(rev.pending));
 			break;
+		}
 		default:
 			ret = error(_("unknown type: %d"), o->type);
 		}