builtin/notes: fix leaking struct notes_tree when merging notes

We allocate a `struct notes_tree` in `merge_commit()` which we then
initialize via `init_notes()`. It's not really necessary to allocate the
structure though given that we never pass ownership to the caller.
Furthermore, the allocation leads to a memory leak because despite its
name, `free_notes()` doesn't free the `notes_tree` but only clears it.

Fix this issue by converting the code to use an on-stack variable.

Signed-off-by: Patrick Steinhardt <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: pks-t

builtin/notes.c

@@ -807,7 +807,7 @@ static int merge_commit(struct notes_merge_options *o)
 {
 	struct strbuf msg = STRBUF_INIT;
 	struct object_id oid, parent_oid;
-	struct notes_tree *t;
+	struct notes_tree t = {0};
 	struct commit *partial;
 	struct pretty_print_context pretty_ctx;
 	void *local_ref_to_free;
@@ -830,16 +830,15 @@ static int merge_commit(struct notes_merge_options *o)
 	else
 		oidclr(&parent_oid, the_repository->hash_algo);
 
-	CALLOC_ARRAY(t, 1);
-	init_notes(t, "NOTES_MERGE_PARTIAL", combine_notes_overwrite, 0);
+	init_notes(&t, "NOTES_MERGE_PARTIAL", combine_notes_overwrite, 0);
 
 	o->local_ref = local_ref_to_free =
 		refs_resolve_refdup(get_main_ref_store(the_repository),
 				    "NOTES_MERGE_REF", 0, &oid, NULL);
 	if (!o->local_ref)
 		die(_("failed to resolve NOTES_MERGE_REF"));
 
-	if (notes_merge_commit(o, t, partial, &oid))
+	if (notes_merge_commit(o, &t, partial, &oid))
 		die(_("failed to finalize notes merge"));
 
 	/* Reuse existing commit message in reflog message */
@@ -853,7 +852,7 @@ static int merge_commit(struct notes_merge_options *o)
 			is_null_oid(&parent_oid) ? NULL : &parent_oid,
 			0, UPDATE_REFS_DIE_ON_ERR);
 
-	free_notes(t);
+	free_notes(&t);
 	strbuf_release(&msg);
 	ret = merge_abort(o);
 	free(local_ref_to_free);

t/t3310-notes-merge-manual-resolve.sh

@@ -5,6 +5,7 @@
 
 test_description='Test notes merging with manual conflict resolution'
 
+TEST_PASSES_SANITIZE_LEAK=true
 . ./test-lib.sh
 
 # Set up a notes merge scenario with different kinds of conflicts

t/t3311-notes-merge-fanout.sh

@@ -5,6 +5,7 @@
 
 test_description='Test notes merging at various fanout levels'
 
+TEST_PASSES_SANITIZE_LEAK=true
 . ./test-lib.sh
 
 verify_notes () {